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12th International Symposium on12 International Symposium on Equatorial Aeronomy

Book of Abstracts

May 18 - 24 2008 Crete GreeceMay 18 - 24, 2008. Crete, Greece

Book of Abstracts

12th International Symposium on Equatorial Aeronomy ( ISEA –12 )

ALDEMAR KNOSSOS CONFERENCE HOTEL HERSONISSOS, CRETE, GREECE

MAY 18-24, 2008

TABLE OF CONTENTS

FOREWORD ............................................................................................................................................... 1

SPONSORS .................................................................................................................................................. 3

ISEA12 COMMITTEES ........................................................................................................................... 5

ISEA12 PROGRAM OUTLINE .............................................................................................................. 7

SESSIONS AND CONVENERS ................................................................................................................. 9

PROGRAM ............................................................................................................................................... 11

ABSTRACTS ............................................................................................................................................ 39

LIST OF PARTICIPANTS.................................................................................................................... 197

FIRST/PRESENTING AUTHOR INDEX .......................................................................................... 198

1

FOREWORD The International Symposium on Equatorial Aeronomy (ISEA) has been established over the years as an important meeting for the world’s research community interested in the physics of the low- and mid-latitude upper atmosphere and ionosphere. Since the first symposium in Peru nearly five decades ago, ISEA is held regularly every 3 to 5 years in different locations around the globe. It represents an opportunity for researchers to review and evaluate their scientific achievements over the period since the previous ISEA, share their most recent results and ideas, and discuss possibilities for new directions in research, joint experiments and observational campaigns. The 12th International Symposium on Equatorial Aeronomy (ISEA-12), held from 18 to 24, May 2008 on the island of Crete, Greece, brings together senior scientists, young post-doctoral fellows and students from many countries. The topics cover a wide range of research areas, reflecting the need to study the Earth’s ionosphere - atmosphere system in a coupled sense. ISEA-12 includes sessions on dynamics of the middle atmosphere, mesosphere and thermosphere, E and F region plasma physics and ionospheric electrodynamics, including large scale ionospheric modeling, atmosphere–ionosphere coupling processes and phenomena, magnetic storm effects and space weather, and a session on new experimental techniques and instruments. In addition, and for the first time, ISEA-12 starts with two sessions of tutorials on key topics given by leading scientists, and ends with a session of invited expert talks on future research trends and unresolved problems. The vitality of the field is reflected in the full program and strong participation in ISEA-12, which includes 260 oral and poster presentations, and will be attended by over 180 participants from 26 countries. ISEA-12 is hosted by the Department of Physics, University of Crete, and is held in the Aldemar Knossos Conference Hotel near the town of Hersonissos, in Eastern Crete. The ISEA-12 organizing committees, who have been responsible for the scientific program and the overall organization, wish to cordially thank everyone for his/her attendance and valuable support of the symposium, and for his/her contribution to its success. Our gratitude is also extended to our national and international sponsors for providing funds that assisted many participants of the meeting, mostly young scientists and PhD students. The ISEA-12 organizers are pleased to extend their warmest welcome to all attendees and wish them a scientifically fruitful symposium and an enjoyable time in Crete. With kind regards, Christos Haldoupis Chair, ISEA-12 Organizing Committee

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SPONSORS We thank the following sponsors for their financial support and contribution to the success of the 12th International Symposium on Equatorial Aeronomy

1) NSF : National Science Foundation – Division of Atmospheric Sciences

2) EOARD : European Office of Aerospace Research and Development

3) The Aerospace Corporation

4) COSPAR : Committee on Space Research

5) SCOSTEP: Scientific Committee On Solar Terrestrial Physics

6) IUGG : International Union of Geodesy and Geophysics

7) IAGA : International Union of Geomagnetism and Aeronomy

8) URSI : International Union of Radio Science

9) ICG : International Committee on Global Navigation Satellite Systems

10) Greek Ministry of National Education

11) John S. Latsis, Public Benefit Foundation

12) Physics Department, University of Crete

13) ATE : Agricultural Bank of Greece

14) OTE : Hellenic Telecommunications Organization

15) LARCO General Mining and Metallurgical Company

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ISEA-12 COMMITTEES International Organizing Committee Christos Haldoupis, Chair, Greece Jorhe Chau, Peru Erhan Kudeki, USA Jonathan Makela, USA Dora Pancheva, Bulgaria Akinori Saito, Japan ISEA-12 Science Advisory Committee Bhattacharyya, A., Indian Institute of Geomagnetism, India Chau, J. Radio Observatorio Jicamarca, Peru Farley, D. Cornell University, USA Fessen, C. Dartmouth College, USA Haldoupis, C. Univeristy of Crete, Greece Heelis, R. University of Texas at Dallas, USA Hysell, D. Cornell University, USA Inan, U. Stanford University, USA Kelley, M. Cornell University, USA Kudeki, E. University of Illinois at Urbana, USA Larsen, M. Clemson University, USA Makela, J. University of Illinois at Urbana, USA Pancheva, D. Geophysical Institute, Bulgaria Pfaff, R. NASA Goddard Space Flight Center, USA Saito, A. Kyoto University, Japan St.-Maurice, J.-P. University of Saskatchewan, Canada Swenson, G. University of Illinois at Urbana, USA Vincent, B. University of Adelaide, Australia Woodman, R. Instituto Geophysico del Peru, Peru Local Organizing Committee C. Haldoupis, Chair, University of Crete N. Kylafis, University of Crete N. Christakis, University of Crete Y. Daglis, National Observatory of Athens G. P. Mantas, University of Patras N. Flytzanis, University of Crete

ISEA-12 PROGRAM OUTLINE May Saturday May 17 – Saturday May 24

Saturday 17 Sunday 18 Monday 19 Tuesday Wednesday Thursday Friday Saturday 07:30-12:30

Registration 08:30-12:30 Registration

Full Day Excursion

08:30-09:50 Opening-Session S1

08:00-10:00 Session S3

08:00-10:00 Session S5

08:00-10:00 Session S7

08:00-10:00 Session S9

08:00-10:20 Session S9

09:50-10:15 Coffee Break





10:20-10:30 Closing Remarks

10:15-12:30 Session S1

10:30-12:30 Session S3

10:30-12:30 Session S5

10:30-12:30 Session S7

10:30-12:30 Session S9


12:30-15:00 Break

12:30-14:00 Break

12:30-14:00 Break

12:30-14:00 Break

12:30-13:50 Break

11:00 End of ISEA 12

15:00-17:15 Session S2

14:00-16:00 Session S4

14:00-15:55 Session S6

14:00-15:55 Session S8

13:50-16:00 Session S10





16:30-18:30 Session S4

16:25-18:30 Session S6

16:25-18:30 Session S8

16:30-18:30 Session S10

18:30-20:00 Registration

18:30-20:00 Welcome Party

20:00-21:00 Special Lecture

20:00-23:00 Gala Dinner

08:00-20:00 Poster P1 & P2

08:00-20:00 Poster P1 & P2

08:00-20:00 Poster P3 & P4

08:00-20:00 Poster P3 & P4

Posters: Author Attendamce 13:00-14:00 and 19:00-20:00

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SESSIONS AND CONVENERS

SESSION S1 & S2 Sunday

TUTORIALS I & II (IN MEMORIAM TOR HAGFORS)

C. Haldoupis and E. Kudeki

SESSION S3 Monday Morning

EQUATORIAL LOWER- AND MIDDLE- ATMOSPHERE STUDIES G. Swenson, T. Nakamura, and J. Röttger

SESSION S4 Monday Afternoon

EQUATORIAL AND MID-LATITUDE MLT DYNAMICS D. Pancheva, A. Smith, and J. Oberheide

POSTER P1 Monday - Tuesday

POSTERS FOR SESSIONS S3 AND S4 G. Swenson and D. Pancheva

SESSION S5 Tuesday Morning

E-REGION PLASMA PHYSICS J.-P. St-Maurice, A. K. Patra, and C. De Nardini

SESSION S6 Tuesday Afternoon

F-REGION PLASMA IRREGULARITIES: CAUSES AND EFFECTS A. Bhattacharyya, R. Woodman, and M. A. Abdu

POSTER P2 Monday - Tuesday

POSTERS FOR SESSIONS S5 AND S6 J.-P. St-Maurice and A. Bhattacharyya

EXCURSION Wednesday

SESSION S7 Thursday Morning

IONOSPHERIC ELECTRODYNAMICS: THEORY AND NUMERICAL MODELING C. Fesen, J. Huba, and T. Fuller-Rowell

SESSION S8 Thursday Afternoon

COUPLING PROCESSES AT LOW- AND MID-LATITUDES M. Larsen, K. Shiokawa, and R. Cosgrove

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POSTER P3 Thursday – Friday

POSTERS FOR SESSIONS S7 AND S8 C. Fesen and M. Larsen

SESSION S9 Friday Morning

NEW TECHNIQUES, EXPERIMENTS, CAMPAIGNS, AND RESULTS D. Hysell, J. Clemmons, and M. Mila

SESSION S10 Friday Afternoon

IONOSPHERIC STORMS AND SPACE WEATHER EFFECTS R. Pfaff, L. Paxton, and D. Pallamraju

POSTER P4 Thursday – Friday

POSTERS FOR SESSIONS S9 AND S10 D. Hysell and R. Pfaff

SESSION S11 Saturday Morning

WHERE ARE WE GOING? OUTSTANDING QUESTIONS, FUTURE TRENDS AND CHALLENGES M. C. Kelley and E. Kudeki

12th International Symposium on Equatorial Aeronomy – May 18 - 24, 2008, Crete, Greece

ISEA-12 Program

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12TH INTERNATIONAL SYMPOSIUM ON EQUATORIAL AERONOMY (ISEA-12)

PROGRAM

SATURDAY MAY 17, 2008

18:30 – 20:30 Registration

SUNDAY MAY 18, 2008

07:30 – 08:30 Registration

08:30 – 09:30 Opening talks

SESSION S1 TUTORIALS I (IN MEMORIAM TOR HAGFORS)

Conveners C. Haldoupis and E. Kudeki

CHAIR VYTENIS VASYLIUNAS

09:30 – 09:50 W. Kofman (Invited) Tor Hagfors scientist and friend: his contribution to plasma physics and radar techniques

09:50 – 10:15 COFFEE BREAK

10:15 – 11:00 Page 41

D. T. Farley (Invited) The equatorial E region and its plasma instabilities: A tutorial

11:00 – 11:45 Page 41

R. F. Woodman (Invited) Spread F- An old equatorial aeronomy problem finally resolved?

11:45 – 12:30 Page 42

R. A. Vincent (Invited) Atmospheric waves and dynamics: A tutorial

12:30 END OF SESSION

12:30 – 15:00 LUNCH BREAK


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SESSION S2 TUTORIALS II

Conveners C. Haldoupis and E. Kudeki

CHAIR SHOIHIRO FUKAO

15:00 – 15:45 Page 43

M. C. Kelley (Invited) Mid-Latitude electrodynamics and plasma physics: A tutorial

15:45 – 16:30 Page 43

R. A. Heelis (Invited) Internal and external influences on ionospheric electrodynamics at low and middle latitudes

16:30 – 17:15 Page 44

U. S. Inan (Invited) Lower and middle atmospheric electrodynamics: A tutorial


18:30 – 20:00 WELCOME PARTY

20:00 END OF DAY (Sunday May 18)


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MONDAY MAY 19, 2008

SESSION S3 EQUATORIAL LOWER- AND MIDDLE- ATMOSPHERE STUDIES

Conveners G. Swenson, T. Nakamura, and J. Röttger

CHAIR GARY SWENSON

08:00 – 08:20 Page 45

K. Sato, Y. Kawatani, S. Watanabe, Y. Tomikawa, S. Miyahara, and M. Takahashi (Invited) Dynamics of the QBO and SAO revealed by a gravity-wave resolving GCM simulation

08:20 – 08:40 Page 46

P. Hoeg Tropical GPS atmosphere turbulence

08:40 – 09:00 Page 46

S. Kato MST radar observation ― capacity and limit ―

09:00 – 09:20 Page 47

M. Yamamoto, G. Hassenpflug, S. Saito, H. Luce, and S. Fukao (Invited) MU radar 1D, 2D, and 3D imaging of atmosphere and ionosphere

09:20 – 09:40 Page 48

R. Lieberman Variability of mesospheric diurnal tides and tropospheric diurnal heating during 1997—1998

09:40 – 10:00 Page 48

J. Meriwether (Invited) New results in mesospheric aeronomy studies: a review


CHAIR DAVE FRITTS

10:30 – 10:45 Page 49

A. F. Medeiros, M. J. Taylor, J. Fechine, H. Takahashi, R. A. Buriti, and L. M. Lima Twin mesospheric bores

10:45 – 11:00 Page 49

M. F. Larsen Magnetized Rossby waves as a possible driver for the lower E region neutral wind maximum

11:00 – 11:15 Page 50

D. Simonich and B. Clemesha First results from the São José dos Campos temperature LIDAR

11:15 – 11:30 Page 50

K. Cahoy Zonal structure in the equatorial ionosphere: both sides of the GPS radio occultation story

11:30 – 11:45 Page 51

K. Häusler and H. Lühr Wave-4 structure in the thermospheric zonal wind at dip equator latitudes as observed by CHAMP


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11:45 – 12:00 Page 52

G. Lehmacher, E. Kudeki, A. Akgiray, and J. Chau Radar cross-sections for mesospheric echoes at Jicamarca: measurements and estimates from turbulence theory

12:00 – 12:15 Page 52

G. D. Earle, A. M. Musumba, and S. L. Vadas In-situ evidence of nighttime midlatitude plasma density perturbations produced by gravity waves

12:15 – 12:30 Page 53

D. E. Rowland, R. F. Pfaff, and C. T. Steigies Combined impedance probe and Langmuir probe studies of the low-latitude E Region



SESSION S4 EQUATORIAL AND MID-LATITUDE MLT DYNAMICS

Conveners D. Pancheva, A. Smith, and J. Oberheide

CHAIR DORA PANCHEVA

14:00 – 14:20 Page 54

H.-L. Liu, J. Dudhia, and B. Kuo (Invited) Gravity wave distribution at low and mid-latitudes from the Nested Regional Climate Model

14:20 – 14:32 Page 54

B. R. Clemesha and P. P. Batista Seasonal variations in gravity wave activity at three at three locations in Brazil

14:32 – 14:44 Page 55

L.J. Gelinas , J.H. Hecht, R. Walterscheid, and R.G. Roble Seasonal and interannual variability of gravity waves at Adelaide and Alice Springs

14:44 – 14:56 Page 55

S. Vadas, J. Yue, C. She, H. Liu, D. Thorsen, T. Nakamura, and S. Reising Modeling the ring structures in the OH airglow layer from gravity waves excited by convection near Fort Collins, Colorado

14:56 – 15:08 Page 56

M. J. Taylor, D. Simkhada, J. B. Snively, and S. J. Franke Propagation and ducting of small-scale gravity waves in the mesospheric OH and O2 airglow emissions at low-latitudes

15:08 – 15:28 Page 56

R. M. Kaufmann, M. Ern, C. Lehmann, L. Hoffmann, M. Riese, C. V. Savigny, M. Lopez-Puertas, A. K. Smith, and D. R. Marsh (Invited) Long term variations and solar variability of atomic oxygen and hydrogen in the mesopause region

15:28 – 15:40 Page 57

U. Das and H. S. S. Sinha Long term variations in oxygen green line emission over Kiso from ground based observations using continuous wavelet transform


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15:40 – 15:52 Page 57

L. Hurd, M. F. Larsen, and A. Z. Liu Overturning instability in the mesosphere and lower thermosphere: analysis of instability conditions in lidar data from New Mexico and Hawaii

15:52 – 16:04 Page 58

J. Oberheide and J. M. Forbes Tidal propagation of deep tropical cloud signatures into the thermosphere from TIMED observations


CHAIR JENS OBERHEIDE

16:30 – 16:50 Page 58

W.E. Ward, J. Du, D.Y Wang, and the CAWSES Tidal Campaign Team (Invited) Tidal characteristics from the Extended Canadian Middle Atmosphere Model and comparisons with CAWSES tidal campaign results

16:50 – 17:02 Page 59

N. Grieger, U. Achatz, H. Schmidt, and W. Singer Thermal tides as important coupling process in the atmosphere

17:02 – 17:14 Page 60

R. Lieberman, J. Oberheide, D. Riggin, and R.Stockwell Estimates of momentum deposition on the diurnal tide

17:14 – 17:26 Page 60

D. Pancheva, P. Mukhtarov, and B. Andonov Planetary waves and tides observed by TIMED/SABER in coupling the stratosphere-mesosphere-lower thermosphere during the major stratospheric warming in 2003/2004

17:26 – 17:38 Page 61

W. Singer, P. P. Batista, J. Oberheide, T. Nakamura, P. Hoffmann, B. R. Clemesha, R. A. Buriti, D. Riggin, and G. Ramkumar Mesospheric/lower thermospheric winds, tides and mesopause temperatures at low latitudes from meteor radar and satellite observations

17:38 – 17:50 Page 61

L. Guo and G. Lehmacher Equatorial middle atmosphere wind observations with the Jicamarca meteor radar

17:50 – 18:02 Page 62

C. Haldoupis On the seasonal dependence of midlatitude Sporadic E layers

18:02 – 18:14 Page 62

T. Maruyama, S. Saito, M. Kawamura, and K. Nozaki Thermospheric meridional winds as deduced from ionosonde network and midnight temperature maximum

18:14 – 18:26 Page 63

J. Clemmons The equatorial thermospheric anomaly: update on analysis of measurements from the ionization gauge on the Streak mission



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POSTER P1 POSTERS FOR SESSIONS S3 AND S4

Conveners G. Swenson and D. Pancheva

Time:

Author Attendance :

All day Monday and Tuesday, May 19-20

Coffee breaks, 13:00 – 14:00 and 19:00 to 20:00

POSTER CHAIR GERALD LEHMACHER AND DENNIS RIGGIN

S3 - P1- 01 Page 64

J. O. Adeniyi, S. M. Radicella, I. A. Adimula, O. A. Oladipo, O. Olawepo, and A. A. Willoughby Analysis of March 29 2006 eclipse on the E and F1 region at Ilorin

S3 - P1- 02 Page 64

H. C. Aveiro, C. M. Denardini, and M. A. Abdu Planetary waves in the equatorial electrojet obtained by wavelet analysis of magnetometer data

S3 - P1- 03 Page 64

M.A. Ayoola, G. I. Olatona, E. O. Oladiran, and J. A. Adedokum The March 29, 2006 solar eclipse as observed at Ibadan, Nigeria

S3 - P1- 04 Page 65

R. A. Buriti, W. K. Hocking, P. P. Batista, A. F. Medeiros, and B. R. Clemesha Observations of zonal and meridional winds and diurnal and semidiurnal tides at 7.4°S by a meteor radar

S3 - P1- 05 Page 65

M. Devi, A. K. Barbara, Yu. Ruzhin, A. Depueva, and V. Depuev Role of equatorial anomaly in assertion of low latitude earthquake-perturbations on ionosphere

S3 - P1- 06 Page 66

G. K. Kumar, M. V. Ratnam, A. K. Patra, S. V. B. Rao, K. K. Kumar, S. Gurubaran, G. Ramkumar, and D. N. Rao Climatology of low-latitude mesospheric dynamics using Gadanki VHF radar, rocket, and HRDI

S3 - P1- 07 page 67

H. S. S. Sinha, U. Das, R. N. Misra, M. B. Dadhania, S. Banerjee, and N. Dutt Study of mesospheric turbulence using rocket-borne electron density measurements

S3 - P1- 08 page 67

C. M. Wrasse, J. Fechine, H. Takahashi, A. F. Medeiros, J. V. Bageston, and C. M. Denardini Gravity waves sources in the Brazilian equatorial region during SpreadFEX Campaign

S3 - P1- 09 page 68

C. M. Wrasse, H. Takahashi, J. Fechine, A. F. Medeiros, J. Wickert, and C. M. Denardini Gravity waves activities in the stratosphere and mesosphere over the Brazilian equatorial region

S4 - P1- 10 page 69

L. M. Lima, H. Takahashi, B. R. Clemesha, P. P. Batista, and C. M. Wrasse A comparative study of the quasi-2-day wave observed at 7.4°S and 22.7°S, Brazil, during summertime


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20:00 END OF POSTER SESSION

20:00 – 21:00 Page 70

ISEA SPECIAL LECTURE OF GENERAL INTEREST

J. H. Seiradakis The Antikythira Mechanism

21:00 END OF DAY (Monday May 19)


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TUESDAY MAY 20, 2008

SESSION S5 E-REGION PLASMA PHYSICS

Conveners J.-P. St.-Maurice, A. K. Patra, and C. De Nardini

CHAIR JEAN-PIERRE ST.- MAURICE

08:00 – 08:15 Page 70

D. L. Hysell, G. Michhue, M. F. Larsen, R. Pfaff, and J. L. Chau (Invited) Lessons learned observing Farley Buneman waves at low, middle, and high latitudes

08:15 – 08:27 Page 71

L. M. Kagan and R.S. Kissack Inelastic electron energy exchange and altitude behaviour of a phase velocity spectrum of Farley-Buneman waves for equatorial electrojet

08:27 – 08:39 Page 72

J.-P. St.-Maurice The speed of type I and other fast moving echoes in the ionospheric E region

08:39 – 08:51 Page 73

D. Kovalev, A. Smirnov, and Y. Dimant Hybrid-model simulations of Farley-Buneman instability with electron thermal effects

08:51 – 09:03 Page 73

M. M. Oppenheim, Y. S. Dimant, and L. P. Dyrud Large-scale simulations of Farley-Buneman turbulence in 2D and 3D

09:03 – 09:18 Page 74

R. K. Choudhary and J.-P. St.-Maurice (Invited) What two-step Type I waves reveal about equatorial E region turbulence

09:18 – 09:30 Page 75

R. R. Ilma, M. C. Kelley, and J. L. Chau Intense stormtime equatorial electric fields and evidence for anomalous resistivity in the electrojet

09:30 – 09:42 Page 75

P. Muralikrishna and V. H. Kulkarni The effect of dust particles on the growth time and amplitude of type I and type II irregularities in the E-region

09:42 – 09:54 Page 76

F. Lu, D. T. Farley, and W. E. Swartz Aspect angle measurements of irregularities in the equatorial E region above Jicamarca

09:54 – 10:06 Page 76

C. M. Denardini, M. A. Abdu, H. C. Aveiro, P. D. S. C. Almeida,L. C. A. Resende, Ê. P. A. Olívio, J. H. A. Sobral, and C. M. Wrasse Counter electrojet features in the Brazilian sector: simultaneous observation on radar, digital sounder and magnetometers data



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CHAIR A. K. PATRA

10:30 – 10:45 Page 77

R. T. Tsunoda (Invited) Irregularities in the low- and mid-latitude E region: A historical perspective

10:45 – 10:57 Page 77

A. Bourdillon, P. Dorey, and S. Saillant Quasi-periodic variation of the sporadic E layer reflection

10:57 – 11:09 Page 77

N. V. Rao, A. K. Patra, and S. V. B. Rao Some intriguing features of QP echoes revealed by Gadanki radar observations and a mechanism that explains them

11:09 – 11:21 Page 78

A. K. Patra, N. V. Rao, T. Yokoyama, Y. Otsuka, and M Yamamoto Intriguing details of 150-km radar echoes revealed by off-equatorial observations made from Gadanki and Kototabang

11:21 – 11:33 Page 78

R. T. Tsunoda and W. L. Ecklund 150 km echoes: Recent results from the Pacific sector

11:33 – 11:48 Page 80

L. Dyrud, M. Oppenheim, E. Kudeki, S. Close, and D. Janches (Invited) The formation, evolution and radar reflection from meteor trail plasma irregularities

11:48 – 12:00 Page 80

A. Malhotra, J. D. Mathews, and J. Urbina Multi-Static Common Volume Radar Observations of Meteor Echoes at Jicamarca

12:00 – 12:12 Page 81

E. Bass, M. Oppenheim, G. Sugar, and J. Chau Meteor Observations as a Method of Determining Atmospheric Properties

12:12 – 12:24 Page 81

S. P. Gupta Plasma waves induced by meteors in equatorial E region - rocket borne results of Leonid meteor shower of Nov. 1999



SESSION S6 F-REGION PLASMA IRREGULARITIES: CAUSES AND EFFECTS

Conveners A. Bhattacharyya, R. Woodman, and M. A. Abdu

CHAIR ARCHANA BHATTACHARYYA

14:00 – 14:15 Page 83

E. Kudeki, A. Akgiray, M. Milla, J. L. Chau, and D. L. Hysell (Invited) Initiation of equatorial Spread F

14:15 – 14:27 Page 83

M. A. Abdu Equatorial spread F irregularity development conditions as diagnosed from conjugate point observations by digisondes and all-sky imagers in Brazil


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14:27 – 14:39 Page 83

R. T. Tsunoda On the role of large-scale wave structure in the initiation of equatorial plasma bubbles

14:39 – 14:51 Page 84

C. Stolle, H. Lühr, B. Fejer, and J. Jensen Relation between ESF occurrence rate and prereversal plasma drift velocity

14:51 – 15:06 Page 84

B. G. Fejer (Invited) Longitude dependent electrodynamic effects on equatorial F-Region plasma irregularities

15:06 – 15:18 Page 85

Y. Otsuka, T. Ogawa, and Effendy VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia

15:18 – 15:30 Page 85

J. Krall, J. D. Huba, and G. Joyce Three-dimensional simulation of equatorial Spread-F with meridional winds

15:30 – 15:42 page86

R. Pfaff, C. Liebrecht, J.-J. Berthelier, M. Parrot, and J.-P. Lebreton DEMETER observations of highly structured plasma density and associated ELF electric field and magnetic field irregularities at Middle and low latitudes

15:42 – 15:54 Page 86

L. Sidorova Topside plasma bubbles, seen as He+ density depletions, and thermosphere meridional wind influence


CHAIR MANGALATHAYIL ALI ABDU

16:25 – 16:40 Page 87

S. Fukao and M. Yamamoto (Invited) New aspects of mid-latitude plasma plumes revealed by radio and optical observations

16:40 – 16:52 Page 88

S. Sripathi, S. Bose, A. K. Patra, T. K. Pant, B. Kakad, and A. Bhattacharyya Observations of ESF irregularities using simultaneous radar and GPS over Indian region

16:52 – 17:04 Page 89

H. Takahashi, A. F. Medeiros, C. M. Wrasse, M. J. Taylor, P.-D. Pautet, D. Gobbi, J. Fechine, M. A. Abdu, I. S. Batista, E. Paula, J. H. A. Sobral, D. Arruda, and D. Fritts Optical observation of ionospheric plasma bubbles and mesospheric gravity

17:04 – 17:16 Page 89

T. Ogawa, Y. Miyoshi, Y. Otsuka, and T. Nakamura Relationship between GPS ionospheric scintillation occurrence over Indonesia and equatorial atmospheric waves

17:16 – 17:28 Page 90

T. Kikuchi, K. K. Hashimoto, Y. Tsuji, S. Watari, and B. Fejer Stormtime convection and overshielding electric fields at the equator as observed with magnetometers and incoherent scatter radar


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17:28 – 17:40 Page 90

E. S. Miller, J. J. Makela, R. L. Bishop, and P. R. Straus Multi-year study of the altitude distribution of scintillation-causing irregularities and gradients

17:40 – 17:52 Page 91

A. Bhattacharyya and B. Kakad Evolution of intermediate scale length equatorial spread F irregularities

17:52 – 18:04 Page 91

J. A. Whalen The linear dependence of L-band scintillation on electron density observed in the anomaly

18:04 – 18:16 Page 92

E. A. Kherani, E. R. de Paula, M. T. A. H. Muella, A. A. N. Campos, L. F. C. de Rezende, and P. F. Smorigo The large TEC fluctuations near the equatorial ionization anomaly during the equatorial spread F: observation from the GPS network over Brazil and simulation

18:16 – 18:28 Page 92

P. C. Anderson and P. R. Straus GPS occultation observations of equatorial scintillation: dependence on magnetic field orientation, longitude, and season



Conveners J.-P. St-Maurice and A. Bhattacharyya

Time:

Author Attendance :

All day Monday and Tuesday, May 19-20


POSTER CHAIR ALAIN BOURDILLON AND GLENN HUSSEY

S5 - P2- 01 Page 93

V. Belyey, C. La Hoz, J. Chau, and H. Pinedo First 3-dimensional radar interferometry observations of equatorial E region irregularities at Jicamarca

S5 - P2- 02 Page 93

J. L. Chau, R. F. Woodman, and M. A. Milla Perpendicular and off-perpendicular to B observations of 150-km echoes: evidence of meridional modulation and structure

S5 - P2- 03 Page 94

E. A. Kherani, E. R. de Paula, and F. C. de Meneses Jr. The possible role of inter-hemispheric-field-aligned current for the generation of 150-km echoes

S5 - P2- 04 Page 94

L. M. Kagan, R. S. Kissack, M. C. Kelley, and R. A. Cuevas Unexpected rapid decrease in phase velocity of sub-meter Farley-Buneman waves with altitude

S5 - P2- 05 Page 95

C. M. Denardini, M. A. Abdu, J. H. A. Sobral, C. M. Wrasse, H. C. Aveiro, P. D. S. C. Almeida, L. C. A. Resende, and Ê. P. A. Olívio EEJ Features Based on Coherent Radars Soundings in the Brazilian Sector


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S5 - P2- 06 Page 96

R. Pfaff Comparative in situ measurements of plasma instabilities in the equatorial and auroral electrojets

S5 - P2- 07 Page 97

G.C. Hussey, C. Meek, C. Haldoupis, A. Bourdillon, and J. Delloue Neutral winds in the mid-latitude E-region as deduced from coherent backscatter radar plasma irregularity observations

S5 - P2- 08 Page 97

M. F. Larsen, D. L. Hysell, S. M. Smith, J. Friedman, Q. H. Zhou, and R. L. Bishop Evidence of neutral wind drivers for quasi-periodic echo structures in sporadic E layers based on observations from St. Croix and Puerto Rico

S5 - P2- 09 Page 98

N. V. Rao, A. K. Patra, and S. V. B. Rao Low altitude Quasi-Periodic (LQP) echoes studied using long term Gadanki radar observations

S5 - P2- 10 Page 99

S. P. Gupta Differences in the nature of E-region irregularities at the magnetic equator and at 6oN of magnetic equator

S5 - P2- 11 Page 99

S. Shalimov and T. Ogawa On possible mechanisms of altitude-extended field-aligned irregularities (FAI), associated with quasi-periodic (QP) radar echoes

S5 - P2- 12 Page 100

L. N. Lomidze and G. G. Didebulidze Formation and behaviour of sporadic E layers under the influence of vortical-type perturbation excited in the horizontal shear flow

S5 - P2- 13 Page 100

C. Arras, J. Wickert , C. Jacobi, S. Heise, G. Beyerle, T. Schmidt, and M. Rothacher Sporadic E layer climatology derived from CHAMP, GRACE and COSMIC radio occultations – initial results from GFZ Potsdam

S5 - P2- 14 Page 101

D. Kouba, P. Šauli, J. Boška, and O. Santolík E-region ionospheric drift measurements during sporadic E-layer occurrence using Digisonde DPS-4

S5 - P2- 15 Page 102

D. V. Phanikumar, A. K. Patra, K. Kishorekumar, and G. Yellaiah Seasonal variations of low-latitude sporadic-E and field aligned irregularities and their relation to sporadic meteor flux

S5 - P2- 16 Page 102

A. Malhotra, J. D. Mathews, and J. Urbina Sporadic-E observations at Jicamarca?!

S5 - P2- 17 Page 103

Y. S. Dimant, and M. M. Oppenheim Meteor plasma trails in E region: diffusion, electric fields, and ionospheric disturbances

S5 - P2- 18 Page 103

G. Sugar, M. Oppenheim, E. Bass, Y. Dimant, and J. Chau Meteor trails in the ionosphere: day/night and altitude differences

S6 - P2- 19 Page 105

F. C. de Meneses, P. Muralikrishna, and E. A. Kherani The simultaneous rocket observation of electron density and temperature inside the equatorial spread-F bubble and their numerical simulation


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S6 - P2- 20 Page 105

L. Biktash The solar wind and geomagnetic storm effects on generation of the equatorial scintillation

S6 - P2- 21 Page 106

C. M. N. Candido, A. A. Pimenta, C. M. Wrasse, Y. Sahai, and F. Becker-Guedes Observation of MSTIDs in the Brazilian sector possibly associated with troposhperic disturbances at mid-latitudes

S6 - P2- 22 Page 106

S. L. England, T. J. Immel, S. H. Park, H. U. Frey, and S. B. Mende A study of the mean properties of equatorial ionospheric plasma depletion drift velocities determined from far-ultraviolet spacecraft observations

S6 - P2- 23 Page 107

J. D. Huba and G. Joyce Three-dimensional equatorial Spread F modeling

S6 - P2- 24 Page 107

M. Ishii, T. Maruyama, and I. Kimura Characteristics of anomaly of HF radio wave arrival direction observed near the evening terminator

S6 - P2- 26 Page 108

A. T. Karpachev Peculiar properties of the topside ionograms at the equatorial latitudes

S6 - P2- 26 Page 108

L. Liu, M. He, W. Wan, and M.-L. Zhang An analysis of the lower topside ionospheric scale heights based on the electron density profile retrieved from FORMOSAT/COSMIC radio occultation measurements

S6 - P2- 27 Page 109

C. Martinis, J. Baumgardner and M. Mendillo The Simultaneous occurrence of airglow structures associated with ESF and MSTIDs in the Southern Hemisphere

S6 - P2- 28 Page 109

T. Maruyama, S. Saito, M. Kawamura and K. Nozaki Onsets of equatorial plasma bubble and ionosphere-thermosphere system

S6 - P2- 29 Page 110

M. Mascarenhas, E. A. Kherani, J. H. A. Sobral and E.R. de Paula Dynamical simulation of electromagnetic Spread F

S6 - P2- 30 Page 110

M. Mendillo, J. Niehof, K. Garcia, C. Prested, S. McGregor, N. Viall, L. Moore, P. Withers, C. Martinis, and A. Stephan Can equatorial Spread-F (ESF) occur on other planets?

S6 - P2- 31 Page 111

H. Nakata, Y. Kinoshita, Y. Otsuka, T. Takano, S. Shimakura, K. Shiokawa, and T. Ogawa Reception of TV broadcast radio waves associated with equatorial plasma bubbles

S6 - P2- 32 Page 111

M. Nishioka, A. Saito, and T. Tsugawa Occurrence characteristics of plasma bubble studied with global ground-based GPS receiver networks

S6 - P2- 33 Page 112

J. Park, C. Stolle, H. Luhr, and M. Rother Magnetic signatures of plasma blobs as observed by the CHAMP satellite


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S6 - P2- 34 Page 113

A. A. Pimenta, C. M. N. Candido, D. C. M. Amorim, Y. Sahai, J. A. Bittencourt, P. R. Fagundes, and D. Gobbi Relevant aspects of thermospheric dark band structures observed by ground-based optical and radio techniques over the Brazilian low-latitude sector under different solar activity conditions

S6 - P2- 35 Page 113

H. Pinedo, J. L. Chau, and D. L. Hysell Using JULIA long dataset to find preconditioning evidence of ESF in bottom-type layers

S6 - P2- 36 Page 114

L. Sidorova Plasma bubbles in the topside ionosphere: high solar activity period

S6 - P2- 37 Page 115

S. Sripathi, S. Bose, and A. Bhattacharyya Morphological study of equatorial plasma bubbles using GPS L-band scintillations over Indian region

S6 - P2- 38 Page 115

D. Tiwari, B. Kakad, S. Sripathi, T.K. Pant, and A. Bhattacharyya Magnetic activity effects on ESF irregularities: case studies

S6 - P2- 39 Page 116

S. Vadas and H. Liu Neutral and Plasma variability in the F region from the dissipation of gravity waves from convection

S6 - P2- 40 Page 116

J.A. Whalen Temporal and spatial regularities in the post-sunset equatorial anomaly, and their significance to scintillation


20:00 END OF DAY (Tuesday May 20)


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WEDNESDAY MAY 21, 2008

FULL DAY EXCURSION

PROGRAM

Group A

08:45 Start from the Hotel

09:30 –11:30 Visit Minoan Palace at Malia, and Kremasta Monasteri near Neapolis

12:00 Meet with group B at Elounda

Group B (morning tour is longer and more tiring)

08:30 Start from the Hotel

09:30 – 11:00 Visit Lasithi Plateau and Dikteon Andron

12:00 Meet with group A at Elounda

Group A and B

12:00 – 14:00 Boat trip to Spinaloga Island

14:00 – 16:00 Lunch at tavernas by the sea at the village of Plaka

16:00 – 17:00 Return by boat to Agios Nikolaos and spend there an hour

19:00 Arrive back to the Hotel

19:00 END OF DAY (Wednesday May 21)


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THURSDAY MAY 22, 2008

SESSION S7 IONOSPHERIC ELECTRODYNAMICS: THEORY AND NUMERICAL MODELING

Conveners C. Fesen, J. Huba, and T. Fuller-Rowell

CHAIR CASSANDRA FESEN

08:00 – 08:15 Page 118

V. Vasyliūnas and P. Song Do electric fields drive ionospheric plasma flows?

08:15 – 08:30 Page 118

J. D. Huba (Invited) Electrodynamics of the thermosphere-ionosphere-magnetosphere system

08:30 – 08:45 Page 119

M. Mendillo, H. Rishbeth, R. Roble, J. Wroten, and B. Foster (Invited) Approaches to the study of non-electrodynamical sources of ionospheric variability at equatorial and low latitudes

08:45 – 09:00 Page 119

C. H. Lin, A. D. Richmond, G. J. Bailey, and J. Y. Liu (Invited) Redistribution of the low-latitude ionospheric plasma structure during a major magnetic storm

09:00 – 09:15 Page 120

N. Maruyama, T. Fuller-Rowell, M. Codrescu, D. Anderson, A. Richmond, A. Maute, S. Sazykin, F. Toffoletto, R. Spiro, R. Wolf, and G. Millward (Invited) Low latitude storm time electric fields and their role in the coupled thermosphere-ionosphere-plasmasphere system

09:15 – 09:30 Page 121

M.V. Klimenko, V.V. Klimenko, and V.V. Bryukhanov Ionosphere electrodynamics and its influence on the equatorial anomalies

09:30 – 09:45 Page 121

J. Uemoto, T. Ono, T. Maruyama, S. Saito, M. Iizima, and A. Kumamoto Observations and model calculations of stratification of the F2 layer in the equatorial ionosphere

09:45 – 10:00 Page 122

N. Balan, H. Alleyne, S. V. Thampi, K. Lynn, Y. Otsuka, B. G. Fejer, and M. A. Abdu F3 layer during penetration electric field


CHAIR JOE HUBA

10:30 – 10:45 Page 123

X. Pi, V. Akopian, A. Komjathy, B. D. Wilson, A. J. Mannucci, B. A. Ijima, and M. A. Dumett Modeling low-latitude ionosphere using GAIM assimilating GPS data


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10:45 – 11:00 Page 123

M. C. Kelley, J. Retterer, O. de La Beaujardière, and H. Kil Assimilation of ROCSAT equatorial electric field data into the AFRL C/NOFS model

11:00 – 11:15 Page 124

P. Alken and S. Maus Estimating electric fields in the equatorial ionosphere from CHAMP observations

11:15 – 11:30 Page 124

D. Anderson, E. Araujo-Pradere, A. Anghel, K. Yumoto, A. Bhattacharyya, M. Hagan, A. Maute, and L. Scherliess Quantifying the daytime, equatorial ExB drift velocities associated with the 4-cell, non-migrating tidal structure

11:30 – 11:45 Page 125

W. Wan, J. Xiong, L. Liu, M.-L. Zhang, F. Ding, and B. Ning Diurnal, seasonal and solar cycle variations of the longitudinal wavenumber-4 patterns at low latitude ionosphere

11:45 – 12:00 Page 125

T. W. Fang, A. D. Richmond, H. Kil, G. Millward, and J. Y. Liu Model simulation of longitudinal density structure in the equatorial ionosphere

12:00 – 12:15 Page 126

H. Kil, S.–J. Oh, and L. J. Paxton The effect of the daytime ExB drift, interhemispheric winds, and pre-reversal enhancement on the formation of longitudinal density structure

12:15 – 12:30 Page 127

T. Bösinger, E. N. Ermakova, and C. Haldoupis Search for magnetic inclination effects at low latitude in the spectral resonance structures of the ionospheric Alfvén resonator



SESSION S8 COUPLING PROCESSES AT LOW- AND MID-LATITUDES

Conveners M. Larsen, K. Shiokawa, and R. Cosgrove

CHAIR MIGUEL LARSEN

14:00 – 14:15 Page 128

H. Lühr and P. Ritter (Invited) Response of the low-latitude ionosphere-thermosphere system to high-latitude activity

14:15 – 14:27 Page 128

R. Hedden, L. Waldrop, and J. Meriwether Variations of thermospheric [O] composition during a magnetic storm event

14:27 – 14:39 Page 128

J. Meriwether, M. Faivre, C. Fesen, and O. Veliz New results on equatorial thermospheric dynamics and the midnight temperature maximum

14:39 – 14:51 Page 129

C. G. Fesen, R. G. Roble, and H. Liu Simulations of the midnight temperature maximum with the NCAR TIME-GCM


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14:51 – 15:03 Page 130

T. K. Ramkumar Equatorial mesospheric planetary wave signatures in the equatorial electrojet

15:03 – 15:18 Page 131

S. Vadas (Invited) Penetration of gravity waves into the F region from the lower atmosphere at low and mid latitudes

15:18 – 15:30 Page 131

D. C. Fritts, and SpreadFEx colleagues Indications of gravity wave scales, amplitudes, and influences in the thermosphere and ionosphere from the Spread F Experiment (SpreadFEx)

15:30 – 15:42 Page 131

R. L. Bishop and P. Straus Equatorial and mid-latitude scintillation initiated from tropical storms, hurricanes, and typhoons

15:42 – 15:54 Page 132

C. Arras, J. Wickert, C. Jacobi, S. Heise, G. Beyerle, T. Schmidt, and M. Rothacher Semidiurnal tidal signature in sporadic E occurrence rates derived from GPS radio occultation measurements at mid-latitudes


CHAIR KAZUO SHIOKAWA

16:24 - 16:36 Page 132

R. Cosgrove Neutral wind, sporadic E layer, and F layer coupling in the nighttime mid-latitude ionosphere

16:36 - 16:48 Page 133

J. Younger, I.M. Reid, and R.A. Vincent Observations of meteor trail diffusion using VHF radar

16:48 – 17:00 Page 133

J. D. Mathews, D. Livneh, I. Seker, F. T. Djuth Quasi-Periodic F-region MSTIDs at Arecibo: a magnetospheric link?

17:00 – 17:12 Page 134

J. Urbina, E. Kudeki, S. Franke, and R. Pfaff Analysis of meter-scale E-region plasma density irregularities from North Carolina and Puerto Rico

17:12 – 17:24 Page 134

R. Pfaff, C. Liebrecht, J. Urbina, and E. Kudeki Daytime observations of mid-latitude Sporadic-E and QP radar echoes

17:24 – 17:36 Page 135

G. Swenson and A. Liu Large amplitude waves at mid and low-latitude mesosphere; a summary of observations

17:36 – 17:48 Page 135

C. Martinis, M. Mendillo, and J. Baumgardner Unusual 630.0 nm airglow variations at midlatitudes

17:48 – 18:04 Page 136

T. Adachi, Y. Takahashi, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, and H. U. Frey (Invited) Transient luminous events as lightning effects in the lower ionosphere: Recent progresses by ISUAL measurements on FORMOSAT-2 satellite

18:04 – 18:16 Page 137

O. Chanrion, T. Neubert, and H. Stenbaek-Nielsen Particle simulations of optical emissions in sprite streamers


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18:16 – 18:28 Page 137

J. Lastovicka, D. Buresova, J. Chum, and T. Sindelarova Investigations of effects of infrasound on the ionosphere



Conveners C. Fesen and M. Larsen

Time:

Author Attendance :

All day Thursday and Friday, May 22-23


POSTER CHAIR RUSSEL COSGROVE AND TATSUHIRO YOKOYAMA

S7 - P3- 01 Page 138

M. V. Klimenko, V. V. Klimenko, and V. V. Bryukhanov The behavior of the TEC and equatorial electrojet during April 8, 2005 solar eclipse

S7 - P3- 02 Page 138

M. V. Klimenko, V. V. Klimenko, and V. V. Bryukhanov Effects of substorms with different moments of the beginning in equatorial electrojet and parameters of F-region of Equatorial Ionosphere

S7 - P3- 03 Page 139

A. A. Namgaladze, M. V. Klimenko, V. V. Klimenko, and I. E. Zakharenkova Forming of the ionospheric precursors of the earthquakes by zonal electric field

S7 - P3- 04 Page 140

A. B. Rabiu Comparative study of some parameters of equatorial electrojet in West African and Indian sectors

S8 - P3- 05 Page 141

H. Lühr, M. Rother, K. Häusler, P. Alken, and S. Maus The effect of non-migrating tides on the equatorial electrojet

S8 - P3- 06 Page 141

T. Yokoyama, Y. Otsuka, M. Yamamoto, and D. L. Hysell Study on the Perkins instability by E-F coupled three-dimensional simulation model

S8 - P3- 07 Page 142

W. E. Swartz, M. C. Kelley, and N. Aponte E and F region coupling between an intense sporadic E layer, an MSTID, and a neutral atom layer

S8 - P3- 08 Page 142

A. K. Patra, N. V. Rao, N. Dashora, T. K. Pant, and K. Niranjan Perspectives of electrostatic coupling on various manifestations of low-latitude E and F region irregularities related to equatorial plasma bubble studied in the Indian sector

S8 - P3- 09 Page 143

P. A. Bernhardt, J. Werne, and M. F. Larsen Simulations of strong wind shears in the mesosphere and their effects on structure of the E-Layer


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S8 - P3- 10 Page 144

T. Ogawa, N. Nishitani, Y. Otsuka, K. Shiokawa, T. Tsugawa, and A. Saito E- and F-region coupling revealed by nighttime MSTID and sporadic E layer observations with the mid-latitude SuperDARN Hokkaido radar

S8 - P3- 11 Page 144

S. Shalimov, T. Ogawa, and Y. Otsuka On the instability of sporadic E layer formation under vortical neutral wind motion at mid-latitude

S8 - P3- 12 Page 145

T. Sindelarova, D. Buresova, and J. Chum Observations of acoustic-gravity waves in the ionosphere generated by severe tropospheric weather

S8 - P3- 13 Page 145

N. Christakis, C. Haldoupis, Q. Zhou, and C. Meek Variability and descent of mid-latitude sporadic E layers at Arecibo

S8 - P3- 14 Page 146

S. Watanabe, H. Liu, and M-Y. Yamamoto Ionosphere-thermosphere coupling in low latitude region

S8 - P3- 15 Page 147

E. R. Talaat , J.-H. Yee, L. J. Paxton, J. Russell III, M. G. Mlynczak, R. DeMajistre, and A. Christensen Inter-annual and long-term variations observed in the ITM system

S8 - P3- 16 Page 147

S. Sripathi, S. Bose, D. Tiwari, and A. Bhattacharyya On the linking of large-scale wave like modulations in the TEC to the EEJ strength over India: Is it due to planetary scale waves?

S8 - P3- 17 Page 148

J. Xiong, W. Wan The 7-day planetary wave oscillations in the ionosphere and MLT revealed by TEC, UKMO and AURA

S8 - P3- 18 Page 148

E. Pacheco and R. Heelis Variability of vertical drifts during storm-times at equatorial latitudes

S8 - P3- 19 Page 149

L. Bankov, M. Parrot, R. Heelis, J-J. Berthelier, and A. Vassileva Longitudinal signatures of tidal influence on topside ionosphere at low latitudes by means of DEMETER and DMSP-f15 data

S8 - P3- 20 Page 149

E. Astafyeva, K. Heki, E. Afraimovich, V. Kiryushkin, and S. Shalimov Evolution of ionospheric disturbances generated by large earthquakes

S8 - P3- 21 Page 150

N. Ambrosiadi, C. Haldoupis, and A. Mika More observations for testing the relationsphip between Sprites and subionospheric Early VLF signal perturbations

S8 - P3- 22 Page 151

E. A. Kherani, P. Lognonne, H. Herbert, and G. Occhipinti The Sumatra tsunami induced ionospheric signatures from the CHAMP satellite: a manifestation of atmosphere-ionosphere coupling via acoustic-gravity waves

S8 - P3- 23 Page 152

M. Devi , A. K. Barbara , Yu. Ruzhin , A. Depueva , and V. Depuev Role of equatorial anomaly in assertion of low latitude earthquake-perturbations on ionosphere


20:00 – 23:30 GALA DINNER – Aldemar Knossos Hotel

23:30 END OF DAY (Thursday May 22)


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FRIDAY MAY 23, 2008

SESSION S9 NEW TECHNIQUES, EXPERIMENTS, CAMPAIGNS, AND RESULTS

Conveners D. Hysell, J. Clemmons, and M. Mila

CHAIR DAVE HYSELL

08:00 – 08:15 Page 153

G. D. Earle, J. H. Klenzing, P. A. Roddy, and E. L. Patrick (Invited) The new C/NOFS neutral wind instruments: laboratory and flight validation results

08:15 – 08:30 Page 153

C. Coker, K. F. Dymond, S. A. Budzien and D. Chua COSMIC observations of the equatorial ionosphere

08:30 – 08:45 Page 154

J. Comberiate and L. J. Paxton Coordinated UV imaging of equatorial plasma bubbles using TIMED/GUVI and DMSP/SSUSI

08:45 – 09:00 Page 154

K. S. Kalogerakis, T. G. Slanger, and E. A. Kendall Remote oxygen sensing by ionospheric excitation (ROSIE)

09:10 – 09:15 Page 155

T. J. Immel, S.L. England, J. M. Forbes, J. D. Huba, M. E. Hagan, and R. DeMajistre (Invited) Space-based studies of low-latitude ionospheric forcing originating in the lower atmosphere

09:15 – 09:30 Page 155

J. H. Klenzing, G. D. Earle, R. A. Heelis, and W. R. Coley Effects of non-ideal biased grids on geophysical parameters obtained from RPA data

09:30 – 09:45 Page 156

A. Saito and IMAP working group Plan of imaging observation of the mesosphere, ionosphere, and plasmasphere by ISS-IMAP mission

09:45 – 10:00 Page 156

C. E. Valladares, J. L. Chau, J. V. Eccles, and R. F. Woodman The Low-latitude Ionospheric Sensor Network (LISN)


CHAIR JIM CLEMMONS

10:30 – 10:45 Page 157

M. Milla and E. Kudeki

Modeling the incoherent scatter radar spectrum perpendicular r B

10:45 – 11:00 Page 158

D. L. Hysell, F. S. Rodrigues, J. L. Chau, and J. D. Huba Full profile incoherent scatter analysis at Jicamarca

11:00 – 11:15 Page 158

P. Reyes, M. Milla, and E. Kudeki Incoherent scatter measurements of F-region temperatures with the Jicamarca radar beam pointing perpendicular to B


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11:15 – 11:30 Page 159

T. Yokoyama, M. Yamamoto, Y. Otsuka, A. K. Patra, S.-Y. Su, S. Fukao, and D. L. Hysell (Invited) Recent progress in studying equatorial and low-latitude irregularities with Equatorial Atmosphere Radar

11:30 – 11:45 Page 160

C. L. Siefring and P. A. Bernhardt First results on studies of the low latitude ionosphere with the CITRIS beacon receiver on STPSAT1

11:45 – 12:00 Page 161

J. J. Makela, J. W. Meriwether, E. S. Miller, and S. J. Armstrong (Invited) New optical experiments for studying equatorial irregularities

12:00 – 12:15 Page 162

G. Swenson, C. Carlson, L. Waldrop, and P. Dragic A thermospheric lidar for He 1083 nm, density and Doppler measurements

12:15 – 12:30 Page 162

M.-Y. Yamamoto, Y. Yokoyama, H. Habu, T. Abe, S. Watanabe, M. Yamamoto, Y. Otsuka, A. Saito, T. Ono, and M. Nakamura WIND rocket campaign: Lithium release experiment in evening midlatitude thermosphere


SESSION S10 IONOSPHERIC STORMS AND SPACE WEATHER EFFECTS

Conveners R. Pfaff, L. Paxton, and D. Pallamraju

CHAIR ROB PFAFF

13:50 – 14:00 Page 164

S. Gadimova The United Nations and International Committee on Global Navigation Satellite Systems: World-wide ground-based instrument arrays

14:00 – 14:15 Page 164

J. C. Foster (Invited) Ionospheric storm fronts at low and mid latitudes

14:15 – 14:30 Page 165

E. Astafyeva Ionosphere TEC response to geomagnetic storms: seasonal and longitudinal features

14:30 – 14:45 Page 166

L. Biktash, T. Maruyama, and K. Nozaki The solar wind control of the equatorial ionosphere dynamics during geomagnetic storms

14:45 – 15:00 Page 166

Y.O. Migoya Orué, S. M. Radicella, and P. Coïsson Low latitude ionospheric effects of major geomagnetic storms observed using TOPEX TEC data

15:00 – 15:15 Page 167

Y. Goi, A. Saito, M. Nishioka, and T. Tsugawa Vertical distribution of electron density derived from TEC data of the GRACE satellite and the ground-based GPS receivers at mid- and low-latitudes

15:15 – 15:30 Page 167

W. J. Burke (Invited) Some Consequences of Stormtime, Global Energy Budgets


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15:30 – 15:45 Page 168

A. M. Hasbi, M. Alauddin Mohd Ali, and N. Misran Ionospheric and magnetic field effects observed during the 2005 geomagnetic storms in the South-East Asian sector

15:45 – 16:00 Page 168

D. Buresova, J. Lastovicka, L-A. McKinnell, T. Sindelarova, and D. Novotna A comparative analysis of mid-latitude storm-time ionospheric peak parameters variability


CHAIR LARRY PAXTON

16:30 – 16:45 Page 169

M. C. Kelley and J. Retterer New insights into prompt penetrating electric fields

16:45 – 17:00 Page 169

C. Manoj, S. Maus, and H. Lühr On the relationship between interplanetary electric fields (IEF) and equatorial-electroject (EEJ).

17:00 – 17:15 Page 170

A.H. Depueva, A.V. Mikhailov, and V.H. Depuev Morphology of quiet-time F2-layer disturbances at geomagnetic equator

17:15 – 17:30 Page 170

T. Tsugawa, K. Shiokawa, H. Hayashi, N. Nishitani, Y. Otsuka, T. Ogawa, J. Lei, and A. Saito (Invited) Large-scale traveling ionospheric disturbances observed by GPS receiver networks

17:30 – 17:45 Page 171

C. Borries, N. Jakowski, and V. Wilken Large scale TIDs observed in GPS derived differential TEC

17:45 – 18:00 Page 171

A.T. Karpachev IGW and electric field effects in the topside equatorial ionosphere

18:00 – 18:15 Page 172

I. Tsagouri, K. Koutroumbas and A. Belehaki A new ionospheric forecast model assimilating solar wind data and ground based ionosonde observations

18:15 – 18:30 Page 172

L. Scherliess, D.C. Thompson, and R.W. Schunk Specification of ionospheric dynamics at low- and mid- latitudes using a physics-based data assimilation model



Conveners D. Hysell and R. Pfaff

Time:

Author Attendance :

Full day Thursday and Friday, May 22-23

During coffee breaks, 13:00-14:00, and from 19:00 to 20:00

POSTER CHAIR MARCO MILLA AND PABLO REYES


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S9 - P4- 01 Page 174

M. Yamamoto New development of digital beacon receiver based on GNU Radio

S9 - P4- 02 Page 174

R. Pfaff, J. Kujawski, P. Uribe, K. Bromund, R. Fourre, M. Acuña, G. Le, W. Farrell, R. Holzworth, M. McCarthy, and D. Rowland The vector electric field instrument on the C/NOFS satellite

S9 - P4- 03 Page 175

J. Clemmons Paired ionosphere-thermosphere orbiters (PITO): A general-purpose science mission with high capability

S9 - P4- 04 Page 175

P. A. Bernhardt The precision expandable radar calibration sphere (PERCS) for improvement of the HF radar accuracy

S9 - P4- 05 Page 176

P. Muralikrishna A new nitric oxide detector with absorption cells driven by a fast cam system

S9 - P4- 06 Page 177

D. Kouba, J. Lastovicka, J. Boska, D. Buresova, P. Sauli, and Z. Mosna GEO-6 project and Czech participation in

S9 - P4- 07 Page 177

C. H. Lin, H. F. Tsai, C. H. Chen, J. Y. Liu, and C. H. Liu Longitudinal variation of the low-latitude ionosphere observed by FORMOSAT-3/COSMIC

S9 - P4- 08 Page 178

A. J. Gerrard and J. W. Meriwether Continual 24-hour observations of thermospheric winds and temperatures made with the Second-generation Optimized Fabry-Perot Doppler Imager (SOFDI)

S9 - P4- 9 Page 178

F. R. Galindo, K. M. Kuyeng, J. L. Chau, and D. L. Hysell Evaluation of topside equatorial spread F spectra estimators using Monte Carlo simulations

S9 - P4- 10 Page 178

A. Saito and D. Yoshida Dagik: Data-showcase system to browse multi aeronomy data in four-dimension

S9 - P4- 11 Page 179

S. Hawlitschka Observing the spatial characteristics of TIDs with broadband HF direction finding

S9 - P4- 12 Page 179

H. Haralambous, G. Dekoulis, and P. Vryonides Installation of an ionospheric station in Cyprus

S9 - P4- 13 Page 180

H. Haralambous , A. Mahrous , P Vryonides , and A. Shemis Monitoring of ionospheric weather over Cyprus and Egypt

S9 - P4- 14 Page 180

S. M. Radicella , L. Ciraolo , M. Mosert , O. Abarca , B. Zolesi , M. Pezzopane , R. Ezquer, and M. Cabrera An unusual night time ionospheric phenomenon observed at Tucumán, Argentina, under quiet geomagnetic conditions

S9 - P4- 15 Page 181

O. A. Oladipo , S. M. Radicella, and J. O. Adeniyi Comparisons between the observed electron density profile at the equatorial station of Ilorin, Nigeria, and the IRI model


ISEA-12 Program

35

S9 - P4- 16 Page 181

E. Silvestre, J. Valverde, P. Condor, O. Veliz, and C.Vallladares Total electron content over South America using LISN GPS data: 2007 climatology and special events

S9 - P4- 17 Page 182

A. B. Rabiu, K. Groves, R. S. Fayose, and O. R. Bello Ground observation of ionospheric scintillation and TEC within EEJ borders

S9 - P4- 18 Page 182

P. Høeg, X. Yin, L. Olsen, and A. Carlström Low elevation measurements of GPS ocean reflections

S9 - P4- 19 Page 183

M. Le Huy, R. Fleury, P. L. Duchesne, A. Bourdillon, C. Amory-Mazaudier, T. N. Chien, and L. Tran Thi Some results of the GPS Tec observations in the southeast Asian region

S9 - P4- 20 Page 184

O. K. Obrou, M. N. Mene, A. T. Kobea, K. Z. Zaka, B. Ouattara, and K. Groves Study of the Total Electron Content (TEC) at an equatorial station

S9 - P4- 21 Page 184

J. Valverde, E. Silvestre, and C. Valladares Inside LISN, an engineering perspective to its avant-garde conception

S9 - P4- 22 Page 185

A. B. Rabiu, K. Yumoto, I. A. Adimula, J. O. Adeniyi, and the MAGDAS/CPMN Project group Some contributions of MAGDAS to the understanding of equatorial geomagnetic field behavior

S9 - P4- 23 Page 185

A. B. Rabiu, B. J. Thompson, C. Amory-Mazaudier, M. C. Potgieter, N. Seghouani, D. Baylie, O. K. Obrou, M. C. Rabello Soares, K. Yumoto, K. Groves, U. Inan, and D. Scherrer

Africa and the International Heliophysical Year (IHY) S10 - P4- 24 Page 187

R. Pfaff, C. Liebrecht, J.-J. Berthelier, M. Parrot, and J.-P. Lebreton Irregularities at sub-auroral, middle, and low latitudes in the topside ionosphere observed during geomagnetic storms with the DEMETER and DMSP satellites

S10 - P4- 25 Page 187

H. Kil and L. J. Paxton Equatorial ionospheric disturbances during the October 29-31, 2003 storms

S10 - P4- 26 Page 188

A.V. Mikhailov, V.H. Depuev, and T.Yu. Leschinskaya Formation mechanism of quiet-time F2-layer disturbances at geomagnetic equator

S10 - P4- 27 Page 188

N. Balan, H. Alleyne, Y. Otsuka, and B. G. Fejer Relative effects of electric field and neutral wind on positive ionospheric storms

S10 - P4- 28 Page 189

J. Boska, D. Buresova, D. Kouba, and P.Šauli. E and F region midlatitude ionospheric drifts observed during geomagnetic storms.

S10 - P4- 29 Page 189

K. Schlegel, H. Lühr, M. Rother, and K. Yumoto Night-time Sudden Commencements observed with CHAMP and Ground-based Magnetometers


ISEA-12 Program

36

S10 - P4- 30 Page 190

M.M.J.L. van de Kamp and P. S. Cannon Study of ionopsheric scintillation using GPS signals measured at Ascension Island

S10 - P4- 31 Page 191

S. Sripathi, S. Bose, D. Tiwari, S. Banola, B. Kakad, A. Bhattacharyya, and T. K.Pant Response of equatorial and low latitude ionosphere in Indian region during some severe geomagnetic storms: A study


20:00 END OF DAY (Friday May 23)


ISEA-12 Program

37

SATURDAY MAY 24, 2008

SESSION S11 WHERE ARE WE GOING? OUTSTANDING QUESTIONS, FUTURE TRENDS AND CHALLENGES

Conveners M. C. Kelley and E. Kudeki

CHAIR MICHAEL KELLEY AND ERHAN KUDEKI

08:00 – 08:20 Page 192

D. C. Fritts (Invited) Atmospheric wave dynamics and their effects on the equatorial ionosphere: What do we know, what are the unknowns, and which are the important topics?

08:20 – 08:40 Page 192

J. D. Mathews (Invited) Meteor science and layering phenomena in the lower thermosphere. Is there anything that we lack in basic knowledge and how should we go about getting it?

08:40 – 09:00 Page 193

J. L. Chau et al. (Invited) What else can we learn with coherent scatter radars about E and F region irregularities that we don’t know? What else can we learn about ESF and midlatitude SF?

09:00 – 09:20 Page 193

J.-P. St-Maurice (Invited) What are the objectives/needs for new theoretical work on E and F region plasma instabilities and electrodynamics?

09:20 – 09:40 Page 195

K. Shiokawa (Invited) Optical investigation of the ionospheric and atmospheric dynamics. How can we learn something more that is significant?

09:40 – 10:00 Page 195

M. F. Larsen (Invited) Accuracy issues of the existing thermospheric wind models. Can we rely on them in seeking solutions to wind driven problems?

10:00 – 10:20 Open discussion

10:20 – 10:30 Closing remarks



11:00 END OF ISEA-12


39

ABSTRACTS


Sessions 1 & 2: Tutorials

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The equatorial E region and its plasma instabilities: A tutorial

D. T. Farley

Cornell University, Ithaca, NY, USA ([email protected])

Since this is a tutorial, we first briefly review the basic physics of the E region of the equatorial ionosphere, with emphasis on the strong electrojet current system that drives plasma instabilities that generate strong plasma waves that are easily detected by radars and rocket probes. We then discuss the instabilities themselves, both the theory and some examples of the observational data. These instabilities have now been studied for about half a century (!), beginning with the IGY, particularly at the Jicamarca Radio Observatory in Peru. The linear fluid theory of the important processes is now well understood, but there are still questions about some kinetic effects, not to mention the considerable amount of work to be done before we have a full quantitative understanding of the limiting nonlinear processes that determine the details of what we actually observe. As our observational techniques, especially the radar techniques, improve, we find some answers, but also more and more questions. One difficulty with studying natural phenomena, such as these instabilities, is that we cannot perform active cause-and-effect experiments; we are limited to the inputs and responses that nature provides. The one hope here is the steadily growing capability of numerical plasma simulations. If we can accurately simulate the relevant plasma physics, we can control the inputs and measure the responses in great detail. Unfortunately, the problem is inherently three-dimensional, and we still need more computer power than is currently available, although we have come a long way. Let us hope that Moore’s Law remains valid for at least a few more years!

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Spread F- An old equatorial aeronomy problem finally resolved?

R. F. Woodman

Radio Observatorio Jicamarca, Instituto Geofísico del Perú, Lima ([email protected])

One of the eldest scientific topics in Equatorial Aeronomy is related to Spread-F. It includes all our efforts to understand the physical mechanisms responsible for the existence of ionospheric F Region irregularities, the spread of the traces in a night-time equatorial ionogram ---which originated its name--- and all other manifestations of the same.

The phenomenon that coined its name as Spread-F, was discovered shortly after the installation of a ionosonde at the Huancayo Observatory, nearly 75 years ago. Now we know that these irregularities are also responsible for the scintillation of satellite signals and for the very strong echoes received by radars at VHF frequencies. The irregularities are observed in situ by satellite and rockets as deep fluctuations in electron density. It is our intention in this paper to review historically the advances we have made on this topic. But, considering its long history and the hundred of papers that have been written about it, we have to be very selective and concentrate only on those we (I) consider that have been landmarks in the progress we have made to understand them.

The progress was very slow at the beginning. Thirty five yeas after its discovery, although quite a bit had been learned about its geographical and temporal behaviour, Jicamarca radar observations showed that none of the theories that had been put forward could explain all of the observations. Gravity, vertical winds and electric fields had been proposed as the source of energy for unstable mechanisms that, given a density gradient, would develop electron density fluctuations (irregularities). The problem was that irregularities were also observed by Jicamarca when-and-where these conditions where stabilizing instead.



42

This apparent paradox was resolved a few years later, again by Jicamarca observations. This time the radar could see the morphology of the irregularities in the context of the background ionosphere thanks to a newly developed imaging technique. Four different types of irregularities were identified: topside, bottom-side, bottom-type and valley-type. Irregularities were observed at the top side of the ionosphere, and although this was an altitude that was gravitationally stable, the images show that they were physically connected with the lower, gravitationally (Raleigh-Taylor) unstable region. It was clear that the bottom unstable region had been convected by buoyancy to the stable region, carrying with it the conditions (low densities) that made it unstable in the first place. Numerical simulations proved that Raleigh-Taylor instabilities would indeed propagate, in a non-linear regime, to the stable top side of the ionosphere. Later, the role of gravity, electric fields and winds was unified into a single theory: the destabilizing force produced by gravity was complemented (or reduced) by forces produced by neutral friction induced by an electric field or a neutral wind (Generalized Raleigh-Taylor instability).

A problem remained, the growth time of the Raleigh-Taylor or the Generalized instability was much too long to explain the observed relatively short time available for its growth. Gravity waves were postulated as a means of producing sufficiently large fluctuations (seeding) to start with, so that the instability would not require a long time to produce a sufficiently large amplification factor. Much effort has been made in the last few decades to prove, without much success, that this is the case. A very recent theory claims that the very large counter streaming velocities, of the order of 200 m/s, between the ionized and the neutral gas, existent at the bottom of the F region during the evening hours, makes the steep gradient in electron density at this altitude (interchange) unstable. The growth time of this instability is very fast. In an hour grows 18 e-folds. When conditions are right, these resultant larger fluctuations produce the necessary seeding for the Rayleigh-Taylor instability to take over, producing the bottom-side type of Spread F or even the plumes that characterize the top side irregularities. If the conditions are not right, the irregularities remain in the unstable, but narrow, steep gradient region, and produce the (almost) ever present bottom-type traces seen by the radar. With this theory, the role and variation of the neutral winds from day to day may help us to understand the day to day variability of the phenomenon, and help us improve its predictability. The latter is much needed for practical applications.

An important experimental advance has been the development of within-the-beam interferometric imaging technique. It allows us to discriminate spatial from temporal variations and see smaller scale irregularities than it was possible with the single-beam time-scanning technique.

Little theoretical effort has been made to explain the valley-type irregularities, but the same mechanism postulated for the seeding above could work on the steep gradients present in this region, particularly when the large pre-reversal electric fields are included. Both of these latter irregularity types are not capable of producing satellite scintillations or spread in the ionogram traces.

One problem would still remain. How are the 3 m and 0.35 m irregularities responsible for the radar echoes produced? This is important since we use them as a tracer to tell us what is happening at the larger scales. Unified interchange instability numerical models using fluid equations show growth at meter scales. But, how valid are the fluid equations used at these length scales? We need non-homogeneous kinetic descriptions to validate the results. This work is still to be done.

________________________________

Atmospheric waves and wave coupling

R. A. Vincent

Deparftment of Physics, University of Adelaide, Adelaide, SA 5005, Australia ([email protected])



43

Atmospheric waves have periods ranging from a few minutes to tens of days. This talk will focus on atmospheric gravity (buoyancy) waves, tides and large-scale planetary waves. These waves play important roles in the middle and upper atmosphere because they efficiently couple energy and momentum from their source regions to regions where they dissipate. The resulting body forces drive large-scale circulations that profoundly affect the state of the atmosphere.

The theory of wave-mean flow interactions will be outlined and the importance of waves and wave effects in equatorial regions discussed. Phenomena such as the quasi-biennial oscillation (QBO) and the semiannual oscillations at the stratopause and mesopause are primarily wave driven, although the relative importance of different wave types has yet to be established. Transient wave events, such as the quasi-2-day wave and 5-7 day wave, also appear to play important roles in changing the state of the equatorial MLT.

________________________________

Mid-latitude electrodynamics and plasma physics: A tutorial

M. C. Kelley

Cornell University, Ithaca, NY, USA ([email protected])

After an initial decade or two, during which the Arecibo Observatory made enormous progress in ionospheric electrodynamics, something of a lull occurred as interest migrated to the equatorial and auroral zones. But with the advent of all-sky airglow imagers and imaging coherent scatter radars, some of the complexities of mid-latitude phenomena have been clarified. In this tutorial we will review the current state of the art in mid-latitude electrodynamics and plasma physics.

________________________________

Internal and external influences on ionospheric electrodynamics at low and middle latitudes

R. A. Heelis

University of Texas at Dallas, USA ([email protected])

In the presence of the Earth’s magnetic field, the distribution of charged and neutral particles with altitude produces an anisotropic electrical conductivity. At low and middle latitudes the electron mobility parallel to the magnetic field is sufficiently high to allow electric potentials to map almost unattenuated in this direction. Perpendicular to the magnetic field the conductivity is distributed in two layers at altitudes identified with the E region and the F region ionosphere. In the lower layer, a large Hall conductivity supports intense currents known as electrojets that can be further enhanced by the orientation of the magnetic field. The distribution of Pedersen conductivity in both layers provides the opportunity for current loops to connect the E- and F-region through field-aligned currents. In a quasi-steady state electric potentials are then distributed to insure that the total current is divergence free everywhere.

Electric fields at low and middle latitudes are produced by externally applied potentials at high latitudes and by internally generated potentials resulting from neutral wind driven currents. To understand these electric field sources it is of course necessary to describe the quiet and disturbed time behavior of the neutral winds. However, it is also necessary to appreciate how applied potentials are dependent on the behavior of the conductivity integrated along the direction of the magnetic field, and on conditions in the solar wind and the magnetosphere.



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During quiet times the actions of migrating and non-migrating tides in the E region can be identified in drift patterns that have diurnal and semi-diurnal variations. The influence of meridional and zonal winds in the F-region may also be identified by expected longitudinal variations. The influences of the variations in the solar wind and the magnetosphere are most readily seen during storm times but may also be identified during moderately quiet times. These influences are associated with expansion of the area influenced by these inputs, by modification of the neutral winds by energy inputs and by penetration of electric fields inside the plasmasphere. In this work we will first describe the underlying physical principles that govern the behavior of electric fields at low and middle latitudes. Then, observational and computational results will be utilized illustrate these principles at work during quiet and disturbed times.

________________________________

Lower and middle atmospheric electrodynamics

U. S. Inan

Stanford University, Stanford, California, USA ([email protected])

Electrodynamics of the upper and middle atmosphere is significantly affected by dynamic phenomena in the lower atmosphere, in particular driven by thunderstorm and lightning activity. Precious little is known about the dynamics and chemistry of the altitude range below ~60 km, especially at night, due to the extremely low densities, that preclude any useful radar measurements. Transient disturbances produced by individual lightning discharges, as well as longer lasting effects (e.g., ionization enhancements or elevated electron temperatures) maintained through the duration of intense thunderstorms present windows-of-measurability that may help us better understand the highly complex dynamics of these regions. The measurables become available during brief periods of spectacular optical displays, known as sprites, gigantic blue-jets, elves, as well as in the form of ionization/temperature enhancements, and Terrestrial Gamma-ray Flashes (TGFs). Chemical response of the middle atmosphere to these dynamic disturbances is clearly measurable, and allows the assessment of the rate coefficients of different processes (e.g., attachment, recombination). For example, during clearly measurable ionospheric signatures of lightning-induced electron precipitation events, the energies of the radiation belt electrons involved can be as high as several Me, in which case the disturbances produced are at altitudes as low as ~50-60 km. In recent years, several examples of unusually long lasting (tens of minutes instead of tens of seconds) disturbances have been observed, which defy the predictions of currently available chemistry models.

The electrodynamics of the middle atmospheric phenomena driven by lightning discharges can be highly complex, requiring dynamic solutions of the Boltzmann’s equation together with Maxwell’s Equations, with the myriad of the elastic and inelastic loss processes in air accounted for. The resulting optical, x-ray, and ionization enhancement (or attachment driven depletion) responses are thus equally complex and rich, but thus present the opportunity of extracting heretofore-unavailable information about the many underlying complex processes. Part of the complexity of the responses result from the variability of the driving fields (EMP and quasi-static) that are released in lightning discharges. However, a substantial part of the observed complexity is a result of the highly variable ambient density and conductivity profiles of the night-time lower ionosphere. In this talk, we review the basic electrodynamics of the lower and middle atmosphere, with particular attention to dynamic response of the system to intense fields and sudden disturbances.


Session 3: Equatorial Lower- and Middle- Atmosphere Studies

45

Dynamics of the QBO and SAO revealed by a gravity-wave resolving GCM simulation

K. Sato1, Y. Kawatani2, S. Watanabe2, Y. Tomikawa3, S. Miyahara4 and M. Takahashi1,5

1: Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan 2: Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan ([email protected]) 3: National Institute of Polar Research, Tokyo, Japan 4: Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Fukuoka, Japan 5: Center for Climate System Research, University of Tokyo, Kashiwa, Japan

A high-resolution atmospheric general circulation model (AGCM) has been developed to study various aspects of small-scale phenomena including gravity waves and their role on the large-scale fields in the middle atmosphere (Watanabe et al. 2008). Our spectral model has a T213 truncation in the horizontal (horizontal resolution of about 60 km) and 256 layers (L256) in the vertical from the surface to about 85 km with an interval of 300 m in the upper troposphere and above. No gravity wave parameterizations are included in our model and hence all gravity waves are spontaneously generated. The model simulates large-scale oscillations with realistic amplitudes in the equatorial atmosphere such as the quasi-biennial oscillation (QBO) and semi-annual oscillation (SAO), although the period of the QBO-like oscillation is shorter (about 1.5 years) than the real one.

Model outputs with a time interval of 1 hour are analyzed to elucidate relative importance of the internal gravity waves (IGWs) and equatorially-trapped waves (EQWs) to drive the QBO-like oscillation. It is shown that the zonal wavenumber versus frequency spectra of simulated precipitation and outgoing long wave radiation (OLR) represent realistic signals of convectively-coupled EQWs. The horizontal wind spectra reveals clear signals of equatorial Kelvin waves, Rossby-gravity waves, and n=0 eastward, n=1 and n=2 eastward/westward propagating gravity waves in the stratosphere. These wave signals are separately extracted for further examination following Wheeler and Kiladis (1999). The horizontal distribution of each EQW amplitude generally corresponds well to that of the activity of cumulus convection. On the other hand, it is seen that IGWs are strongly influenced by the vertical wind shear associated with the Walker circulation in the troposphere, which results in different distribution of IGW amplitudes between the eastern and western hemisphere. In the westerly shear phase of the QBO-like oscillation, IGWs contribute to 50-70% of the total eastward acceleration. The equatorial Kelvin waves contribute to the largest forcing among EQWs especially around the altitude with a zonal wind of 0 m/s, while the forcing due to n=0, 1, 2 eastward-propagating EQWs becomes comparable to that of Kelvin waves at higher altitudes. It is interesting that the distribution of the wave forcing is not zonally uniform and is different depending on the wave types.

The simulated SAO has larger amplitudes of the zonal-mean zonal wind in the first cycle than in the second cycle. The easterly and westerly maxima are about -70 (m/s) and 35 (m/s) for the first cycle, respectively, while those are about -50 (m/s) and 35 (m/s) for the second cycle. Fast Kelvin waves are obvious in the easterly phase of the SAO, probably because slow Kelvin waves are effectively filtered by the QBO westerly below. The candidates of driving mechanism of the SAO are the momentum deposition by internal waves with large phase velocities and the momentum transport by the meridional circulation. Tomikawa et al. (2008) focused on a temperature maximum observed in the winter subtropical region around the stratopause and showed the importance of the meridional circulation appearing in the easterly wind of the SAO, using the same model outputs. It is likely that this meridional circulation is driven by the



46

E-P flux convergence associated with planetary waves. This circulation may be important to maintain the SAO easterly phase.

________________________________

Tropical GPS atmosphere turbulence

P. Høeg1, L. Olsen1, and A. Carlström2

1: Aalborg University, Aalborg, Denmark ([email protected]) 2: Saab Space, Gothenburg, Sweden

High altitude field tests have established experimental knowledge on the influence of atmosphere turbulence on GPS receiver performance in tropical regions. Moist air turbulence measurements from Haleakala, Hawaii, are studied for spectral signal structure characteristics. The performed spectral properties of the received signals by a high precision dual-frequency GPS instrument in both phase-locked mode (PL) and open-loop mode (OL) are compared to simulated results.

The OL mode provides sampling rates up to 1000 Hz, which enables investigation of spectral signatures that are normally not seen in GPS data. The use of directive antennas pointed towards the horizon give signal recordings down to the lowest layers of the atmosphere. We have analyzed the signal dynamics and spectral content of low-elevation measurements in OL tracking mode. We find that the high-frequency part of the signal is dominated by thermal noise, while the lower frequency part is dominated by clock-noise, which for the receiver rubidium clock falls off as the inverse of the frequency squared. In order to study atmospheric low-elevation turbulence by spectral analysis, we investigated spectral fluctuations above the noise characteristics of the clock caused by the turbulent atmosphere.

The main atmospheric modulation of GPS signals in low-elevation measurements is attenuation and frequency shift due to ray bending, whereas the presence of turbulence is causing a spectral broadening of the signal. Displaying the power spectrum as function of frequency difference from the main signal peak reveals the characteristic domains of the spectrum. Up to 10 Hz, the spectrum is approximately sloping as the inverse of the frequency squared. While for higher frequencies, in the range 10 - 500 Hz, the spectrum flattens. The latter part of the spectrum originates from thermal noise, while the first sloping part is characteristic for the rubidium frequency reference used in both the GPS transmitter and the receiver. Analysis of the trend of the mean slope in the spectra for different frequency domains showed an increased slope as function of the elevation of the received signal above the horizon, indicating turbulence and eddies in the beam direction. Analysis of the trends of the mean slope in the spectra for different frequency domains will be discussed in relation to the characteristics of turbulence.

The OL data sampling rate of 1000 Hz enables detection and investigation of the characteristics of the noise and the multi-path signal error sources through the determination of the refractive index structure constant Cn

2 of the atmosphere turbulence. Based on knowledge of the geometry of the experiment and models for the turbulence, it has been possible to determine scale sizes and structure constant changes from the measured spectral variances.

________________________________

MST radar observation – capacity and limit

Susumu Kato

Kyoto University, Japan ([email protected])



47

MST (Mesosphere, Stratosphere, Troposphere) radar observation isuseful for the study of MST dynamics. The radar tracks radio refractive –index (RRI) perturbation produced by atmospheric turbulence moving with local winds. It has been known, since the 1980s, that gravity wave (GW) breaking is responsible for the production of turbulence taking place at any height. The principle of MST radar observation of winds is based on measurementof the radar-pulse Doppler-shift caused by local winds carrying RRI perturbation which is produced by turbulence. Observationally, the validity of the measurement has been checked. However, we are not yet certain as to how the refractive index perturbation is produced by turbulence. Different from the conventional understanding we propose an understanding in which the existence of static vertical gradient of RRI is essential for RRI to be perturbed by turbulence and co-move with turbulence. This is true even in the mesosphere where electromagnetic forces affect the perturbation. We are ignorant as to whether the established theory of isotropic turbulence can be valid for the real atmospheric turbulence which is possibly anisotropic in the presence of gravity force. Note that tropospheric radio-sonde observation (Lovejoy et al. GRL., 2007) is suggesting that atmospheric turbulence is really anisotropic.

________________________________

MU radar 1D, 2D, and 3D imaging of atmosphere and ionosphere

M. Yamamoto1, G. Hassenpflug2, S. Saito2, H. Luce3, S. Fukao4

1: Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Kyoto, Japan ([email protected]) 2: National Institute for Information and Communications Technology (NICT), Tokyo, Japan 3: LSEET-LEPI, Toulon-Var South University, Toulon, France 4: Research Institute of Science and Technology, Tokai University, Tokyo, Japan

Radar imaging is a new technique for atmospheric and ionospheric radars. Resolution of the radars is very much enhanced by the imaging analysis with multiple-antenna and/or multiple-frequency observations. In addition to the flexible multi-beam capability of the MU radar, that is the original advantage of the system, the radar is now equipped with “MU radar imaging observation system” since March 2004: It consists of ultra multi-channel digital receiving subsystem that digitally demodulate 5 MHz IF signals at 29 channels (25 channels for all sub-groups of antenna, and 4 channels corresponding to analog signal-combiners). In addition to the digital receivers, we widened the radio-band allocation to 3.5MHz. We can now shift the radar frequency to at most five different frequencies at each pulse. This paper overviews recent results of our study utilizing the new feature of the MU radar. One most successful application is the study of thin-layered structure of the atmosphere with “1D imaging” in the frequency domain (Frequency radar Interferometric Imaging (FII) technique). Cumulus convection and Kelvin-Helmholtz instabilities (KHI) are clearly elucidated from observations with Capon method analysis (Luce et al, 2007). “2D imaging” in the spatial domain is very successful to investigate structures of ionospheric irregularities. The maximum entropy analysis with 19-channel signals (i.e., use all hexagonal sub-groups) is the standard observation mode (Saito et al., 2007). We can conduct the imaging observations at multiple-beam directions as well. We are now developing a “3D imaging” technique for the study of lower atmosphere. As it combines multi-channel and multi-frequency observations of at most 19-channel X 5-frequency, signal processing load is very heavy. From our study we will show an example of the KHI observed by the 3D imaging (Hassenpflug, et al., 2008).



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References

Luce, H., G. Hassenpflug, M. Yamamoto, M. Crochet, and S. Fukao, Range-imaging observations of cumulus convection and Kelvin-Helmholtz instabilities with the MU radar, Radio Sci., 42, RS1005, 2007.

Hassenpflug, G., M. Yamamoto, H. Luce, and S. Fukao, Description of demonstration of the new Middle and Upper atmosphere Radar imaging system: 1-D, 2-D and 3-D imaging of troposphere and stratosphere, Radio Sci., in press, 2008.

Saito, S., M. Yamamoto, H. Hashiguchi, A. Maegawa, and A. Saito, Observational evidence of coupling between quasi-periodic echoes and medium scale traveling ionospheric disturbances, Ann. Geophys., 25, 2185-2194, 2007.

________________________________

Variability of mesospheric diurnal tides and tropospheric diurnal heating during 1997-1998

R. S. Lieberman1, D. M. Riggin1, D. A. Ortland2, S. W. Nesbitt3 and R. A. Vincent4

1: Northwest Reserach Associates, Colorado Research Associates Division ([email protected] ) 2: Northwest Reserach Associates, Seattle, Washington 3: University of Illinois 4: University of Adelaide

This study focuses on interannual variations of diurnal tropospheric heating, and the response in the mesosphere observed by radars and predicted by a model. The work is prompted by the possible connection between low-latitude tidal variability during 1997-98, and the El Nino-Southern Oscillation. Water vapor absorption of solar radiation, and latent heat release due to deep convection both exhibit anomalously higher amplitudes in the tropical central and eastern Pacific during 1997--98: The altered water vapor heating forces stronger migrating diurnal tides, while the latent heating pattern generates several nonmigrating modes. A primitive equation model is used to evaluate how these sources contribute to diurnal winds in the mesosphere. The timing of the model amplitude enhancements is consistent with observations at Hawaii, although the observed increases are significantly stronger. Our study indicates that water vapor heating is the larger contributor to tidal enhancement observed during 1997-98.

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New Results in Mesospheric Aeronomy Studies: a Review

J. Meriwether

Clemson University, Clemson, SC ([email protected])

Recent highlights from the aeronomy of the mesosphere and lower thermosphere regions illustrate the range of interesting phenomena that exist at the edge of space. A particular example is the mesosphere inversion layer that has been observed since 1976 and still, its origin remains not particularly well understood. Another example is the development of atmospheric instability layers that contribute to the formation of turbulent structures. A third is the interaction of gravity waves with tidal waves that support the development of tidal bores and wave ducting. Rayleigh and resonance lidar measurements have provided key measurements that have contributed to the progress made in understanding these phenomena. Of equal importance have been the results from TMA chemical release measurements that have revealed the persistence of high speed winds in the 110 to 120 km region that cannot be explained by tidal or gravity wave activity.



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Twin Mesospheric Bores

A. F. Medeiros1, M. J. Taylor2, J. Fechine1, H. Takahashi3, R. A. Buriti1 and L. M. Lima4

1: Universidade Federal de Campina Grande, Campina Grande, PB, Brazil 2: Center for Atmospheric and Space Sciences, Utah State University, Logan, UT, USA 3:Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP, Brazil 4: Universidade Estadual da Paraiba, Campina Grande, PB, Brazil

Coordinated observations were made from northeastern Brazil using two all-sky CCD cameras, one located at São João do Cariri (7°S, 36°W) and operated by the Federal University of Campina Grande. The second camera, from Utah State University, was located at Monteiro (7.9°S, 37.1°W) giving a site separation of ~85 km. On the night December 19 2006, two consecutive bore events were observed in the OH and OI5577 emissions separated by ~3 hours both exhibiting similar properties and propagating due eastward. However, the first event exhibited a dark leading front with several trailing waves progressing into a brighter airglow region. In contrast, the second bore comprised several bright waves propagating into a darker airglow region. In this paper we show the first time one case of the Twin Mesospheric Bores.

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Magnetized Rossby waves as a possible driver for the lower E region neutral wind maximum

M. F. Larsen

Clemson University, Clemson, South Carolina, USA ([email protected])

Observations of neutral winds in the lower E region have consistently shown large wind speeds that significantly exceed predictions based on established theory, such as tidal theory. The wind speed maxima, which are typically found in the altitude range between 95 and 115-km altitude, were first observed with chemical release measurements from sounding rockets, but have more recently been identified in radar, lidar, and satellite data. Observations from satellites are limited but suggest that the winds extend over broad ranges of latitude and longitude and are not localized chaotic features or short-period wave structures. The mechanism that drives the enhanced winds is still unknown, but a mechanism for accelerating the neutral winds in the lower E region will be presented here. Several recent papers have presented theories for magnetized Rossby waves (MWR), which represent waves with features similar to neutral Rossby waves modified by the effects of the Hall conductivity. A critical characteristic of the MWR’s in this context is that their dynamics are associated with a reverse cascade that leads to an acceleration of the large-scale winds. The altitude range where the Hall conductivity drag terms are important also represents the altitude range where MWR’s are expected to be important. An overview of the observed wind characteristics will be presented. The expected characteristics of the MWR’s will also be described, including the expected wavelengths, wave periods, and spatial distribution. Finally, the time constants for wave acceleration of the large-scale flow will be discussed, as well as the extent to which MWR’s can account for the observed wind characteristics.



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First results from the São José dos Campos temperature LIDAR

D. Simonich and B. Clemesha

Instituto Nacional de Pesquisas Espaciais ([email protected])

In 2006 we started to integrate a new laser into our LIDAR. It uses a 1064 nm Nd:YAG seeded oscillator mixed with a 1319 nm Nd:YAG laser consisting of a seeded oscillator, pre-amplifier and a 2 stage amplifier to generate narrow band (~0.2 pm) 589 nm output. Thermal tuning of the 1064 nm seeder is used to change the wavelength in order to make temperature measurements. During 2007 we had 83 nights with both density and temperature data. The most interesting night was 20070824 which had a large localized temperature peak at 2428 hrs. Based on 5 point running means (height and time) the peak value of temperature was 435 º K at 85.18 km. The temperature pulse lasted about 20 min. Just after the temperature spike ends a density increase starts very near the peak height of the temperature maximum at 86.67 km and increases in density until 2506 during which time there was a temperature increase from 220 to 240 º K which coincided with the peak density at this time. This may have been a long-lived meteor trail. A somewhat similar event occurred on 20071011 at 2339 hrs and 96.5 km with a temperature rise from a background of around 190 º K to 265 º K in approximately 5 min, decaying back to a background of about 200 º K in about the same time. Approximately 20 min later there was a sporadic sodium layer at essentially the same height with a strength factor of 7 and a peak density of 21.5 x10-9 m-3: Several nights showed descending temperature isopleths associated with rapid density changes later in the night when the descending isopleths went below 90 km. There were a few instances of sporadic sodium layers which appear to be associated with temperature changes. On 20070730 at about 2330, for example, a strong sporadic layer at 96 km was associated with a temperature increase of about 40 º K. On the other hand there are cases where substantial temperature changes appear to be unrelated to density. Near the beginning of the data on the night of 20070815 there were three sporadic layers above the principal layer in the region of 97 to 108 km. At 1928 hrs these layers were above 100 km, with strength factors of 4.3, 2.2 and 3.5: There was no correlation with temperature variations for this region.

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Zonal structure in the equatorial ionosphere: both sides of the GPS radio occultation story

K. Cahoy

Stanford University, Stanford, CA, USA ([email protected])

Atmospheric thermal tides appear to have significant interaction with the E and F regions of the equatorial ionosphere, based on results from the NASA TIMED-GUVI and IMAGE-FUV instruments [e.g., Sagawa et al., 2005; Immel et al., 2006; England et al., 2006], electron density from FORMOSAT-3/COSMIC GPS radio occultation measurements [Lin et al., 2007], GSWM and TIME-GCM simulations [Hagan et al., 2007], and magnetometer measurements of the EEJ [Alken et al., 2007]. In particular, TIME-GCM results indicate that the zonal wave-4 structure observed by the UV imagers near the spring equinox of 2002 is consistent with the structure of an eastward-propagating zonal wavenumber 3 diurnal tide (DE3) that is excited by latent heat release associated with raindrop formation in the tropical troposphere [Hagan et al., 2007].

GPS radio occultation profiles not only yield profiles of electron density in the ionosphere, but also profiles of refractivity in the neutral atmosphere, from which temperature and pressure are derived



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[Kursinski et al., 1997]. Examination of both the top and bottom sides of the GPS radio occultation profiles provides additional information about concurrent variability in the tropical troposphere and upper atmosphere. In this work, week-long subsets of electron density, refractivity, and temperature/pressure profiles from FORMOSAT-3/COSMIC around the equinoxes and solstices of 2007 are examined for nonmigrating tidal structure and variability both during the daytime and at night. The publicly available1 FORMOSAT-3/COSMIC electron density profiles extend from about 100—450 km altitude. The refractivity and temperature/pressure profiles extend from near-surface to about 60 km altitude, leaving a roughly 40 km gap between the data sets. Analyses of both neutral and electron density structures, similar to the approach in [Cahoy et al., 2006] for Mars, will be presented for each of the equinoctial and solstitial data subsets.

References:

Alken P., S. Maus (2007), Spatio-temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC-C satellite magnetic measurements, J. Geophys. Res., 112, A09305, doi:10.1029/2007JA012524

Cahoy K. L., D. P. Hinson, G. L. Tyler (2006), Radio science measurements of atmospheric refractivity with Mars Global Surveyor, J. Geophys. Res., 111, E05003, doi:10.1029/2005JE002634

England, S. L., T. J. Immel, E. Sagawa, S. B. Henderson, M. E. Hagan, S. B. Mende, H. U. Frey, C. M. Swenson, and L. J. Paxton, (2006) Effect of atmospheric tides on the morphology of the quiet time, post-sunset equatorial ionospheric anomaly, J. Geophys. Res., 111, A10S19, doi:10.1029/ 2006JA011795

Hagan M. E., A. Maute, R. G. Roble, A. D. Richmond, T. J. Immel, S. L. England (2007), Connections between deep tropical clouds and the Earth's ionosphere, Geophys. Res. Lett., 34, L20109, doi:10.1029/ 2007GL030142

Immel, T. J., E. Sagawa, S. L. England, S. B. Henderson, M. E. Hagan, S. B. Mende, H. U. Frey, C. M. Swenson, and L. J. Paxton, (2006) The control of the equatorial ionospheric morphology by atmospheric tides, Geophys. Res. Lett., 33, L15, 108, doi:10.1029/2006GL026161

Kursinski, E., G. Hajj, J. Schofield, R. Linfield, and K. Hardy (1997), Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System, J. Geophys. Res., 102(D19), 23429-23465

Lin C. H., W. Wang, M. E. Hagan, C. C. Hsiao, T. J. Immel, M. L. Hsu, J. Y. Liu, L. J. Paxton, T. W. Fang, C. H. Liu (2007), Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3/COSMIC: Three-dimensional electron density structures, Geophys. Res. Lett., 34, L11112, doi:10.1029/ 2007GL029265

Sagawa, E., T. J. Immel, H. U. Frey, and S. B. Mende, (2005), Longitudinal structure of the equatorial anomaly in the nighttime ionoshere observed by IMAGE/FUV, J. Geophys. Res., 110, doi:10.1029/2004JA010848

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Wave-4 structure in the thermospheric zonal wind at dip equator latitudes as observed by CHAMP

K. Häusler, and H. Lühr

GeoForschungsZentrum Potsdam, Potsdam, Germany ([email protected])

The accelerometer onboard CHAMP located at the center of gravity enables us to derive the thermospheric zonal wind at orbit altitudes (~400km). Examining the longitudinal dependence of the zonal delta wind (deviations from the zonal average), a dominance of the wavenumber 4 in the Equinox data could be revealed. The wave-4 pattern is a prevailing feature in the slowly precessing satellite frame. In the Mesosphere Lower Thermosphere (MLT) region the basic wave responsible for the wave-4 pattern is 1 The author would like to gratefully acknowledge of the volumes of data maintained and provided by UCAR’s Cosmic Data Analysis and Archival Center (CDAAC).



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said to be the eastward propagating diurnal tide with zonal wavenumber 3 (DE3). This wave is primarily excited by latent heat release in the tropical troposphere. How the wave-4 structure is coupled to the upper thermospheric zonal wind is still not completely clarified. However, Oberheide and Forbes (2008) report that a significant part of the observed wave-4 structure in the zonal wind can be attributed to direct tidal upward propagation. The purpose of this paper is to identify the annual variation of the wave-4 longitudinal structure in the zonal delta wind along the dip equator using four years of data. Therefore, monthly means of local time distributions of the wave-4 pattern in the zonal wind are determined. The results are compared with the annual variation of the DE3 signature in other parameters and from other heights in order to obtain deeper inside in the vertical coupling.

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Radar cross-sections for mesospheric echoes at Jicamarca: Measurements and estimates from turbulence theory

G. Lehmacher1, E. Kudeki2, A. Akgiray2, and Jorge Chau3

1: Clemson University, Clemson, South Carolina, USA (glehmac@clemson,.edu) 2: University of Illinois at Urbana-Champaign, Illinois, USA 3: Radio Observatorio Jicamarca, Lima, Peru

Based on the MST-ISR mode at the 50-MHz Jicamarca main radar, Akgiray (2007) developed an algorithm to calculate calibrated backscatter radar cross-sections (RCS) for mesospheric echoes. As expected, RCS values are highly variable with time and altitude; typical values range from 10-18 to 10-15 m-1 These RCS are caused by various and still poorly understood scattering processes from electron density irregularities at the Bragg scale (3 m). Some layers show clear evidence of Kelvin-Helmholtz instabilities, which produce isotropic and anisotropic turbulence structures, and which have been studied in high-resolution numerical simulations. We compare predictions for RCS, based on classical 3-dimensional turbulence, with the measured RCS. Here, a large number of important parameters must be guessed. Turbulent energy dissipation rates and Richardson numbers are being estimated from the measured radar spectra, while background temperature and electron density must be taken from models. We will also include results from rocket measurements in the equatorial D region, which often show steep temperature and electron density gradients, thereby considerably increasing the range of predicted RCS values.

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In-situ evidence of nighttime midlatitude plasma density perturbations produced by gravity waves

G. D. Earle1, A. M. Musumba1, and S. L. Vadas2

1: William B. Hanson Center for Space Sciences, The University of Texas at Dallas, USA ([email protected]) 2: NorthWest Research Associates, CoRA Division, Boulder, CO, USA

Late in its life the perigee of the Dynamics Explorer-2 (DE-2) satellite was sufficiently low to sample the bottomside of the nighttime F region ionosphere. During several of these excursions the Duct-Sensor instrument measured ~30% fluctuations in the plasma density associated with meso-scale nighttime wave structures at magnetic midlatitudes. On some of these orbits the DE-2 observations included simultaneous measurements of ion drifts from the IDM instrument and neutral density and winds from the NACS and WATS instruments, respectively. These measurements consistently show anti-correlations between the



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plasma and neutral density fluctuations, and closely related ion and neutral vertical velocities. The intrinsic wave period inferred from the measurements is about 30 minutes, which is consistent with gravity wave propagation at these altitudes. The measurements are in excellent agreement with the predictions of a numerical model based on a more complete gravity-wave dispersion relation that includes both thermal diffusion and kinematic viscosity effects. Both the predicted dissipation heights and the horizontal wavelengths predicted by the model agree with the observations, suggesting that meso-scale structuring due to gravity wave induced-transport and attendant recombination chemistry may be common below ~300 km at midlatitudes.

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Combined impedance probe and Langmuir probe studies of the low-latitude E region

D. E. Rowland1, R. F. Pfaff2, and C. T. Steigies3

1: NASA Goddard Space Flight Center, Greenbelt, MD ([email protected]) 2: Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany

The EQUIS-2 sounding rocket and radar campaign, launched from Kwajalein Atoll in 2004, included a mission to study low-latitude irregularities and electrodynamics, led by NASA GSFC. This mission included two instrumented rockets launched into the nighttime E region (apogee near 120 km), which included comprehensive electrodynamics and neutral density instrumentation. These rockets carried the first of a new generation of impedance probes, that utilize a wide-band drive signal to simultaneously measure the impedance of an antenna in a plasma as a function of frequency from 7 kHz to 4 MHz, at a rapid cadence. This technique promises to permit true plasma spectroscopy, and resulted in the identification of multiple plasma resonances and accurate measurements of the plasma density, even in the low density nighttime E region.

We present analyses of the technique and resulting spectra, and show how these data may be combined with fixed-bias Langmuir Probe data to infer the temperature structure of the E region as well as providing accurate absolute calibrations for the very high time resolution fixed-bias probe data. The data is shown to agree well with data from ionosonde, the ALTAIR radar, and the Peruvian beacon experiment.


Session 4: Equatorial and mid-latitude MLT dynamics

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Gravity wave distribution at low and mid-latitudes from the Nested Regional Climate Model

Han-Li Liu, Jimy Dudhia, and Bill Kuo

National Center for Atmospheric Research ( [email protected] )

Gravity waves are generated from the orography, convection, and spontaneous adjustment of unbalanced jet flow, with spatial scales from 10-1000 km and temporal scales between buoyancy frequency and intertial frequency. The gravity waves can significantly impact the energy and momentum budget, the transport and mixing of atmospheric species, and stability and variability in the middle and upper atmosphere. The vastly different spatial and temporal scales and the global distribution of the gravity waves pose a stiff change for both observational and numerical studies of the gravity waves. In recent years, very high resolution numerical simulations can be afforded with the increasing computational power, and gravity waves at increasingly finer scales can be resolved in regional and even global domains. In this study, results from the Nested Regional Climate Model (NRCM) are examined. The NRCM has a global coverage between 45S and 45N (thus a channel model) with horizontal resolution of 36 km, and extends from the ground to ~30 km. The potential energy density of the gravity wave perturbations between 100-1000km from the model is compared with that obtained from GPS measurements. Analyses of gravity wave characteristics, energy and momentum flux, their distribution at low and mid-latitudes, and their seasonal variation in the upper troposphere and lower stratosphere will be presented.

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Seasonal variations in gravity wave activity at three locations in Brazil

B. R. Clemesha and P. P. Batista

Instituto Nacional de Pesquisas Espaciais, São José dos Campos, SP, Brazil ([email protected])

Using the variance in meteor radar winds as a measure of gravity wave intensity, we investigate the temporal variations in gravity wave activity at three locations in Brazil: São João do Cariri (7.3 S, 36.4 W), Cachoeira Paulista (22.7 S, 45.0 W) and Santa Maria (29.7 S, 53.7 W). The technique used is that of Hocking (2005) which makes it possible to separate the zonal and meridional components of the fluctuating wind velocity. We find that the seasonal variation of the fluctuating wind is similar to that of the amplitude of the diurnal tide, showing a predominantly semi-annual variation, stronger at Cachoeira Paulista and Santa Mara than at the quasi-equatorial station, Cariri. Both with respect to the seasonal trend and shorter term variations, strong coupling between gravity wave activity and tides is indicated by a remarkably close correlation between the fluctuating velocity and the vertical shear in the tidal winds. This coupling suggests that tidal wind shear might be an important in situ source of gravity waves in the mesopause region.



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Seasonal and interannual variability of gravity waves at Adelaide and Alice Springs

L.J. Gelinas 1, J.H. Hecht 1, R. Walterscheid 1, and R.G. Roble2

1: The Aerospace Corporation, El Segundo, CA USA ([email protected]) 2: National Center for Atmospheric Research, Boulder, CO USA

The mesosphere and lower thermosphere (MALT) is a region largely controlled by tides and gravity waves. In this paper, we explore the seasonal and interannual variability of the MALT and its relationship to gravity wave fluxes using long-term airglow measurements at two Australian sites. The data presented here are the result of more than five years of airglow imager observations at Adelaide 34°55’S, 138°36’ E) and Alice Springs (23°42’ S, 133°53’ E). The imagers measure rotational temperature and intensity of two atmospheric emissions, OH Meinel (6, 2) and O2 atmospheric (0, 1). The use of imagers, rather than photometers, also provides information about shorter-period gravity waves, an important driver of seasonal variability. Climatological analysis of emission temperatures and intensities at Adelaide and Alice Springs, including comparison to the NCAR TIME-GCM, was recently completed (Gelinas et al., 2008). It was shown that the model successfully reproduces many observed features of the data: the equinoctial maxima associated with the diurnal tide, a 6-hour phase shift between OH temperature and intensity maxima, springtime OH intensity enhancements at Alice Springs, and the mesospheric changes observed during the 2002 stratospheric warming event. However, the model tends to underestimate the depth of the summertime temperature minimum at both sites, possibly due to inadequate specification of the seasonal variation of gravity waves in the model. Here we present analysis of the seasonal and interannual variation of gravity waves at both Australian sites. Gravity wave data are compared to the temperature and intensity climatology, with the intent of providing better parameterization of gravity wave fluxes for TIME-GCM. Correlations between gravity wave occurrence and Australian rainfall statistics are also discussed. Gelinas, L. J., J. H. Hecht, R. L. Walterscheid, R. G. Roble, and J. M. Woithe (2008), A seasonal study of mesospheric temperatures and emission intensities at Adelaide and Alice Springs, J. Geophys. Res., 113, A01304, doi:10.1029/2007JA012587.

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Modeling the ring structures in the OH airglow layer from gravity waves excited by convection near Fort Collins, Colorado

S. Vadas1, J. Yue2, C. She2, H. Liu3, D. Thorsen4, T. Nakamura5, and S. Reising2

1: NorthWest Research Associates, CoRA division, Boulder, Colorado, USA([email protected]) 2: Colorado State University, Fort Collins, Colorado, USA 3: High Alt. Obs, NCAR, Boulder, Colorado, USA 4: University of Alaska, Alaska, USA 5: Res. Inst for Sustainable Humanosphere, Kyoto University, Kyoto, JAPAN

I will discuss the the modelling of gravity waves from convection near Fort Collins, Colorado, in the autumn of 2005: I will ray trace gravity waves modelled from thunderstorms present then to the mesospause using a newly enhanced ray trace code which includes gravity wave phases, thereby allowing for the reconstruction of the wave field. These gravity waves will be ray traced through various winds, including those from a nearby MF radar and from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). I will show that there is a threshold wind



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above which the circular gravity wave shape from thunderstorms is no longer visible near the mesopause. I will also compare the modelling results with new gravity wave data.

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Propagation and ducting of small-scale gravity waves in the mesospheric OH and O2 airglow emissions at low-latitudes

M. J. Taylor1, D. Simkhada1, J. B. Snively1, and S. J. Franke2

1: Utah State University, Utah, USA ([email protected]) 2: University of Illinois at Urbana-Champaign, Illinois, USA

Ducting is an important mechanism for the long-range horizontal propagation of gravity waves in the mesosphere, providing robust and long-lived airglow signatures of distant wave forcing. Using simultaneous imaging and background wind measurements from Maui, Hawaii (20.7N, 156.3W), during 2003, the observed and intrinsic parameters of ducted and evanescent short-period waves have been investigated. We show three examples of wave events with particularly-small horizontal scale, and compare their observed properties with theoretical predictions. The measurements were obtained using the Utah State University Mesospheric Temperature Mapper (MTM) which sequentially sampled the near-infrared OH and O2 airglow emissions centered at 87 and 94 km, respectively, and the University of Illinois meteor radar which provided continuous hourly wind measurements over the altitude range of 80-100 km. Two of the events were clearly Doppler ducted by local wind peaks for long intervals, suggesting stable duct conditions over periods of ~3 hours. The third event exhibited similar wave characteristics (wavelength, velocity and period), but was purely evanescent in nature throughout the 80-100 km region, due to large negative background winds. The ducted wave events were almost “classical” in nature fitting the theoretical Doppler ducting profiles exceptionally well.

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Long term variations and solar variability of atomic oxygen and hydrogen in the mesopause region

M. Kaufmann1, M. Ern1, C. Lehmann1, L. Hoffmann1, M. Riese1, C. v. Savigny2, M. Lopez-Puertas3, A. K. Smith4, and D. R. Marsh4

1: Institut fόr Chemie und Dynamik der Geosphaere (ICG-1), Forschungszentrum Juelich, Juelich, Germany ([email protected]) 2: Institut fόr Umweltphysik, Universitaet Bremen, Bremen, Germany 3: Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain 4: Atmospheric Chemistry Division, NCAR, Boulder, Colorado, USA

In this talk we present global measurements of the hydroxyl mesospheric airglow as observed by the SCIAMACHY satellite instrument. SCIAMACHY is mounted on ESA's Envisat launched in March 2002 into a polar, sun-synchronous orbit with an inclination of 98.7deg and an ascending node at 22:00 local solar time. Limb observations on the night side cover about 70 degree in terms of latitude during each orbit, covering 30S-70N, depending on season. This data was utilized to retrieve atomic oxygen and hydrogen profiles by means of a new OH non-LTE model. This data is analyzed with respect to solar illumination conditions and global wave activity. A windowed space-time Fourier analysis is carried out to investigate seasonal changes in mesopause wave activity. First comparisons with simulations of the NCAR ROSE model are shown.



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Long term variations in oxygen green line emission over Kiso from ground based observations using Continuous Wavelet Transform

Uma Das and H. S. S. Sinha

Physical Research Laboratory, Ahmedabad, India. ([email protected])

An analysis of 16 years long ground based photometric data of the Oxygen green line (557.7 nm) over a mid latitude station Kiso (35.79°N, 137.63°E) was made using the continuous wavelet transform technique. Climatological studies so far show that the most significant component of 557.7 nm variations is the annual component, whose magnitude increases with increasing latitude. The semi-annual component of this emission, which is much weaker than the annual component, is strongest over the equator and decreases with increasing latitude. The present study however, has shown a statistically significant semi-annual oscillation over a mid latitude station during certain epochs at 2000 hrs JST. This oscillation weakens as the night progresses and by 0200 hrs JST, it disappears completely. This feature has been observed in the WINDII measurements and also in the TIME-GCM model results and the present study forms the first proof from ground based measurements. This was not seen in the earlier analysis of same data using other mathematical techniques. There is also a strong quasi-biennial component at 2000 and 0200 hrs JST, which exceeds the semi-annual component during certain epochs, a feature not seen in previous studies using the same data. The well known annual component is also detected.

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Overturning instability in the mesosphere and lower thermosphere: analysis of instability conditions in lidar data from New Mexico and Hawaii

L. Hurd1, M. F. Larsen1, and A. Z. Liu2

1: Clemson University, Clemson, South Carolina, USA ([email protected]) 2: University of Illinois at Urbana-Champaign, Illinois, USA

The sodium lidar observations that were carried out as part of the Turbulent Oxygen Mixing Experiment in New Mexico in October 2000 were shown to have features that are consistent with the convective roll instability, as shown by Larsen et al., JGR, 2004: The instability is an inflection point instability that leads to roll circulations with time scales of several hours and cross-flow spatial scales of several tens of kilometers. The more extensive data set from the University of Illinois lidar that was operated in New Mexico first, and then later on the island of Maui in Hawaii, shows many examples of such overturning features. The high-resolution wind and temperature measurements provided by the lidar make it possible to analyze the stability of the flow at the times when the roll structures were observed. Specifically, inflection points in the vertical profile of the background winds can be identified to determine the orientation of the vertical plane where convective rolls would be expected. We present the results of the instability analysis for the extended lidar data set



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Tidal propagation of deep tropical cloud signatures into the thermosphere from TIMED observations

J. Oberheide1, and J. M. Forbes2

1: University of Wuppertal, Wuppertal, Germany ([email protected]) 2: University of Colorado, Boulder, Colorado, USA

The diurnal eastward zonal wavenumber-3 (DE3) tide is excited in the tropical troposphere by latent heat release in deep convective clouds. Its direct propagation into the thermosphere is explored using Hough Mode Extension (HME) analysis of temperature T, and zonal and meridional wind (u,v) measurements from SABER and TIDI on board the TIMED satellite. HMEs provide observation-based tidal information about parameters not measured (vertical wind w, density rho) and at latitudes and altitudes not covered by the two instruments. DE3 in (u,v,T,rho) maximizes around 100 km. The thermospheric (180 km) signal is negligible for (v,rho) but still considerable for (u,w,T). Maximum amplitudes are 6 m/s (u), 0.12 m/s (w), and 8 K (T). The HME analysis also shows the quantitative consistency of the DE3 tides from SABER and TIDI in the mesosphere/lower thermosphere region. This allows one to interpret the seasonal DE3 variation in terms of symmetric vs. antisymmetric modes.

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Tidal characteristics from the Extended Canadian Middle Atmosphere Model and comparisons with CAWSES tidal campaign results

W.E. Ward1, J. Du1, D.Y Wang1, and the CAWSES Tidal Campaign Team2

1:University of New Brunswick, Fredericton, Canada ([email protected]) 2:The CAWSES Tidal Campaign Team: W.E. Ward, Dept. of Physics, University of New Brunswick, Canada; M. Gerding Leibniz-Institute of Atmospheric Physics, Kuhlungsborn, Germany; L. Goncharenko MIT Haystack Observatory, Route 40, Westford, MA 01886 USA; P. Keckhut Service d’Aéronomie, Institut Pierre et Simon Laplace, Verrière-le-Buisson, France; D. Marsh Atmospheric Chemistry Division, NCAR, P.O. Box 3000, Boulder, Colorado 80307-3000, USA; T. Nakamura, RISH, Kyoto University, Uji, Japan; J. Oberheide Physics Department, University of Wuppertal, Wuppertal, Germany; J. Scheer Instituto de Astronomía y Física del Espacio, Consejo de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Buenos Aires, Argentina; W. Singer Leibniz-Institute of Atmospheric Physics, Kuhlungsborn, Germany; N. Grieger, Leibniz-Institute of Atmospheric Physics, Kuhlungsborn, Germany; S. Gurubaran, Indian Institute of Geomagnetism, EGRL,Tirunelveli, India; H. Takahashi, INPE, CP-515, 12245-970 Sao Jose dos Campos, SP, Brasil, P. Hoffmann, Institute of Atmospheric Physics, Germany; L. Chang, University of Colorado, USA; A. Haefele, University of Bern, Switzerland; C.-Y. She, Colorado State University, USA; T. Yuan, Colorado State University, USA

The CAWSES Global Tidal Campaigns have provided an opportunity to compare satellite and ground based observations and model results for specific observations periods. Inclusion of non-migrating modes in this comparison, results in striking agreement between the tidal signatures from these various sources. Significant variations in ground station diurnal amplitudes along the same latitude circle appear to be the result of interference between various components. Tides analysed from the extended Canadian Middle Atmosphere Model (CMAM) also show this modulation, although shifted in longitude. There are consequences for constituent transport, airglow variations and chemical heating associated with this modulation. These consequences are discussed using output from the extended CMAM. With reasonable agreement being observed in the wind and temperature fields, the next challenge for the campaign is to determine whether this agreement extends to quantities such as these.



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Thermal tides as important coupling process in the atmosphere

N. Grieger1, U. Achatz2, H. Schmidt3, and W. Singer1

1: Leibniz-Institut für Atmosphären Physik an der Universität Rostock, Kühlungsborn, Germany ([email protected]) 2: Institut für Atmosphäre und Umwelt, Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany 3:Zentrum für Marine und Atmosphären Wissenschaften, Universität Hamburg, Germany

In this paper we consider the main thermal tidal components, which are the diurnal, the semidiurnal and the terdiurnal tides with periods of 24 h, 12 h and 8 h respectively. We analyse the tides from a 20 year run of the general circulation model (GCM) HAMMONIA, including chemical interactions, which covers the atmosphere up to about 250 km height, for minimum solar radiation condition. Using the linear model LIN-KMCM with monthly mean background fields in wind and temperature, and the thermal forcings derived from the GCM we can show that the tides simulated by the linear model and the GCM tides are in good agreement with satellite observations. The vertical structure of the diurnal tides shows a wavelike structure with wavelengths of about 27 km concentrated around subtropical latitudes. The largest amplitudes of the semidiurnal and terdiurnal tides are located above the MLT in higher latitudes with values of about 40m/s and 10m/s for the meridional wind. The vertical wavelength for the 12h tide is at 50° of the order of 50km. The vertical structure of the 8h tide seems to be more barotropic.

With the linear model we study for the three main tidal components the dependence of seasonal variations on the tidal forcing processes, on the background winds, and the planetary waves. The results are discussed both for the migrating and the nonmigrating components (i.e.: sun synchronous and non-sun-synchronous travelling waves). It can be shown that the largest influence is due to the monthly mean wind variations throughout the year, but for the nonmigrating components the stationary waves can be shown to be very important as well.

We discuss the influence of different forcing levels on the seasonal tidal variations in the MLT. The most important process to form the diurnal tides is located in the troposphere, whereas the semidiurnal tides due to forcings in the stratosphere interfere with those ones forced in the troposphere. The first part would lead to tides 2.5 times larger than in the complete case, while the second one contributes negatively with amplitude 1.5 times larger than in the complete case. These interactions between tides forced in different altitudes show the strong coupling between lower atmospheric levels and the MLT region by tidal propagation.

Finally we study the coupling processes at low and high latitudes using wind observations from meteor radars at Learmonth (114°E, 22°S) and Andenes (16°E, 69°N), and compare them with tides analysed from GCM and LIN-KMCM outputs.



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Estimates of momentum deposition on the diurnal tide

R. Lieberman1, J. Oberheide2, D. Riggin1, and R. Stockwell1

1: Northwest Reserach Associates, Colorado Research Associates Division, USA ([email protected]) 2: University of Wuppertal, Germany

Migrating diurnal amplitudes show intense seasonal and year-to-year variations. Momentum deposition and turbulent diffusion by small-scale gravity waves and/or larger scale wave-wave interactions have been suggested as possible mechanisms. Numerical estimates of these effects have relied upon gravity wave parameterization, and experiments with general circulation models. This study infers the mechanical forcing upon the diurnal zonal wind using satellite-based estimates of tidal winds, temperatures, and the zonal mean wind. We compute the zonal momentum residual as a Rayleigh drag term using High Resolution Doppler Imager (HRDI) data from 1993--94: The Rayleigh coefficient KR is complex, with real components that are positive and negative. This implies that the net momentum forcing upon the tides can increase or decrease amplitudes, and modify the vertical wavelength. The real part of KR is typically ±2 day $\sp{-1}$, which is an order of magnitude higher than values inferred from parameterized gravity wave drag. Our estimates of KR are consistent with positive definite values obtained in the model tuning experiments of Khattatov et al. Our values are also similar to those computed by McLandress for the stress exerted upon the diurnal tide by large-scale wave-wave interactions.

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Planetary waves and tides observed by TIMED/SABER in coupling the stratosphere-mesosphere-lower thermosphere during the major stratospheric

warming in 2003/2004

D. Pancheva1,2, P. Mukhtarov1 and B. Andonov1

1: Geophysical Institute, Bulg. Acad. Sci., Sofia, Bulgaria ([email protected]) 2: CSAOS, University of Bath, Bath, UK

The sudden stratospheric warming (SSW) is a violent large-scale thermo-dynamical phenomenon in the winter polar region, which strongly affects the middle atmosphere (≈ 20-100 km). It is caused by the interaction of the mean atmospheric circulation with transient planetary waves (particularly quasi-stationary planetary waves) originating mainly in the lower atmosphere. The present study is focused on the vertical coupling due to planetary waves and tides observed in the Northern Hemisphere atmosphere between 30 and 120 km height during the winter of 2003/2004. The emphasis is on the major SSW beginning in late December 2003, which led to nearly two months of vortex disruption. The TIMED/SABER data for the period 1 October 2003-31 March 2004 have been used to identify the planetary waves and tides in the temperature field of the Northern Hemisphere (0-50oN). A new method for analysis of satellite data is used where the migrating and nonmigrating tides and planetary waves (stationary, zonally symmetric and traveling) are simultaneously extracted from the satellite data. The main advantage of this method consists in avoiding a possible distortion of the weaker waves by the stronger ones, as well as some aliasing effects between the tides and stationary planetary waves. The main traveling and stationary planetary waves, extracted from the SABER data, have been compared with the same waves extracted from the UK Met Office (UKMO) temperature data for altitudes up to 60 km. The comparison between the altitude and latitude structure of the SABER and UKMO planetary waves in the temperature field of the NH stratosphere indicated a high degree of qualitative and



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quantitative resemblance and in this way the validity of the data analysis method has been verified as well. The altitude and latitude structure of the SABER planetary waves clearly indicated that the stratosphere and mesosphere (30-90 km) are coupled by direct vertical propagation of the planetary waves, while the lower thermosphere (above 90-95 km altitude) is only partly connected with the lower levels indirectly trough in situ generation of disturbances by the dissipation and breaking of gravity waves filtered by lower atmospheric planetary waves. The temporal evolution and spatial structure of the migrating and nonmigrating 24- and 12-h tides with zonal wavenumbers up to 4 have been studied as well. The emphasis was on the nonmigrating tidal activity related to the major SSW in the Arctic winter of 2003/2004.

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Mesospheric/lower thermospheric winds, tides and mesopause temperatures at low latitudes from meteor radar and satellite observations

W. Singer1, P.P. Batista2, J. Oberheide3, T. Nakamura4, P. Hoffmann1, B.R. Clemesha2, R.A. Buriti5, D. Riggin6, and G. Ramkumar7

1: Leibniz Institute of Atmospheric Physics, Kuehlungsborn, Germany ([email protected]) 2: National Space Research Institute-INPE, Sao Jose dos Campos, SP, Brazil 3: Physics Department, University of Wuppertal, Wuppertal, Germany 4: Research Institute for Sustainable Humanosphere-RISH, Kyoto University, Kyoto, Japan 5: Universidade Federal de Campina Grande, Paraiba, Brazil 6: Northwest Research Associates, Boulder, CO, USA 7: Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India

Winds at mesospheric/lower thermospheric altitudes between 80 and 100 km and temperatures around 90 km are derived from all-sky meteor radar observations at latitudes between 9°N and 22°S and longitudes between 77°E and 315°E. The data are acquired with identical radar systems and detection software. The six SKiYMET radars are located at Trivandrum (9°N, 77°E), Kototabang (0.2°S, 100°E), Cariri (7°S, 323°E), Learmonth (22°S, 114°E), Rarotonga (21°S, 200°E), and Cachoeira Paulista (22°S, 315°E). Wind tides are determined for the year 2005 using 4-d, 10-d, and 60-d composite days. The results provide information about the variability of the diurnal, semi-diurnal, and ter-diurnal tide at low latitudes. The seasonal variability of mean winds, temperatures, and tides is discussed. For the latitude 22°S the seasonal variation of the migrating tides is estimated using the observations at three sites which are well separated in longitude. The radar results obtained from 60-d composite days agree well with diurnal tides derived from TIDI observations on the TIMED satellite. The tidal signatures derived during the first measurement campaign of the CAWSES Global Tidal Study in September/October 2005 at low latitudes are discussed in relation with observations at middle and high northern latitudes.

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Equatorial middle atmosphere wind observations with Jicamarca meteor radar

L. Guo, G. Lehmacher

Clemson University, South Carolina, USA ([email protected])

Jicamarca All-sky Specular Meteor (JASMET) VHF radar was installed in Jicamarca, Peru (11.95°S, 76.87°W) in 2005 and the first campaign was conducted in June 2006: Various parameters including wind and ambipolar diffusion coefficient can be derived from meteor trail echoes. Details of the equipment,



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recent experiments, data analysis and the first results of the equatorial MLT wind observations from monthly measurements in 2006 to 2008 between 70 to 110 km will be presented and the estimated tidal components will also be compared with those from GSWM.

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On the seasonal dependence of midlatitude sporadic E layers

C. Haldoupis

Physics Department, University of Crete, Greece ([email protected])

The midlatitude sporadic E layers (Es) form when metallic ions of meteoric origin in the lower thermosphere converge vertically in a wind shear under the combined action of geomagnetic Lorentz and ion-neutral collisional forces. A key property of Es is its seasonal dependence that is marked by a pronounced summer maximum. This seems to be inexplicable from the wind shear theory of Es formation and the physical reason behind remained a mystery since the early years of ionosonde studies. Recently, Haldoupis et al. (JGR, 112, doi:10.1029/ 2007JA012322) suggested a likely explanation by showing that the summer maximum in Es correlates well with the peak of sporadic E meteor deposition in the upper atmosphere. This was obtained by analysing routine ionosonde recordings and simultaneous daily meteor count rates, measured in the northern hemisphere with a meteor radar interferometer, and by adopting that the layer occurrence and strength depend directly on the available metal ion content, which must be determined primarily by the meteoric deposition. In this work we investigate further the relation between the seasonal variations in sporadic E critical frequency foEs (which characterizes the Es strength) and the meteor deposition by using measurements made at arctic, equatorial and antarctic latitudes with SKYiMET meteor radars. The extended data sets used for analysis led to the identification of similarities but also differences that exist in the seasonal variability of the two parameters. The results revealed some complexities which exist and raise questions that need to be addressed. It appears that on the average the long-term meteor deposition correlates well with the annual dependence of sporadic E, especially with respect to the strong summer maximum, but the correlation erodes during fall and is absent during intervals of dominant meteor showers.

Aknowledgements: The meteor observations used in the analysis were provided by Peter Younger University of Bath, UK.

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Thermospheric meridional winds as deduced from ionosonde network and midnight temperature maximum

T. Maruyama, S. Saito, M. Kawamura, and K. Nozaki

National Institute of Information and Communications Technology, Tokyo, Japan ([email protected])

Multipoint ionosonde observation was conducted in Southeast Asia to study the ionosphere-thermosphere system. For this observation three ionosondes were installed along the magnetic meridian at 100deg.E (Southeast Asia Low-latitude Ionospheric Network: SEALION); two of them were at magnetic conjugate points at low latitudes and the third was near the magnetic equator. The F-layer virtual height, h’F, was scaled from nighttime ionograms obtained from September 2004 to August 2005: Height variations over the equatorial station were used to estimate the vertical EXB drift velocity. In conjunction with the equatorial vertical EXB drift velocity, no-wind heights over the two low-latitude stations were calculated by an ionospheric modeling technique. Differences between the observed height and the modeled no-wind



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height were used to estimate the thermospheric winds in the magnetic meridional plane for transequatorial and convergent/divergent components (both with respect to the magnetic equator).

The nighttime wind variations broadly agreed with a seasonal pattern blowing from the summer hemisphere to the winter hemisphere and convergence toward the equator. In addition to these general tendencies, higher order local time variations with a period of 6-8 hours were found. The amplitude of the higher order variations was significant in the northern winter months. In the previous works, higher order variations of the meridional wind are attributed to the pressure bulge associated with the midnight temperature maximum (MTM). However, integrating the present and previously reported results, we did not find any evidence showing abatement of the equatorward wind associated with the MTM. On the other hand, a clear correlation was found between the convergent wind and the MTM observed by the AE-E satellite. The adiabatic compression heating scenario of the thermospheric temperature and the absence of the wind abatement are consistent with the simulations by Fesen [JGR, 1996] and Corelico et al. [JASTP, 2002] using the NCAR-TIEGCM. Those authors also suggest that higher order terms of the wind variation are required to obtain sufficient amplitude of the MTM as observed and the wind abatement. We have observed higher order variations of the thermospheric wind, nevertheless no clear evidence of wind abatement was found. Most probably the higher order variations propagate from the lower atmosphere, but are not generated in the thermosphere.

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The equatorial thermospheric anomaly: Update on analysis of measurements from the ionization gauge on the Streak mission

J. Clemmons

The Aerospace Corporation ([email protected])

Presented is new work based on analysis of measurements returned by the ionization gauge flown on the Streak mission. The work extends the previously-reported observations of thermospheric neutral density structure organized by the geomagnetic field at low latitude and altitudes below 330 km. These measurements reveal structure similar to the long-known equatorial ionization anomaly (EIA) – thus the term equatorial thermospheric anomaly (ETA) is used. Although the similarities are obvious, so are several important differences, including displacement of the density maxima, movement of the maxima with season, and variation of the magnitude of the maxima. The results are interpreted in light of results from previous missions, including CHAMP, and possible theoretical explanations.


Poster P1: Posters for Session S3 (Equatorial Lower- and Middle- Atmosphere Studies)

64

Analysis of March 29 2006 eclipse on the E and F1 region at Ilorin

J. O. Adeniyi1, S. M. Radicella2, I. A. Adimula1, O. A. Oladipo1, O. Olawepo1, and A. A. Willoughby1

1: Physics Department University of Ilorin, P.M.B. 1515,Ilorin Nigeria ([email protected] and [email protected]) 2: The Abdus Salam International Centre for Theoretical Physics, Aeronomy and Radio Propagation Laboratory, Trieste.

The ionograms recorded at Ilorin, Nigeria (Longitude 4.57oE, Latitude 8.53oN, Dip 4.1oS), an equatorial station in West Africa, on the March 29 2006 eclipse day were analysed. The eclipse effects on the morphology of the ionosphere were observed. The data obtained on the eclipse day were used along with those of the control day to determine photochemical rates in the E and F1 regions of the ionosphere.

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Planetary waves in the equatorial electrojet obtained by wavelet wnalysis of magnetometer data

H. C. Aveiro, C. M. Denardini, and M. A. Abdu

Inst. Nacional de Pesquisas Espaciais, S. J. Campos, SP, Brazil ([email protected])

The approximate effect of the equatorial electrojet (EEJ) magnetic field over the H-component of the Earth’s magnetic field can be investigated analyzing the diurnal variation of this magnetic component obtained by magnetometers (ΔH). To study the planetary wave oscillations in the EEJ we have select magnetically quiet days ensuring that the variations in the ΔH were caused mainly by the electrojet and Sq current system. We have calculated (ΔHEEJ), the difference of the H-component variations at the two close by magnetic stations to remove external source like the Sq current system effects and magenetospheric currents. Once São Luís Space Observatory (2.33° S, 44.2° W, DIP: -0.5) is located on a region of EEJ influence and the Magnetic Observatory of Eusébio (3.89° S, 38.4° W, DIP: -12.5) is located outside the electrojet region, the resultant difference (ΔHEEJ =ΔHSLZ - ΔHEUS) is supposed to contain only the EEJ influence. We performed a wavelet analysis using the Morlet wavelet-mother and obtained the periodicities vs. time. Studies using magnetometer data in other magnetic stations have confirmed the presence of 2-, 5-, 10- and 16-days electro-dynamical signatures possibly due to the interaction between planetary waves with the ionospheric dynamo region. In this paper, we analyze the agreement between the planetary waves occurrences in Brazilian region and results obtained in earlier papers, related to other regions of the world.

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The March 29, 2006 solar eclipse as observed at Ibadan, Nigeria

M.A. Ayoola1, G. I. Olatona2, E. O. Oladiran1, and J. A. Adedokun3

1: Department of Physics, University of Ibadan ([email protected]) 2: Department of Physics, Osun State College of Education Ilesa. 3: Department of Physics, Obafemi Awolowo University, Ile-Ife.

During the solar eclipse of March 29, (Julian day 88) 2006, an unstable stratification of the air mass was observed at Ibadan (7.380 N, 3.930E) Nigeria. The radiation and temperature sensors and other



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temperature probes at Nigerian Meteorological Experiment (NIMEX) site located at the station provided a general overview of the energy fluxes, the winds and the cloud situation not only at the short period of the solar eclipse but before and after the event. The observed minimum temperature and wind at the site during the eclipse were comparable to those of the previous days. The corresponding values of radiative energy fluxes measured before the day of the eclipse was as high as 642 Wm-2. This fell bellow 30 Wm-2 during the eclipse period at the site. The mean wind speed which was as low as 0.50 ms-1 established the fact of the calmness in wind speed that characterized the period of solar eclipse. These minimum values were unusual compared with those obtainable during any clear sky conditions. This variation may have induced vertical exchange of air parcels in the atmosphere.

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Observations of zonal and meridional winds and diurnal and semidiurnal tides at 7.4°S by a meteor radar

R. A. Buriti1, W. K. Hocking2, P. P. Batista3, A. F. Medeiros1, and B. R. Clemesha3

1: Universidade Federal Campina Grande, Campina Grande, Brazil ([email protected]) 2: University of Western Ontario, London, Ontario, Canada 3: Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP, Brazil

Mesospheric winds between 82 and 98km were observed between July 2004 and June 2005 with a meteor radar installed at Cariri (7.40S, 36.50W), Brazil. The data showed a clear semiannual oscillation known as Mesospheric Semiannual Oscillation (MSAO) with maximum amplitude of 22.6m/s in the zonal wind at 82km decreasing up to 3.3 m/s at 98km of altitude. Maximum westward winds were observed in March and September. On the other hand, the meridional wind, showed a clear annual variation with maximum amplitude of 13.5m/s at 98km. Maximum northward winds were observed practically in December. Additionally to mesospheric wind results, diurnal and semidiurnal parameters were calculated to zonal and meridional components. It is worth to emphasize the semiannual oscillation of diurnal tide observed in the zonal wind at 98km with maxima at the equinoxes. Other results of the analyses of the data and comparisons with models will be present

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Role of equatorial anomaly in assertion of low latitude earthquake-perturbations on ionosphere

M. Devi 1, A.K. Barbara 1, Yu. Ruzhin 2, A. Depueva 2, and V. Depuev 2

1: Department of Physics, Gauhati University, Guwahati 781 014, Assam, India([email protected]) 2: Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow region, Russia

The paper implicates a series of observations on ionization density (foF2) & TEC from ionosonde and GPS systems, to address the involution of equatorial anomaly in assertion of earthquake induced perturbations at the ionosphere. Adapting a pool of data acquired in this process around the equatorial anomaly crest stations, we bring in here the act of inducing low latitude seismic-related disturbances to off epicenter position, through anomaly effect when relative position between epicentre and observing station is (i) within the distance (d) dictated by the equation d = exp M (km), where M is magnitude of earthquake. We also examine (ii) cases when the radial distances exceed this limit.



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The admission processes of earthquake preparatory effects in modifying ionospheric features are defined here in four temporal periods (pre-morning, noon, post noon, and post sunset) and symptoms on seismic-influenced anomaly effect are pulled out as precursor features. These characteristics are recorded on adopting filtering & screening approaches from quiet day parameters, individually for each defined time frame. The main predictor parameter obtained as “enhancement followed by depletion” in density and TEC, from a few days to the event days, are discussed invoking the role of seismic related E-field working with normal fountain processes. More than 20 earthquake events with radial distance defined as has been mentioned above are presented. For Guwahati, a seismically active area on Himalayan region, for the 13 cases (M≥5), the prediction is good.

For the case (ii), it is interesting to note that the above precursor characteristics are also recorded at the observing location, if a small magnitude earthquake (M = 4÷5) is present within the zone dictated by afore-said equation. The observation is presented through more than ten events. However the dynamical and physical processes are not yet clear.

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Climatology of low-latitude mesospheric dynamics using Gadanki VHF radar, rocket, and HRDI

G. Kishore Kumar1, M. Venkat Ratnam2, A. K. Patra2, S. Vijaya Bhaskara Rao1, K. Kishore Kumar3, S. Gurubaran4, G. Ramkumar3, and D. N. Rao5

1: Department of Physics, Sri Venkateswara University, Tirupati – 517 502, India 2: National Atmospheric Research Laboratory (NARL), Post box No: 123, Gadanki, Tirupati – 517 502, India. ([email protected]) 3: Space Physics Laboratory, Vikram Sarabhai Space Center, Thiruvananthapuram, India 4: Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India 5: RISH, Kyoto University, Japan

Low-latitude mesospheric dynamics like, echo characteristics, lifetime of mesospheric echoes, and the background mean winds are studied using 11 years data collected by the Indian MST radar located at Gadanki (13.50N, 79.20E). Mesospheric echoes are highly intermittent both in space and time. These echoes are frequently observed between 1000-1530 hrs LT in the height region of 68-78 km. Both the percentage occurrence (PO) of echoes and SNR show Semi-Annual Oscillation (SAO) with maxima during equinoxial months. The mechanisms behind the observed features are discussed in the light of mesospheric temperature inversions (MTIs), which are often noticed at this location using Nd: YAG Rayleigh lidar and wave breaking at these altitudes. In general, the echo persistent time is less than 20 minutes, between 20-40 minutes, and above 40 minutes for 70-90%, 10-20% and 5-15% of the time, respectively. The persistent times also show clear seasonal variation. The high persistent echoes are observed mainly in the height region of 70-80 km. Based on the observations of echo persistence time, it is possible to classify/quantify the turbulence structures in between 65-85 km.

Using the Doppler shift of the mesospheric echoes, the background wind is estimated. These winds are compared with the other observations like rocket, HRDI, MF radar and with HWM93 model. All these comparisons are good in agreement except the MF radar winds. Reasons are being investigated by considering the limitations of the techniques. A clear semiannual oscillation is observed in mesospheric zonal wind maxima during equinoxial periods. The first peak of the SAO is larger than the second peak of the SAO and these results are consistent with the earlier observations. The significance of the present result lies in showing the consistency/inconsistency of various experimental techniques to measure the middle atmospheric winds, which are very important to assess the climate variability.



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Using the long term data set from Rocket, MF radar and VHF radar spanning three decades, few climatological changes have been observed in the mesospheric mean winds such as decrease in winter eastward wind, mesospheric QBO and SAO. Details will be presented during symposium.

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Study of mesospheric turbulence using rocket-borne electron density measurements

H. S. S. Sinha, Uma Das, R. N. Misra, M. B. Dadhania, Swaroop Banerjee, and N. Dutt

Physical Research Laboratory, Ahmedabad, India. ([email protected])

A rocket-borne Langmuir probe was flown from Thumba on November 27, 2005 at 1123 hrs IST to study the mesospheric plasma density irregularities produced through the neutral turbulence mechanism. The Langmuir probe detected electron density irregularities with scale sizes in the range of 1m to a few km in altitude range of 67 to 90 km during the rocket ascent. The altitude-averaged (over 100 m) power spectra from wavelet spectrograms of electron density irregularities show spectral indices ranging from -1.5 to -1.9 in the inertial sub range (ISR) and greater than -3.5 in the viscous dissipation range (VDR). The spectral index values in the ISR are very close to the characteristic Kolmogorov -5/3 slope due to neutral turbulence. The Heisenberg model was fit to spectra that showed the presence of both the ISR and VDR regimes and the inner scale was identified. The turbulence parameters were then deduced. The observed energy dissipation rates in the above altitudes range from few mW/kg to few hundreds of mW/kg.

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Gravity waves sources in the Brazilian equatorial region during SpreadFEX campaign

C. M. Wrasse , J. Fechine2, H. Takahashi3, A. F. Medeiros2, J. V. Bageston3, C. M. Denardini3

1: Universidade do Vale do Paraíba, IP&D, São José dos Campos, SP, Brazil ([email protected]) 2: Universidade Federal de Campina Grande, UFCG, Campina Grande, PB, Brazil 3: Instituto Nacional de Pesquisas Espaciais, INPE, São José dos Campos, SP, Brazil

Gravity waves in the mesosphere were observed by airglow all-sky imaging technique at São João do Cariri (7ºS, 36ºW) from September to November 2005, during SpreadFEX campaign carried out in Brazil. A reverse ray tracing method was used to find out wave source region and to study propagation process through the middle atmosphere. Ray tracing results showed that the wave source regions in the troposphere are located 500 km away from the observation site mainly in NW and SW side of the observatory. Tropospheric sources were related with the cloud activity observed in the infrared images taken by METEOSAT satellite. Wind field and Omega (Pa/s) parameter was used to study a special case of a gravity wave with a horizontal wavelength of 120 km and period of 42 minutes. The results showed that the source location of this wave is located at NW site of the observatory, distant more than 700 km away. Source region found with the ray tracing technique is in good agreement with the observational data taken by the infrared images, wind field and Omega (Pa/s). The possible generation mechanism for this wave could be attributed to the dynamic instability caused mainly due to the vertical wind shear observed in the Omega data.



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Gravity waves activities in the stratosphere and mesosphere over the Brazilian equatorial region

C. M. Wrasse1 , H. Takahashi2, J. Fechine3, A. F. Medeiros3, J. Wickert4, C. M. Denardini2

1: Universidade do Vale do Paraíba, IP&D, São José dos Campos, SP, Brazil ([email protected]) 2: Universidade Federal de Campina Grande, UFCG, Campina Grande, PB, Brazil 3: Instituto Nacional de Pesquisas Espaciais, INPE, São José dos Campos, SP, Brazil 4: GeoForschungsZentrum, GFZ, Potsdam, Germany

Gravity wave activities in the stratosphere are deduced from GPS radio occultation temperature profiles obtained by CHAMP satellite. The potential energy profiles are used to analyse the gravity wave activity, seasonal variability and possible wave sources. Mesospheric gravity wave observations, using all sky imager, are compared with the stratospheric potential energy in order to investigate the gravity wave occurrence. The results show that the gravity wave activity over Brazil is strongly correlated with mesosecale synoptics systems that produce deep convection, such as mesoscale convective systems, squall lines, cold fronts and the Intertropical Convergence Zone.


Poster P1: Posters for Session S4 (Equatorial and mid-latitude MLT dynamics)

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A comparative study of the quasi-2-day wave observed at 7.4° S and 22.7° S, Brazil, during summertime

L. M. Lima1, H. Takahashi2, B. R. Clemesha2, P. P. Batista2, and C. M. Wrasse3

1: UEPB, Campina Grande-PB, Brazil ([email protected]) 2: INPE, S. J. dos Campos-SP, Brazil 3: IP&D/UNIVAP, Brazil, S. J. dos Campos-SP, Brazil

From simultaneous observations of the atmospheric neutral winds in the mesosphere and lower thermosphere (MLT) region by meteor radar carried out at São João do Cariri (7.4° S, 36.5° W) and Cachoeira Paulista (22.7° S, 45.0° W), we have investigated the planetary-scale quasi-two-day wave, which are present in both the sites during 2005 and 2006 austral summers. Amplitude of the meridional component was larger than that of the zonal component, reaching the maximum value of ~50 m/s. The phase propagation with height shows a descending mode and vertical wavelength estimated for Cachoeira Paulista was longer than at São João do Cariri, for all of the observed events. Significant changes on the mean zonal wind can be observed as suggestive of the quasi-2-day wave impact. Spectral analysis for meridional winds shows the presence of additional peaks with periods near 16 hours, suggesting nonlinear coupling between the 2-day wave and the diurnal tide in the equatorial MLT region. Cross-correlation and bispectral analysis supports the existence of the relationship between the quasi-two-day-wave and the diurnal tide.


Special Lecture of General Interest

70

The Antikythera Mechanism

John H. Seiradakis

Aristotle University of Thessaloniki, Department of Physics, Laboratory of Astronomy

The Antikythera Mechanism was found by chance, in a shipwreck, close to the small Greek island of Antikythera (between Crete and Peloponnese) in April 1900, by sponge divers. The shipwreck was dated between 86 and 67 B.C. (coins from Pergamon). The Mechanism has been dated, by epigraphologists, around the second half of the 2nd century B.C. (100 – 150 B.C.). About this time the great Greek astronomer Hipparchos (190 – 120 B.C.) lived in Rhodes. It was a portable (laptop-size), geared artifact which calculated and displayed, with high precision, the movement of the Sun and the Moon on the sky, the phase of the Moon for a given epoch and could predict eclipses. It had one dial on the front and two on the back. Its gears were driven by a manifold, with which the user could set a pointer to any particular epoch (at the front dial). While doing so, several pointers were synchronously driven by the gears, to show the above mentioned celestial phenomena on three accurately marked annuli. It contained an extensive user’s manual. The exact function of the gears has finally been decoded and a large portion of the manual has been read after 2000 years by a major new investigation, using state of the art equipment.


Session S5: E-region plasma physics

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Lessons learned observing Farley Buneman waves at low, middle, and high latitudes

D. L. Hysell1, G. Michhue1, M. F. Larsen2, R. Pfaff3, and J. L. Chau4

1: Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA ([email protected]) 2: Physics and Astronomy, Clemson University, Clemson, SC, USA 3: NASA Goddard Space Flight Center, Greenbelt, MD, USA 4: Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima, Peru

Farley Buneman waves have been observed in the equatorial, midlatitude, and auroral E regions using imaging coherent scatter radars. The interpretation of the observations from these latitude regimes is obfuscated by large-scale waves, sporadic E layer properties, and wave heating, respectively (to name but a few potential complications). A unified picture regarding the interpretation of the Doppler spectrum of Farley Buneman waves is emerging from the combined radar observations, viewed in the light of recent rocket experiments and numerical simulations. In particular, the Doppler shift and spectral width appear to be predictable and perhaps invertible functions of the convection electric field. A ground-based diagnostic of fine structure in the auroral convection pattern based on Farley Buneman wave observations should be realizable.

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Inelastic electron energy exchange and altitude behaviour of a phase velocity spectrum of Farley-Buneman waves for equatorial electrojet∗

L.M. Kagan and R.S. Kissack

University of Western Ontario, London ON, Canada ([email protected])

Based on our linear theory of the Farley-Buneman (FB) instability which includes thermal corrections and accounts for non-zero aspect and flow angles [Kissack et al., Phys. Plasmas, 2008a,b, in press], we have developed a simplified formula for the phase velocity Vph of FB waves as function of a wave frequency and ionosphere parameters (altitude). For altitudes 100-110 km, the simplified solution gives less than a 3% deviation from the full solution found numerically. The formula allows for quick estimates of Vph and understanding of the physical processes dominating the FB wave behaviour at different altitudes. We show that FB wave altitude behaviour changes from super-adiabatic at lower altitudes to isothermal at high altitudes. Depending on the FB wave frequency, the transition from super-adiabatic to isothermal behavior may go either via a transitional process dominated by inelastic electron energy exchange for lower frequencies (e.g. 16 and 50 MHz) or directly for higher frequencies (e.g. 150 MHz and higher). In order to test our theoretical predictions we present a case study of 3-frequency observations of FB waves in the equatorial electrojet over Jicamarca reported by Balsley and Farley [J. Geophys. Res., 76(34), 8341-8351, 971]. Remarkably, this 38-year old data set remains the only observations of FB waves at more than two frequencies. The radar backscatter was received from 60° east off vertical at 16, 50 and 146 MHz in sequence. The similarity of radar returns at the same frequency allowed Balsley and Farley to conclude ∗ based on Kagan, L. M., and R. S. Kissack (2007), Geophys. Res. Lett., 34, L20806, doi:10.1029/2007GL030903.



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that the radar probed the same ionospheric volume. Because the signal was averaged over entire electrojet, we based our comparison of the theory and observations on the frequency dependence. Our theoretical predictions match observations remarkably well.

A very important byproduct of this case study is our conclusion that the energy exchange rate parameter for inelastic electron-neutral interactions, eδ , is about two-to-three times higher that it has been

assumed in most earlier work ( eδ =0.003). We show that a more than doubled eδ could lead to a

different dominating process at the lower frequencies of 16 and 50 MHz and significantly extend the altitude range where inelastic electron cooling plays crucial role. At 16 MHz, for example, wave behaviour is dominated by inelastic electron energy exchange at all altitudes of interest for 0.007eδ = ,

while for 0.003eδ = inelastic electron interactions are important only above 104 km and FB waves

behave super-adiabatically below 104 km. At 50 MHz, the altitude range dominated by the transitional process (the process governed by inelastic electron interactions) becomes significantly shorter and starts at higher altitudes. At 146 MHz, thermal conduction and Doppler terms significantly exceed inelastic electron cooling; therefore actual value of eδ does not play any role, resulting in a very rapid decrease in

Vph with altitude and switching to the isothermal regime directly from the super-adiabatic. In our companion talk Kagan2-S5-N we discuss the latter case in greater detail.

This research has been supported by the Canadian Natural Sciences and Engineering Research Council.

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The speed of type I and other fast moving echoes in the ionospheric E region

J.-P. St.-Maurice

University of Saskatchewan, Canada ([email protected])

Recent observations of irregularities both at low and high latitudes seem to indicate that the saturation speed of irregularities is not as simple as we originally thought. In particular, the ion-acoustic speed has been used as a benchmark to describe the speed of so-called “Type I” irregularities both at high and low latitudes. A closer look, however, reveals that, during strongly driven events at least, equatorial Type I irregularities move faster than the ion-acoustic speed, even along the vertical direction. Sometimes the speed clearly increases as the altitude decreases. In other observations, this feature is not that clear, but the speed remains tantalizingly faster than the ion acoustic speed. At high latitudes, particularly in the presence of very strong electric fields, narrow fast echo signatures called “Type IV” are seen to accompany what seems to be a “heated” Type I echo. We have now made theoretical advances that show that non-isothermal electron behaviour plays an important role in the determination of the threshold speed in situations where the wavevector is very close to perpendicularity to the magnetic field. At low latitudes, a combination of small aspect angles and large collision frequencies at lower altitudes leads to important non-isothermal corrections to the ion-acoustic threshold speed, which matches some observations rather well. At high latitudes, we propose that Type IV echoes are produced at a stage where the echoes grow slowly in the presence of unfavourable gradients, thereby explaining the narrow spectral widths often seen in these cases. In a second stage of evolution, the echoes start to rotate appreciably and evolve a parallel electric field which suddenly forces the phase speed to rapidly decrease to the isothermal ion-acoustic speed. In other cases, however, there is no sign of increasing speeds with decreasing altitudes to indicate that non-isothermal effects are taking place. Nevertheless, recent Cornell observations have shown that the speed of the smallest aspect angle echoes appears to be noticeably faster than the ion-



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acoustic speed. When observed along the vertical, these echoes are all the more remarkable because they have to be created inside a field that comes from the vector combination of a vertical ambient electric field and a horizontal field from a gradient-drift structure. Therefore, vertical Type I echoes should not be as easily excited along the vertical than along some finite oblique angle. With narrow spectra in these cases indicating weak turbulence, one is left to wonder if in fact we are not just observing echoes that are at a linear stage of their evolution, particularly when the aspect angle is very small. Larger aspect angles might evolve in the way they do at high latitudes, as a result of a rotation in large amplitude Type 1 structures that will be leading to the creation of finite aspect angles through the inhomogeneities in the background atmosphere that are bound to exist (for instance, the ever-present gravity waves come to mind as a source for these inhomogeneities).

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Hybrid-model simulations of Farley-Buneman instability with electron thermal effects

D. Kovalev1, A. Smirnov1, and Y. Dimant2

1: Moscow State University, Moscow, Russia 2: Center for Space Physics, Boston University, Boston, USA ([email protected])

The Farley-Buneman (FB) instability is a two-stream low-frequency plasma instability observed in the E-region ionosphere where electrons are magnetized, while ions are demagnetized due to frequent collisions with neutral particles. The instability is caused by a sufficiently strong electric field perpendicular to a magnetic field and is usually excited in the equatorial and high-latitude electrojets.

Nonlinear simulations of the FB instability are usually based on fully kinetic, particle-in-cell (PIC), or hybrid fluid isothermal for electrons, PIC for ions codes. Our novel hybrid approach is based on solving fluid equations for electrons and a kinetic equation for ions with the Bhatnagar-Gross-Krook (BGK) collision term. The advantage of this kinetic equation is that it includes the crucial effect of ion Landau damping while avoiding numerical noises associated with the finite number of randomly moving particles. Fluid description of electrons allows modeling the real electron mass.

For a more realistic description of the Farley-Buneman instability our model was extended to non-isothermal electrons. This allows us to analyze influence of the electron thermal effects on the instability. Simulations show that the development time of the instability increases and the value of the turbulent electric field in the saturation decreases under assumption of non-isothermality.

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Large-Scale Simulations of Farley-Buneman Turbulence in 2D and 3D

M. M. Oppenheim1, Y. S. Dimant1, and L. P. Dyrud2

1: Center for Space Physics, Boston University, Boston, USA ([email protected]) 2: Center for Remote Sensing, Arlington, VA, USA

In the E-region ionosphere, turbulent processes driven by strong ambient DC electric fields create plasma density irregularities responsible for type 1 radar echoes. These irregularities play a role in ionospheric conductivity, temperatures, and radio wave propagation and reflectivity. As a result they have been studied experimentally and theoretically for five decades. In the last decade, numerical simulations became an important tool in exploring the nonlinear behavior of E-region instabilities. However, these simulations were limited to 2-D and meshes resolving typically around 4096 (64x64) cells. Having



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improved the method of parallel processing of our Particle-In-Cell (PIC) code, EPPIC, we can now take advantage of supercomputers with thousands of processors to run simulations with enormous meshes in 2-D or 3-D (up to 8092x8092 in 2D or 512x512x512 in 3-D).

Recent 2D simulations show the saturated amplitude of the waves; coupling between linearly growing modes and damped modes; the evolution of the system from dominance by shorter (1m-5m) to longer (10m-200m) wavelength modes; and the propagation of the dominant modes at phase velocities that lie below the linearly predicted phase velocity and close to but slightly above the acoustic velocity. These simulations reproduce many of the observational characteristics of type 1 waves. As predicted by theory, the 3-D simulations show the development of modes with a small component parallel to the geomagnetic field. Nevertheless, the 2-D and 3-D runs develop similar spectral features. We also can quantify the 3-D wave-driven electron heating, a phenomena clearly observed by radars. These simulations provide information useful in accurately modeling FB turbulence and demonstrate the significant progress we have made simulating the electrojet.

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What two-step Type I waves reveal about equatorial E region turbulence.

R.K. Choudhary1 and J.-P St.-Maurice2

1: Space Physics Laboratory, VSSC, Trivandrum, India ([email protected]) 2: ISAS, University of Saskatchewan, Saskatoon, Canada ([email protected])

It is now well understood that large scale (km) horizontally propagating gradient-drift structures are at times strong enough to excite short scale (m-size) Farley-Buneman (FB) waves in or near the vertical direction in the equatorial electrojet. The presence of these ‘two-step’ FB waves facilitates the study of their properties as a function of altitude and driving conditions in the equatorial E region. A study of their Doppler shift using a VHF radar at Pohnpei, during an event when the echo strength went through exceptionally strong power returns for a short time, has revealed that: 1) the Doppler shift of the vertical echoes increases with power; 2) the largest Doppler shift values increase with decreasing altitude; 3) the Doppler shifts as a whole are stronger off the zenith than at the zenith. In addition, during the same event we have observed that the up-down and east-west power asymmetries became less pronounced as the power increased and would actually be reversed at the higher altitudes under these strongly excited conditions. Our interpretation of the observations is that: 1) the aspect angle of the FB structures was so small that non-isothermal processes played an important role in determining the saturation (threshold) speed. Theoretical calculations have shown that non-isothermal effects become more important at small aspect angles at lower altitudes, which can increase the threshold speed by as much as 50%, in agreement with the observations; 2) The fact that the Type-1 speeds are often smaller than the observed non-isothermal threshold indicates that they are either observed somewhat outside the ‘instability cone’ (our preferred explanation) or that they have a larger aspect angle than their faster counterpart; 3) The east-west and vertical power asymmetries are due to an asymmetry in the nonlinear evolution of gradient-drift structures, which favours larger amplitudes for depletions (holes) than for enhancements (blobs). The larger amplitude structures are associated with a larger rotation of the total electric field away from the vertical. However, if the amplitude of the density structures increases too much, the net electric field inside the structures also weakens, which leads to a reversal of the power asymmetries under such circumstances.



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Intense Stormtime Equatorial Electric Fields and Evidence for Anomalous Resistivity in the Electrojet

R. R. Ilma1, M. C. Kelley1 and J. L. Chau2

1: School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA ([email protected]) 2: Jicamarca Radio Observatory, Geophysical Institute of Peru, Lima, Peru

In November 2004, a severe disturbance in the interplanetary electric field led to a magnetic superstorm. The Jicamarca radar registered unusually strong vertical drifts (±120m/s) due to the highest magnitude penetrating electric field ever recorded. These large and variable drifts were highly correlated with the interplanetary magnetic and electric fields, creating a double F layer on the dayside and affecting the development of a convective equatorial ionospheric storm that night. Additionally, the equatorial electrojet (EEJ) was driven at the highest value of the zonal electric field component ever registered. The curiosity is that the current in the electrojet did not register a corresponding increase suggesting a form of anomalous resistivity. We present a possible mechanism to explain them.

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The effect of dust particles on the growth time and amplitude of type I and type II irregularities in the E-region

P. Muralikrishna1 and V. H. Kulkarni2

1: Instituto Nacional de Pesquisas Espaciais, S. J. Campos-SP, Brazil ([email protected]) 2: Mumbai, Índia.

Two stream and cross-field instability mechanisms operating in the collisional plasma in the E-region of the ionosphere are affected by the ambient dust particles. It is assumed that only electrons are magnetized in this height region. The production of ions and electrons and their loss due to attachment on dust particles are included in the analysis. In the low-density region between E and F layers, density irregularities, ionization and other features are known to be associated with meteors. The extremely low effective conductivity of the mesospheric dusty plasma can explain the existence of vertical electric fields observed in the lower mesosphere, in the vicinity of noctiluscent clouds and polar mesospheric solar summer echoes. We strongly suggest that the observation of persistence of Leonid meteor trails is due to a reduction in the wave amplitudes and their dependent diffusion rate by the process. This reduction is possible due to the presence of sub-micron size dust particles introduced mainly by meteors. We show that due to attachment of both ions and electrons on dusts the two stream instability requires drift velocities much higher than ion acoustic velocities for its onset. The wave growth rate and the amplitude of both Type I and Type II irregularities are modified by the meteoric dust particles by modifying the collision parameters as well as by creating electron bite outs. These studies are important to assess the generation of density irregularities and associated effects, especially during the period of intense meteor showers.



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Aspect angle measurements of irregularities in the equatorial E region above Jicamarca

F. Lu1, D. T. Farley2, and W. E. Swartz2

1: Augsburg College, Minneapolis, Minnesota 2: Cornell University, Ithaca, New York, USA ([email protected])

We have revisited, refined, and extended the 50 MHz radar aspect angle measurements made at the Jicamarca Radio Observatory in Peru by Kudeki and Farley in 1985, taking advantage of the now considerably upgraded facilities of the Observatory. We study here (1) both type 2 and type 1 echoes in the electrojet region, (2) early evening echoes from somewhat above the electrojet, and (3) daytime “150 km” echoes in the ~145 to 170 km altitude region. Our electrojet data (a) confirm the results of the earlier study for weakly driven type 2 conditions, namely that the aspect angle θrms(ω) = <(θ-<θ>ω)2>½ (where <> implies expected value or a time average and θ is measured from perpendicular to B), decreases from about 0.3º at 99 km to slightly less than 0.2º at 108 km; and (b) provide much more information about the aspect angles of type 1 echoes and the apparent nonlinear interaction between type 1 waves and slower waves. Type 1 waves, with phase velocities near the ion-acoustic velocity, have aspect angles decreasing from about 0.15º near 104 km to about 0.10º near 110 km. Furthermore, there is strong evidence that horizontally travelling type 1 waves can nonlinearly couple to slow, vertically travelling waves with aspect angles sometimes larger than 0.5º. These waves, which we will call type 1C (for coupled), are not unstable gradient-drift waves, even though the phase velocities are similar. In the early evening we often observe echoes in the 125-135 km region with aspect angles of 0.05º or even less. During the daytime the relatively weak “150 km” echoes have even smaller aspect angles that are about at the limit of our measurement resolution. At the end of the talk we discuss ideas that may advance our understanding of the nonlinear aspects of electrojet irregularities, particularly of type 1 waves.

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Counter electrojet features in the Brazilian sector: Simultaneous observation on radar, digital sounder and magnetometers data

C. M. Denardini1, M. A. Abdu1, H. C. Aveiro1, P. D. S. C. Almeida1, L. C. A. Resende1,2, Ê. P. A. Olívio1, J. H. A. Sobral1, and C. M. Wrasse3

1: Inst. Nacional de Pesquisas Espaciais, S. J. Campos, SP, Brasil ([email protected]) 2: ETEP Faculdades, S. J. Campos, SP, Brasil 3: IP&D, Universidade do Vale do Paraíba, S. J. Campos, SP, Brasil

Counter electrojet events have been detected in Brazil with the RESCO radar and two set of fluxgate magnetometer. RESCO radar is a 50 MHz backscatter coherent radar installed in 1998 at São Luís (SLZ, 2.33° S, 44.60° W), an equatorial site. The magnetometers are fluxgate-type installed at SLZ and Eusébio (EUS, 03.89° S, 38.44º W). In addition, electron density profile is routinely monitored at the radar site by a digital sounder. Several cases of westward morning electrojet and its inversion to the normal eastward equatorial electrojet (EEJ) have been observed as seen in magnetometers signatures of the EEJ strength obtained from the difference between the horizontal component of magnetic field at SLZ station and the same component at the low latitude magnetic station, EUS. Moreover, some cases of counter electrojet (CEJ) have been detected. In the present work, we show some characteristics of normal EEJ inversion in the morning hours and CEJ events observed in Brazil with the magnetometers as well as



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with the RESCO radar. Electron density profiles are used to infer the presence of sporadic layers and to provide the current status of the ionospheric ionizations level. The spectral characteristics and power intensity of the backscattered echoes are examined.

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Irregularities in the low- and mid-latitude E region: A historical perspective

Roland T. Tsunoda

SRI International, Menlo Park, California, USA ([email protected])

Recent investigations of E region irregularities in the low- and mid-latitude E region have focused on the electrodynamics associated with larger-scale structures, in particular, wind shear and sporadic E in the nighttime ionosphere. Small-scale irregularities responsible for radar backscatter appear explainable in terms of the gradient-drift instability, operating locally without effects of field line mapping. A brief review will be presented that outlines the historical flow of research, the findings, and the status of our understanding. In particular, earlier findings are revisited to determine whether interpretation, at the time of discovery, remains reasonable, or whether a new interpretation emerges when viewed in light of current thinking. Topics of interest include Hall polarization, a sporadic-E layer instability, the effects of electrical coupling between the E and F regions, and neutral dynamics and the Kelvin-Helmholtz instability.

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Quasi-periodic variation of the sporadic E layer reflection

A. Bourdillon1, P. Dorey2 and S. Saillant2

1: IETR, Université de Rennes 1, Rennes, France ([email protected]) 2: DEMR, Onéra, Palaiseau, France

Sometimes, the sporadic E layer (Es) is described as patchy, meaning that on these occasions the radio waves are either penetrating the layer or reflected by a high electron density patch. In July 2006, an unusual one hop propagation mode 1Es has been observed at midlatitude using the Nostradamus HF radar. The event lasted about 40 minutes and during this time interval the Es reflection had a patchy character but with an unusual quasi-periodic behaviour. Most of the time the quasi-period was close to 10 sec but for a few seconds, a shorter 2 sec quasi-periodic reflection was also observed, superimposed on the slower 10 sec reflection. A simple model based on a periodic variation of the Es critical frequency is developed to explain the characteristics of these observations. The simulations agree well with our observations if the FoEs variation is sufficiently large but for now it is not clear how such a variation could be created.

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Some intriguing features of QP echoes revealed by Gadanki radar observations and a mechanism that explains them

N. Venkateswara Rao1, A. K. Patra1, and S. V. B. Rao2

1: National Atmospheric Research Laboratory, Gadanki, India ([email protected]) 2: Department of Physics, S. V. University, Tirupati, India

Quasi-Periodic (QP) occurrence of E-region echoes has been a subject of intense scientific investigation since they indicate the potential role of neutral dynamics in the manifestation of plasma irregularities.



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Discovered in the mid-latitudes, they are now known to occur in the low latitudes also. Surprisingly, they do not occur at the equatorial electrojet, where strong current and irregularities are known to occur.

In this paper we study the low latitude QP echoes based on 147 nights of observations made in all seasons using the Gadanki MST radar (dip latitude 6.5o N). These observations have uncovered many intriguing features of low latitude QP echoes that were not known based on the limited observations reported earlier. Some of the intriguing features of QP echoes revealed by the Gadanki radar are: (1) structures with dominant periods of 2-3 minutes, which alone occurs for 30 % of the time, (2) durations of QP echoing events are commonly 2-5 hours and occasionally 8 hours, (3) QP echoes are often found embedded in descending echoing regions with high altitude QP echoes occurring during 21-00 LT, (4) QP striations with similar periods are found at distinctly different heights, (5) QP echoes are found to occur maximum in the post midnight hours, (6) QP echo occurrence shows a strong seasonal dependence with maximum being in summer and minimum being in winter, and (7) remarkably higher occurrence rate of QP echoes at Gadanki (50 % of the time) than that of mid-latitudes.

Interestingly, the seasonal variations of QP echo occurrence are similar to those of sporadic-E, tidal wind, and gravity wave activities. Also the local time and height variations of the high altitude echoes (the descending layers) including the QP echoes embedded in it are found to agree very well with those of Es.

We propose a mechanism involving the zonal component of tidal and gravity wave winds to account for the above observations. In this mechanism, shears associated with such winds are shown to form enhanced plasma structures, like plasma blobs, which when polarized become unstable to form irregularities in a quasi-spatial sense. These quasi-spatial irregularities when drift through the radar beam manifest as QP echoes that we observe. The above mechanism also includes the KHI perspective. Considering that the dip angle over Gadanki is 13o, we have examined the efficiency of wind shear forming enhanced plasma structures based on realistic winds. Both tidal and gravity wave winds have been considered to reproduce the common descending echoing region as well as QP enhanced plasma structures. Intriguing features of the low latitude QP echoes and the proposed mechanism that is capable of accounting for these observations will be presented and discussed in detail.

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Intriguing details of 150-km radar echoes revealed by off-equatorial observations made from Gadanki and Kototabang

A K Patra1, N Venkateswara Rao1, T. Yokoyama2,3, Y. Otsuka2, and M Yamamoto4

1: National Atmospheric Research Laboratory, Gadanki, India ([email protected]) 2: Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa, Japan 3: Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA 4: Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan

150-km echoes have been puzzling since they were discovered at Jicamarca in 1960’s. Originally thought to be confined to the close vicinity of the magnetic equator, they have been frequently observed at 6.5o N magnetic latitude using the Gadanki radar in India. More recently, they have been detected successfully at 11o S magnetic latitude using a relatively low power Equatorial Atmosphere Radar (EAR) in Indonesia. The echoing morphology at both the off-equatorial locations have shown a necklace pattern with spectral characteristics similar to those observed at the equatorial locations. Further, the Doppler velocities are found to be consistent with the daytime eastward and upward electric field, providing a tool to study low latitude electrodynamics. Interestingly, Gadanki observations showed no remarkable seasonal variation in their occurrence, which is quite similar to those of Jicamarca. Thus these observations contrast those of



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Pohnpei, where it was shown that it is mainly a summertime phenomenon. Recent observations made using the EAR in summer and winter show nearly similar features, indicating the absence of strong seasonal contrast over Kototabang also. Thus the observations at both Gadanki and Kototabang seem to be similar in terms of seasonal variations, which are important in regard to a generation mechanism that is linked to low latitude Es. Interestingly, in contrast to the 150-km occurrence, the seasonal variations of E region FAI at Gadanki and Es activity at a nearby location both show strong seasonal variations-dominance in local summer.

EAR observations also show east-west power asymmetry but different from those of Pohnpei. A detailed investigation on the angular distribution of these echoes show that it follows an elliptical pattern whose major axis is in the southeast direction with its axis oriented at ~6o with the magnetic south. These results clearly indicate that the irregularities responsible for the 150-km echoes have direction dependent growth, an important aspect to be considered for the generation mechanism. But the puzzling aspect is that the direction of maximum occurrence appears to be different for different locations as revealed from Pohnpei and Kototabang observations.

Finally, a comparison of signal detectabilities at Gadanki and Kototabang with those of Jicamarca clearly suggests that no noticeable latitudinal dependence in echo strength exists at least up to 11o latitude, indicating the possibility of their existence at mid-latitudes. Experiments with the MU radar are underway to test this hypothesis. These results are expected to be known by the time of symposium.

Intriguing aspects of off-equatorial observations from Gadanki and Kototabang and hopefully the MU radar results will be presented and discussed to address the issues related to daytime 150-km echoing phenomenon.

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150 km echoes: Recent results from the Pacific sector

R. T. Tsunoda1 and W. L. Ecklund2

1: SRI International, Menlo Park, California, USA ([email protected]) 2: Boulder, Colorado, USA

The source mechanism for the so-called 150 km (or F1) echoes continues to elude researchers, since their discovery more than 40 years ago. Moreover, our understanding of the underlying processes that are likely to be involved seems to become less clear as new results are obtained. Questions have now been raised regarding their ubiquity or seasonal dependence, the nature of the necklace-like pattern and their apparent lack of dependence on the inclination of the geomagnetic field, and some of the echo characteristics. In this paper, we will summarize the characteristics of these F1 echoes, which have been obtained by two radars in the Pacific sector, one at Pohnpei and the other at Christmas Island. Some of unique findings include a seasonal dependence, a viewing aspect sensitivity, and the sheetlike distribution of echoes within the radar scattering volume. These results are discussed in terms of the possible underlying physics.



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The formation, evolution and radar reflection from meteor trail plasma irregularities

Lars Dyrud1, Meers Oppenheim2 E. Kudeki3, Sigrid Close4, and Diego Janches5

1: Center for Remote Sensing Inc., Fairfax, VA, USA ([email protected]) 2: Boston University, Boston, MA, USA 3: University of Illinois at Urbana-Champaign, Illinois, USA 4: Las Alamos National Laboratory, Las Alamos, NM, USA 5: CoRA/NWRA, Boulder, CO, USA

We have understood for over a decade that radars pointed perpendicular to the Earth’s geomagnetic field are capable of observing a unique variety of echoes from meteor trails. Such echoes have been termed anomalous echoes, range-spread trails, and we have adopted non-specular echoes to differentiate them from their specular counterparts which are traditionally observed with meteor radars. The Earth is continuously bombarded by meteoroids, and because most of this flux is comprised of very small meteors of the order of 1 microgram, they are either undetected, or measured only by radars. Significant uncertainties in this flux, and a desire to better understand E-region plasma physics has motivated an effort to understand and explain these non-specular trail observations. We have used plasma simulation and theory to demonstrate that meteor trails are unstable to the growth of a variety of gradient-drift Farley-Buneman (GDFB) waves that become turbulent and generate large B-field aligned irregularities (FAI). This talk shall focus on describing meteor trail instability theory, together with the inclusion of this theory in a model of meteor trail evolution, which is used to produce simulated radar observations. We shall present comparisons between these simulated radar observations and non-specular trail observations to demonstrate the capacity of this model to explain observed features, and eventually extract information about the observed meteors and the atmosphere and ionosphere that they are generated in.

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Multi-static common volume radar observations of meteor echoes at Jicamarca

Akshay Malhotra1, John D. Mathews1, and Julio Urbina1

1: The Pennsylvania State University, University Park, PA, USA ([email protected])

The first ever multi-static, common-volume radar observations were carried out at the Jicamarca Radio Observatory (JRO) in June 2007: A second antenna array, of similar sensitivity to a single JRO receive module, was constructed and operated at Carapongo, ~5.27 kilometers geomagnetically south of JRO 50 MHz radar, for this purpose. More details regarding the construction and geometry of this multi-static system are provided in Malhotra et al. [Geophys.Res.Lett., 34, L24103, doi:10.1029/2007GL032104]. These interferometric observations verify and advance the hypothesis put forward by Malhotra et al. [ J. Geophys. Res., 112, A12303, doi:10.1029/2007JA012576] i.e. if two identical radars are placed close to each other and observing a common volume, a RSTE (Range-Spread Trail-Echo) occurring at the k ⊥ B region of one of the radars might be seen as a long duration event from that radar (provided the radar has sufficient sensitivity) and a short duration event from the other radar, thus lending further insights into the aspect sensitivity of meteor trails. The physical structure of the trails combined with their aspect sensitivity raises some interesting questions regarding the plasma processes driving the formation of these



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trails, strongly suggesting a different formation mechanism for the lower altitude trails (below ~ 95 km) compared to the higher altitude trails.

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Meteor observations as a method of determining atmospheric properties

E. Bass1, M. Oppenheim1, G. Sugar1, and J. Chau2

1: Boston University, Massachusetts, USA ([email protected]) 2: Jicamarca Radio Observatory, Lima, Peru

High-power, large-aperture (HPLA) radars such as the Jicamarca Radio Observatory (JRO) in Peru provide accurate measurements of meteoroid velocities, trajectories and signal strengths. For many years, researchers have inferred meteoroid mass from the deceleration and, more recently, from the signal strength. The calculation of mass from deceleration is highly sensitive to atmospheric density, which is not often known with great accuracy. By fitting the deceleration rates of many head echoes to a differential meteor ablation model within a short time period, we find a best fit for the density and scale height of the neutral atmosphere. Small deviations in neutral density cause the fit between the model and data to lose accuracy rapidly. In this poster, we demonstrate how one applies this approach, its limitations and its usefulness as a method of remotely sensing neutral atmospheric properties.

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Plasma waves induced by meteors in equatorial E region - rocket borne results of Leonid meteor shower of Nov. 1999.

S.P. Gupta

Physical Research Laboratory, Ahmedabad 380 009, India ([email protected])

The meteor particles get deposited continuously in the earth’s lower ionosphere (80 km-140 km) both in the form of ions due to ablation of meteoric particles as well as due to sputtering of micrometeorites. The meteoric particles enter the earth’s atmosphere with a veolocity ranging from 12 km/sec to 72 km/sec. These meteor particles can be sporadic meteors or meteors associated with meteor showers. The meteor showers are debris of comets with which they are associated. The Leonid shower is associated with comet Tempel/Tuttle. The meteor showers are named according to the constellation they appear to come from, called radiant. The Leonid shower appears to come from constellation Leo. The Leonid shower occurs every year on 18 Nov. with meteor particle Zenith Hourly rate (Z.H.R.) about five. However, once in 33 years when Comet Tempel/Tuttle comes within the inner solar system, the Z.H.R. can be 10000/hr or even more. This event happened in Nov. 1998 and Nov. 1999: We conducted rocket experiments on 18 Nov. 1999 and 20 Nov. 1999 from Indian Rocket launch range SHAR (14°N, 80°E, Mag. Lat. 6.0N). On 18 Nov. rocket was launched on 0725 hrs IST. At this time the meteor activity was maximum (2 UT ≡ 730 IST). The constellation Leo was overhead over middle east at this time when Zenith hourly rate was 4000/hr. Over India the ZHR can be about 3000/hr. The second rocket was launched on 20 Nov. when the activity was reduced to one third compared to 18 Nov. The ground based study was done by ionosonde and MST radar (53 MHz) situated at SHAR and at Gadanki (14°N, 79° E) respectively.

The electron density and electron density irregularities were measured by high frequency response Langmuir probe in altitude region 70 km to 140 km. Following were the important results:



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The plasma irregularities in scale size of half meter were observed in 100 km to 120 km region with a peak amplitude of about 4% at 105 km. On 20 Nov. the irregularities were observed from 100 km to 107 km. But the peak altitude was same i.e. at 105 km.

The electron density profile on 18 Nov. shows some structures while electron density profile of 20 Nov. was smooth.

Three meter scale size irregularities were not seen in the altitude region of 100-120 km on both the days.

The ambient electric field does not play important role in the generation of sub-meter scale size irregularities, as the second day was a counter electroject event.

The irregularities move in east-west direction. There is evidence that they move with ion acoustic velocity.

One year earlier, on 18 Nov. 1998, sub-meter scale size irregularities were observed by radars at ALTAIR (9°N, 167°E, Mag. Lat. 5°N) when the ZHR of meteor was nearly same as it was on 18 Nov. 1999 over Indian zone. Also the local time was the same. The ALTAIR observations were carried out by American scientists.

We will compare these results with theory.


Session S6: F-region plasma irregularities: causes and effects

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Initiation of equatorial Spread F

E. Kudeki1, A. Akgiray1, M. Milla1, J. L. Chau2, and D. L. Hysell3

1: Department of Electrical and Computer Engineering, University of Illinois at Urbana([email protected]) 2: Radio Observatorio Jicamarca, Lima, Peru 3: Cornell University, Ithaca, New York, USA

We present experimental evidence and modeling results which suggest that eastward thermospheric wind may be the primary controlling factor of equatorial spread-Finitiation in the post-sunset ionosphere. Eastward wind driven Pedersen currents should be able to polarize F-region density perturbations with westward tilting wavefronts into rapidly growing modes to trigger the formation of spread-F bubbles. The described process, which depends on differential motion between the neutrals and bottomside F-region plasma, can be so rapid that seeding requirements of spread-F initiation by external factors such as gravity waves may not be essential.

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Equatorial spread F irregularity development conditions as diagnosed from conjugate point observations by digisondes and all-sky imagers in Brazil.

M. A. Abdu1 , I. S. Batista1, B. W. Reinisch2 , J. R. de Souza1 , J. H. A. Sobral1, T. R. Pedersen3 A. F. Medeiros4 , N. J. Schuch5, and E. R. de Paula1.

1: Instituto Nacional de Pesquisas Espaciais, São José dos Campos, SP, Brasil. ([email protected]) 2: Center for Atmospheric Research, University of Massachusetts, Lowell, MA, USA 3: Air Force Research Laboratory, AFRL/VSBXI, 29 Randolph Rd, Hanscom AFB, MA 01731-3010, USA. 4: Universidade Federal de Campina Grande, PB, Brasil. 5: Centro Regional Sul de Pesquisas Espaciais, INPE, Santa Maria, RS, Brasil.

A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October - December 2002 period in Brazil, with the objective to investigate the equatorial spread F/plasma bubble irregularity (ESF) generation and development conditions in terms of the electrodynamical state of the ambient ionosphere along the magnetic flux tubes in which they occur. A network of instruments including Digisondes, optical imagers, and GPS receivers, were deployed at magnetic conjugate and dip equatorial locations, in a geometry that permitted field line mapping of the conjugate E layers to dip equatorial F layer bottom side. This paper address ESF/ plasma bubble initiation by large scale wave structures, and discusses the competing influences of the evening vertical plasma drift in favoring the ESF development versus that of the trans-equatorial winds in suppressing its growth. A perspective on the causes of the ESF day-to-day variability is also presented.

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On the role of large-scale wave structure in the initiation of equatorial plasma bubbles

Roland T. Tsunoda

SRI International, Menlo Park, California, USA ([email protected])



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We examine existing experimental evidence to evaluate whether large-scale wave structure (LSWS) is playing an important role in the initiation of equatorial plasma bubbles. Until recently, a general impression was that the gravitationally driven interchange (Rayleigh-Taylor) instability is the primary source mechanism for plasma bubbles, but that a seed perturbation is needed because its growth rate seems small. Various seeding processes have been suggested, which include atmospheric gravity waves, a collisional-shear instability, and E-region polarization processes. More recently, another form of the interchange instability, driven by an eastward neutral wind, has been proposed [Kudeki et al., 2007], which appears to have a growth rate much larger than that of the Rayleigh-Taylor instability. Given the vigor of the new instability, there is now question as to whether a seeding process is necessary or important, and what role seeding plays, if any. Various datasets will be described and compared to the predictions of the newly discovered process.

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Relation between ESF occurrence rate and prereversal plasma drift velocity

C. Stolle1, H. Lühr1, B. Fejer2, and J. Jensen2

1: Geoforschungszentrum Potsdam, Germany ([email protected]) 2: Center for Atmopsheric and Space Science, Utah State University, UMC 4405, Logan, UT 84322-4405, USA

It is widly accepted that the occurrence rate of the post-sunset equatorial F region plasma instabilities, often named Equatorial Spread-F (ESF), show a typical seasonal/longitudinal (s/l) distribution. Supporting global observations are now possible with recent satellite measurements of ESF involved electron density depletions (e.g., on board ROCSAT-1 or DMSP) or of magnetic field enhancements inside ESF due to the diamagnetic effect (on board CHAMP).

Different mechanisms have been proposed to explain the observed ESF occurrence rate structure. There are electromagnetic conditions of the ionosphere, such as the alignement of the geomagnetic field with the sunset terminator, the strength of the ionisation anomaly, and the strength of the vertical upward plasma drift during the Pre-Reversal Enhancement (PRE). The latter one enhances the ESF growth rate in two ways: it creates a force parallel to the density gradient and antiparallel to gravity, and it pushes the ionosphere to higher altitudes, where the ion-neutral collision frequency is decreased.

This paper presents the comparison of two independent continuous data sets between 2001 and 2004; the CHAMP ESF occurrence rate and the vertical E×B plasma drift velocity derived from ROCSAT-1 observations. Special advantage lies in the full local time availability of drift observations which allow the investigation of the PRE peak value and the integrated effect of the entire PRE period. We find excellent agreement in the s/l distribution of ESF occurrence rate and the plasma drift with corellation coefficients above 0.8 in all seasons. These results emphasises the PRE E×B plasma drift velocity as the dominant contributor in ESF initiation. Going one step further, we investigate the local time of ESF occurrence and compare these findings with the change in local time of the PRE depending on season and longitude.

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Longitude dependent electrodynamic effects on equatorial F-region plasma irregularities

B. G. Fejer

Center for Atmospheric and Space Sciences, Utah State University, 4405 Old Main Hill, Logan, UT 84322-4405 ([email protected])



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Satellite and ground-based observations have shown that the occurrence of equatorial nighttime F-region plasma irregularities are strongly season and longitude dependent. The generation and evolution of these are strongly affected by the evening equatorial vertical plasma drifts during both geomagnetically quiet and disturbed times but they can also be affected by other processes. In this talk, we review the studies of the longitudinal variations of these irregularities and the physical processes proposed to explain them. Then, we discuss the possible roles of season and longitude dependent vertical and zonal plasma drifts on the generation of these irregularities during geomagnetically quiet and disturbed times.

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VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia

Y. Otsuka1, T. Ogawa1, and Effendy2

1: Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa, Japan ([email protected]) 2: National Institute for Aeronautics and Space, Bandung, Indonesia

We report continuous observations of the nighttime F-region field-aligned irregularities (FAIs) observed with a VHF Doppler radar at Kototabang (0.20oS, 100.32oE; dip latitude 10.4oS), Indonesia. Operating frequency and peak power of this radar is 30.8 MHz and 20 kW, respectively. Five beams were allocated between +/-54o around geographic south (126o-234o). From the continuous observation from February 2006 to February 2008, we found that FAIs appeared frequently at pre-midnight between March and May and at post-midnight between May and August. The pre-midnight FAIs coincided well with GPS scintillation observed at the same site. Seasonal and local time variations of the pre-midnight FAI occurrence are consistent with those of equatorial plasma bubbles reported in previous studies. These results indicate that the pre-midnight FAIs could be associated with the equatorial plasma bubbles. On the other hand, seasonal and local time variations of the post-midnight FAIs were inconsistent with those of the plasma bubbles. The features of the post-midnight FAIs can be summarized as follows: (1) The post-midnight FAIs are not accompanied by GPS scintillations. (2) Most of the post-midnight FAI regions do not show propagation, but some of them propagate westward. (3) Echo intensity of the post-midnight FAIs was weaker than that of the pre-midnight FAIs. These features are similar to those of the FAI echoes that have been observed at mid-latitude. However, mechanism generating the post-midnight FAIs is still unknown.

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Three-dimensional simulation of equatorial Spread-F with meridional winds

J. Krall1, J. D. Huba1 and G. Joyce2

1: Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5346 ([email protected]) 2: Icarus Research, Inc., P O Box 30780, Bethesda, MD 20824-0780

A new three-dimensional simulation code[1] is used to examine the effect of meridional winds on the growth, and possible suppression [2] of equatorial spread-F. The simulations are initiated using the SAMI2[3] code and use a SAMI3-like dipole field geometry that extends up to 1600 km at the equator and down to and altitude of 85 km, but only a few degrees in longitude. Both periodic and non-periodic boundary conditions are considered in the longitudinal direction. The full SAMI3 ionosphere equations are included, providing ion dynamics both along and across the field. The potential is solved in two dimensions (longitude and L-shell) under a field-line equipotential approximation.



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References:

[1] Huba, J. D., G. Joyce, and M. Swisdak, 2007AGUFMSA21B..04H

[2] Zalesak, S. T., S. L. Ossakow, and P. K. Chaturvedi, JGR, 87, 151-166, 1982

[3] Huba, J.D., G. Joyce, and J.A. Fedder, JGR, 105, 23,035, 2000

Work supported by ONR

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DEMETER observations of highly structured plasma density and associated ELF electric field and magnetic field irregularities at middle and low latitudes

R. Pfaff1, C. Liebrecht1, J.-J. Berthelier2, M. Parrot3, and J.-P. Lebreton4

1: NASA Goddard Space Flight Center, Greenbelt, MD, USA ([email protected]) 2: CETP, St. Maur, France 3: LPCE, Orleans, France 4: ESA, Noordwijk, Netherlands

Since its launch in June, 2004, the DEMETER spacecraft has gathered near-continuous measurements of numerous plasma parameters near 720 km altitude between +/- 65 degree invariant latitude in a sun-synchronous orbit providing local time coverage of ~ 10:30h/22:30h. At low latitudes, the instruments commonly encounter highly structured plasma density regions at night that are equatorward of the Appleton anomaly region (magnetic latitudes < 15-20 degrees) and which are generally associated with equatorial spread-F depleted flux tubes. During severe geomagnetic storms, however, the spacecraft detects much broader regions of nightside plasma density structures that extend to higher latitudes, in some instances from the equator to the sub-auroral regions. These structures resemble spread-F plasma depletions although sometimes, plasma density enhancement structures are present as well. The large scale plasma structures with scale lengths along the spacecraft trajectory of 100's of km display clear, associated electric field irregularities with broad spectra that typically span from less than 1 Hz to ~ 500 Hz (roughly 10 km to 20 m). In addition to the electric field irregularities, in some cases, ELF magnetic field irregularities are also observed. Such AC magnetic signatures are typically observed on the walls of the plasma density structures and appear to be related to finely-structured spatial currents and/or Alfven waves. We analyze the irregularities observed in the electric field and magnetic field data in order to elucidate their generation mechanism(s), using high time resolution, burst memory waveforms when available. The mid-latitude irregularities are compared with those associated with equatorial spread-F as well as with the intense irregularities associated with the trough region that are observed at sub-auroral latitudes during geomagnetic storm periods.

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Topside plasma bubbles, seen as He+ density depletions, and thermosphere meridional wind influence

L. Sidorova

Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation (IZMIRAN), Troitsk, Moscow region, Russia ([email protected])

The present study deals with the evaluation of the possible contribution of the thermosphere meridional/transequatorial winds in the diurnal occurrence probability of the equatorial and low-latitudinal



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plasma bubbles. It is suggested, that the plasma bubbles, produced by Rayleigh-Taylor instability at the bottomside of ionosphere and transported up by buoyancy to the topside ionosphere and plasmasphere, could be strong affected by meridional (poleward) wind during a generation due to inhibiting the growth of Reyleigh-Taylor instability and flux tube integrated conductivity. He+ density depletions, considered as originating from equatorial plasma bubbles phenomena, or as possible fossil bubble signatures (Sidorova, Adv. Space Res., 2004, 2007), were involved in this study. These plasma bubbles seen as He+ density depletions are usually observed during a high solar activity at the topside ionosphere altitudes deeply inside the plasmasphere (L~1.3-3). Their diurnal occurrence probability, obtained from ISS-b satellite data (1978-79) for the different months and averaged for the periods around the solstices and equinoxes, was compared with the model velocity variations of the meridional thermosphere wind. The best amplitude correlation was found in the longitudinal region of 270-360° (Brazilian, Atlantic regions), where the declination angle of the magnetic meridional component of the thermosphere wind is near 20΅ . The wind model calculation, made by Maruyama (JGR, 1996), was used for analyses. It was obtained that the topside plasma bubbles seen as He+ density depletions are strong enough affected by meridional wind. The modulation effect has a seasonal dependence. The best correlation coefficient was found for equinox season (R=0.87). Plasma bubble distribution as function of latitude-longitude, their longitudinal statistics and the map of the magnetic declination, calculated from IGRF 1975, were involved for further analyses. It was concluded that the significant modulation effect is determined by season and declination angle of the earth magnetic field in the equatorial region.

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New aspects of mid-latitude plasma plumes revealed by radio and optical observations

Shoichiro Fukao and Mamoru Yamamoto

Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Kyoto, Japan ([email protected], [email protected])

The mid-latitude ionosphere sometimes shows rapid and turbulent upwelling during sunspot minimum condition, which is called plasma plume after its shape. The plume is characterized by intense coherent radar echoes from 3-m scale field-aligned irregularities (FAIs). Simultaneous coherent and incoherent scatter observations by the MU radar indicates that the FAIs are generated on the bottom side of the F region. The traveling ionospheric disturbances (TIDs) deeply modulate the bottom side of the ionosphere, which may vary the 630 nm band airglow luminosity. The FAIs are detected in the nights when TIDs are intense in amplitude and ionosphere is uplifted. The FAIs form band-like structures that travel to the southwest. Their wavefront and travelling speed are generally consistent with those of the TIDs that are simultaneously detected by the TEC observation. Also, TIDs are associated with perturbation of electric filed in the ionosphere (A. Saito et al., 1995, 1998; Shiokawa et al., 2003). These results suggest that the horizontal gradient of the electric conductivity associated by TIDs and the vertical gradient of the conductivity on the bottom side of the F region ionosphere generates the 3-m scale FAIs through the gradient-drift instability process (A. Saito et al., 2002).

The possible relationship between the F-region and E-region FAIs was suggested early by Kelley and Fukao (1991). S. Saito et al. (2007) shows that band structures of E-region irregularities aligned northwest to southwest drift to the southwest, and their wavefront and propagation direction are the same as those of medium-scale TIDs (MSTIDs) in the F region. Yamamoto et al. (2007) simultaneously observed FAIs by radar imaging technique along the same geomagnetic field lines in the F region with the



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MU radar and in the E region with a portable coherent radar (F- and E-Region Ionospheric Coupling Study or FERIX campaigns). While the northwest-southeast wavefront with small substructures existed in the F region, quite similar structure was formed in the E region too, and both propagate to the southwest or west. The substructure as small as a few tens of km in the F region propagated to the northwest with various Doppler speeds. This indicates that the F and E regions in the nighttime mid-latitude ionosphere must be considered electrodynamically as a coupled system.

It has been recently found by airglow imager observations at the conjugate locations at mid-latitudes that MSTIDs show an excellent conjugacy with identical structures even to smallest scales between both hemispheres (Otsuka et al., 2004). This may suggest that the E- and F-region coupled system be considered in more global scale.

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Observations of ESF irregularities using simultaneous radar and GPS over Indian region

S. Sripathi1, S. Bose1, A. K. Patra2, T. K. Pant3, B. Kakad1 and A. Bhattacharyya1

1: Indian Institute of Geomagnetism, Navi Mumbai, India ([email protected]) 2: National Atmospheric Research Laboratory, Tirupati, India 3: Space Physics Laboratory, VSSC, Thiruvananthapuram, India

In this paper, we present observations of temporal and spatial variability of total electron content (TEC) and amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.50 N, 79.20 E, Dip latitude 6.30 N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuation in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. Interestingly, during magnetically quiet periods, we have detected plume type radar echoes during post-midnight that are not associated with L-band scintillations. Using spectral slopes and cross-correlation index of the VHF scintillation observations, we suggest that these irregularities could be ‘dead’ or ‘fossil’ bubbles which are just drifting in from west. This scenario is consistent with the observations where we observe suppression of pre-reversal enhancement (PRE) in the ionosonde observations and low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight event, when radar observed plume like structures and scintillations on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that small scale irregularities are generated through secondary waves that grow on the walls of km scale size irregularities. However the evolution of the RT instability itself does not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal.



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Optical observation of ionospheric plasma bubbles and mesospheric gravity waves

H. Takahashi1, A. F. Medeiros2, C. M. Wrasse3, M. J. Taylor4, P.-D. Pautet1, D. Gobbi1, J. Fechine2, M. A. Abdu1, I. S. Batista1, E. Paula1, J.H.A. Sobral1, D. Arruda1,

and D. Fritts5

1: Instituto Nacional de Pesquisas Espaciais, São José dos Campos, SP, Brazil. ([email protected]) 2: Universidade Federal de Campina Grande, Campina Grande, PB, Brazil 3: Universidade de Vale do Paraiba, São José dos Campos, SP, Brazil 4: Utah State University, Logan, USA 5: Colorado Research Associates, Boulder, USA.

During the SpreadFEx campaign, under NASA Living with a star(ILWS) program, carried out in the South American Magnetic Equator region from September 22 to November 8, 2005, two airglow CCD imagers, one located at Cariri (7.4S, 36.5W, Mag.9S) and the other at near Brasilia (14.8S, 47.6W, Mag.10S) were operated simultaneously and measured the equatorial plasma bubbles by the airglow OI 6300 intensity depletions. Simultaneous observation of the mesospheric OH emission wave structures made it possible to investigate relationship between the bubbles and gravity waves at around 90 km. From a total of 17 nights of observation, a good correlation of mesospheric gravity wave horizontal wavelength and ionospheric bubble inter-distance was found. On the evening of September 30, 2005, for example, comb-like bubble structures with a distance of ~130 km between them were observed. During the same period, mesospheric gravity wave with the horizontal wavelength of ~130 km was observed, suggesting possible seeding of the bubbles. Simultaneously observed ionospheric parameters (F-layer uplifting and scintillation) by ionosonde and VHF radar support the present hypothesis. Present work will therefore discuss a possible coupling mechanism between the ionosphere and mesosphere.

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Relationship between GPS ionospheric scintillation occurrence over Indonesia and equatorial atmospheric waves!

T. Ogawa1, Y. Miyoshi2, Y. Otsuka1, and T. Nakamura3!

1: Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi, Japan ([email protected]) 2: Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan 3: Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan!

Equatorial Ionospheric scintillation observations using 1.6-GHz GPS radio waves have been made at Kototabang, Indonesia (0.20oS, 100.32oE; dip lat. 10.36oS) since January 2003: Scintillations due to plasma bubbles appear between 2000 and 0100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. Scintillation index (S4) is compared with Earth's brightness temperature (Tbb) to find that the scintillation activity can be related to tropospheric disturbances to the west of Kototabang. The scintillation (plasma bubble) occurrences exhibit clear day-to-day variability. To investigate the reasons of this variability, we analyze data of S4, Tbb and lower thermospheric neutral wind over Kototabang. The results show that S4 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, maybe due to atmospheric waves from below, and that similar periods are also found in the Tbb and wind variations. Then, numerical simulations using the Kyushu University General Circulation Model are conducted to know the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) waves with periods of 2-20 days dissipate rapidly above about 125



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km, and waves with periods of 0.5-3 hours become predominant above 100 km. (2) Zonal wind above 200 km altitude are, on the whole, eastward during sunset-sunrise. (3) Zonal wind patterns due to short-period (1-4 hours) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30-1000 km, and as a whole, move eastward at about 100 m/s while changing the patterns with time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation can be seeded by AGWs with short periods of about 0.5-3 hours, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to about 120 km altitude from below.

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Stormtime convection and overshielding electric fields at the equator as observed with magnetometers and incoherent scatter radar

T. Kikuchi1,3 , K. K. Hashimoto2, Y. Tsuji1, S. Watari3, and B. Fejer4

1: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan 2: Kibi International University, Takahashi, Okayama, Japan 3: National Institute of Information and Communications Technology, Koganei, Tokyo, Japan 4: Center for Atmospheric and Space Science, Utah State University, USA

It has been known that the magnetospheric electric field penetrated to the equatorial ionosphere during geomagnetic storms, causing eastward (DP2) and westward electrojet (CEJ) superposed on the equatorial electrojet on the dayside. We analyzed several geomagnetic storms to clarify the storm phase dependence of the occurrence of the equatorial DP2 and CEJ. First, we show that the equatorial DP2 occurred simultaneously with enhancements in the polar cap potential (PCP) and auroral electrojet (AEJ). We further show mid latitude magnetic disturbances associated with the equatorial DP2 and CEJ, indicating instantaneous development of the global DP2 currents during the main phase and reversed currents during the recovery phase. It is to be noted that the DP2 current was followed by ring current development within a few minutes, which infers that the ionospheric electric field associated with the DP2 currents played a crucial role in the development of the ring current. In other words, the convection electric field was transmitted into the inner magnetosphere via the ionosphere. We then show that the equatorial DP2 remained during the whole period of the main phase. However, a latitudinal profile of the strength of the DP2 current infers concurrent development of the shielding electric field during the storm main phase. As a result, the overshielding occurred at the beginning of the storm recovery phase when the PCP decreased its magnitude because of decrease in the southward IMF. Finally, we show a storm event characterized by concurrent development of the mid latitude DP2 and equatorial CEJ that might be caused by the disturbance dynamo electric field. A question may arise on the latitudinal distribution of the disturbance dynamo electric field in comparison with the penetrated convection electric field

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Multi-year study of the altitude distribution of scintillation-causing irregularities and gradients

E. S. Miller1, J. J. Makela1, R. L. Bishop2, and P. R. Straus2

1: University of Illinois at Urbana-Champaign, Illinois, USA ([email protected],[email protected]) 2: Aerospace Corporation, USA



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Scintillation of trans-ionospheric radio signals due to irregularities and gradients in equatorial plasma bubbles has long been a practical concern for users of space-based communication and navigation systems. Until recently, most studies of equatorial scintillation were performed using space-based transmitters and ground-based receivers, making altitude measurements relatively difficult. However, the introduction of space-based receivers such as those used for GPS radio occultation allows improved vertical resolution. Images from a field-aligned narrowfield airglow imager extruded along the geomagnetic field provide a three-dimensional map of potentially irregular regions. The intersection of these regions with occultation raypaths experiencing scintillation yields the location of the irregularities. We present the results of a several-year study using scintillation data from the COSMIC/FORMOSAT-3 (2006-2008) and IOX (2002-2004) missions and airglow images from Cerro Tololo in Chile (2006-2008) and Mt. Haleakala in Hawaii (2002-2008).

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Evolution of intermediate scale length equatorial spread F irregularities

A. Bhattacharyya and B. Kakad

Indian Institute of Geomagnetism, Navi Mumbai, India ([email protected])

Intermediate scale length (~ 100m to few km) equatorial spread F (ESF) irregularities are responsible for producing scintillations on transionospheric VHF, UHF, and L-band radio waves. Information about the pattern of evolution with time of the spatial structure of these irregularities is contained in the changing intensity scintillation pattern on the ground. Spatial scales in the ground scintillation pattern decrease as the electron density fluctuations increase, and also become shorter as the irregularity spectrum becomes shallower. The shortest scale length found in the ground scintillation pattern in the most turbulent pre-midnight phase during magnetically quiet periods, shows a tendency to increase with increasing solar flux. This may be an indication of the role played by the rate of decrease in the height of the nighttime equatorial F region after reversal of the background electric field, in determining the evolution of intermediate scale spatial structure in ESF irregularities.

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The linear dependence of L-band scintillation on electron density observed in the anomaly

J. A. Whalen

Woodville Associates, Woodville, Massachusetts, USA ([email protected])

The dependence of scintillation on electron density is determined by coinciding measurement of both parameters, and also by showing that the result is a necessary condition for the dependence of scintillation on solar flux. The measurements are from the anomaly station at Ascension Island during solar maximum on March 2003: At this site ionospheric soundings of foF2 are located near the ionospheric penetration point of the 1.5 GHz transmissions from the Marisat satellite. Although the presence of the irregularities obscures measurement by the sounders, the LT distribution of the anomaly NmF2 is so regular that it permits interpolation through the gaps in the data caused by the irregularities. As a result, values of NmF2 that coincide with the maximum S4 can be inferred. The result of 47 such coincidences is that the maximum scintillation, S4max, is a linear function of the coinciding NmF2: This dependence is also seen in LT: S4max decreases linearly with LT because NmF2 decreases linearly with LT, the latter because recombination erodes the F layer progressively with LT. In order to determine that this dependence is not



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limited to the technique of measurement used here nor to solar maximum, L-band scintillation was measured from maximum to minimum of solar cycle # 21 also at Ascension Island. Here S4 is found to increase linearly with solar flux, a relation that can exist only because scintillation increases linearly with NmF2: The dependence shown here has the consequence that, if NmF2 can be predicted, the maximum possible S4 can be predicted, examples of which are given in the following paper.

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The large TEC fluctuations near the Equatorial ionization anomaly during the equatorial spread F: observation from the GPS network over Brazil and

simulation

E. A. Kherani, E. R. de Paula, M.T.A. H. Muella, A. A. N. Campos, L.F C. de Rezende, and P.F. Smorigo

INPE-Aeronomy Division, 12.227-010 Av. dos Astronautas 1758 São José dos Campos SP, Brasil ([email protected])

To monitor the scintillation induced by ionospheric irregularities, a number of GPS receivers are deployed over Brazil. They provide the real-time distribution of scintillation activity and TEC fluctuations induced by the equatorial spread F. We has found that the TEC fluctuations is large near the equatorial ionization anomaly (EIA) as compared to the equatorial region where they are originally generated. The large TEC fluctuations near EIA region needs an explanation. To do so, we carry out the 3D numerical simulation of spread F bubble including the dynamics parallel and perpendicular to the magnetic field. The simulation shows that the large ionospheric density gradient in the equatorward boundary of EIA region is probably responsible for the observed large TEC fluctuations.

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The simultaneous rocket observation of electron density and temperature inside the equatorial spread-F bubble and their numerical simulation

F. C. de Meneses, P. Muralikrishna, and E. Alam Kherani

Instituto Nacional de Pesquisas Espaciais (INPE), Brazil ([email protected])

The ionospheric irregularities associated with spread F were first observed from the rocket flights 40 years ago. Such in-situ measurements provides useful information regarding the development of plasma depletions or bubbles and subsequent generation of small scale irregularities. These measurements have been used to obtain the power spectrum of fluctuations associated with the equatorial spread F. An equatorial station Alcantara (2.31oS, 44.4oW) in Brazil has a rocket launching facility. From this station, rocket carrying Langmuir probe was launched on 18th December 1995 at 21:17 LT. The electron density and temperature were measured from the Langmuir probe. This in-situ measurement identify the depletions along the trajectory of the rocket. Together with the density fluctuations, the temperature fluctuations are also noticed. The simultaneous measurements of density and temperature provides insight into the energetics of the spread F phenomena. The two dimensional numerical model is developed to simulate these fluctuations. The model solves the hydromagnetic equations (continuity, momentum, energy and Poisson equations) in a plane perpendicular to the terrestrial magnetic field. The measurements and numerical results are further discussed to understand the energetics of the bubble.


Poster P2: Posters for Session S5 (E-region plasma physics)

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First 3-dimensional radar interferometry observations of equatorial E region irregularities at Jicamarca

V. Belyey1, C. La Hoz1, J. Chau2, and H. Pinedo2

1: University of Tromsø, Tromsø, Norway ([email protected]) 2: Radio Observatorio Jicamarca, Lima, Peru

Radar interferometry is a relatively new remote sensing technology based on accurate cross-phase measurements of coherent radar scatter echoes received by a set of spaced antennas. A technique for image inversion developed by Hysell and Chau [2006] was successfully used for interpreting data collected during a series of experiments on interferometric observations of equatorial electrojet and equatorial spread F [e.g. Hysell and Chau, 2002, Kudeki and Sürücü, 1991] at the Jicamarca Radio Observatory. A distinction of the observations was the use of east-west baseline interferometer providing imaging in a plane transverse to geomagnetic field.

A new experimental campaign involving a newly built outlying receiving antenna was conducted in July 2007: The outlying antenna is placed at approximately 490 m (81 wavelengths) to north from main radar antenna array providing high angular resolution along the magnetic field. In total six receiving antennas, arranged in both east-west and north-south directions, were used forming 15 interferometric baselines.

We present first results of preliminary processing of the raw interferometric data collected at Jicamarca in July 2007: For the data processing a software package was developed. The package was designed within the framework of EISCAT_3D project aimed at construction of modern incoherent scatter radar in Scandinavia and financed by the EU.

References

Hysell, D. L. and J. L. Chau (2002), Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet, Annales Geophysicae, 20, 1167-1179.

Hysell, D. L. and J. L. Chau (2006), Optimal aperture synthesis radar imaging, Radio Science, 41, RS2003, doi:10.1029/2005RS003383:

Kudeki, E. and F. Sürücü (1991), Radar interferometric imaging of field-aligned plasma irregularities in the equatorial electrojet, Geophysical Research Letters, 18, 41-44.

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Perpendicular and off-perpendicular to B observations of 150-km echoes: Evidence of meridional modulation and structure

J. L. Chau1, R. F. Woodman1, and M. A. Milla2

1: Radio Observatorio Jicamarca, Instituto Geofísico del Perú, Lima ([email protected]) 2: Electrical and Computer Engineering, University of Illinois, Urbana-Champaign, IL, USA

Although discovered more than 40 years ago, there is still no physical mechanism that explains the occurrence of coherent echoes from altitudes around 150 kms (so called 150-km echoes). East-West oblique beam as well as wide beam imaging observations indicates that temporal variability of 150-km echoes (the pearls in the necklace) is not due to structuring and/or modulation in the zonal direction. Recently Chau [2004] reported the observations of echoes from 150-km region coming from off-perpendicular to B angles, implying that the aspect sensitivity (i.e., the North-South angular brightness) is



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not a narrow Gaussian as originally thought. Moreover, the spectrum of these echoes was very wide, resembling the expected incoherent spectrum at these altitudes. In this work we present the results of concurrent dual beam observations along the magnetic meridian (perpendicular to B, ~2o and ~5o off). On reception, a North-South interferometer was used for each beam, allowing for the first time, the measurement of the angle of arrival (AOA) of the 150-km signals. Our preliminary results show that the AOAs vary both in time and altitude, suggesting a meridional modulation. Moreover, the spectrum shape of the off-perpendicular to B echoes show a well defined structure that changes with time and varies with altitude. A possible scenario for the observed angles is presented. Finally, we present and discuss our attempts to characterize the enhanced wide spectra using the well-known incoherent scatter theory in this poorly understood region.

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The possible role of Inter-hemispheric-field-Aligned Current for the generation of 150-km echoes

E. Alam Kherani, E. R. de Paula, and F. Carlos de Meneses Jr.

Instituto Nacional de Pesquisais Espaciais, São José dos campos, Brazil ([email protected])

The 150-km echoes are the quasi-periodic echoes often present in the day-time equatorial ionosphere. They are routinely observed from the equatorial radars such as Jicamarca, Pohnpei and São Luís radars. Here, we present the occurrence statistics of these echoes from the São Luís radar. The radar operates at 30 MHz frequency and detects the 5 meter scale size irregularities. The five years statistics reveal the preferred occurrence of these echoes during July-August, less-preferred occurrence during December-January and least preferred occurrence during April-May/October-November. These seasonal variations are found to be very similar to the seasonal variations of inter-hemispheric-field aligned current (IHFAC) which arises due to the imbalanced sq current system across the equator.

The imbalanced current system cause the large conductivity gradient across the equator and drives the large IHFACs. Moreover, its effect is confined below 200 km in ionosphere and it is maximum at the equator. These properties together with similar seasonal variations put them as one of the possible candidate to cause the 150-km echoes. Our recent three-dimensional model of convective instability reveals the explicit contribution of parallel dynamics into the growth rate. In the absence of perpendicular (to the Earth's magnetic field) gradients and currents in the vicinity of 150 km region, the parallel contribution, thus, becomes vital. The effect of this contribution under imbalanced sq current system is investigated. This may be useful in understanding the generation mechanism of 150-km echoes.

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Unexpected rapid decrease in phase velocity of sub-meter Farley-Buneman waves with altitude∗

L.M. Kagan1, R.S. Kissack1, M.C. Kelley2, and R.A. Cuevas2

1: University of Western Ontario, London ON, Canada ([email protected]) 2: Cornell University, Ithaca NY, USA

∗ based on Kagan et al (2008), Geophys. Res. Lett., 35, in press.



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We analyze near simultaneous observations of the equatorial electrojet irregularities at frequencies of 50 and 430 MHz (corresponding to plasma irregularity scales of 3 m and 0.35 m respectively) with the JULIA radar and the newly employed Prototype Advanced Modular Incoherent Scatter Radar (AMISR-P) at the Jicamarca Radio Observatory on 12 March 2005: Both radars transmitted vertically and at both 23° and 51° off zenith to the west with JULIA and 20° off zenith to the west with AMISR-P. An unexpected and drastic drop in the phase velocity Vph of Farley-Buneman (FB) waves with increasing altitude was detected with the 430-MHz radar looking vertically. The decrease in Vph was 67 m/s and 36 m/s over 2.4 km for the FB waves moving towards and away from the radar, respectively. By contrast, the 430-MHz data from 20° west displayed little dependence on altitude. Simultaneous observations with a 50-MHz radar at 23° and 51° west also displayed little change of Vph with altitude. The altitude and velocity uncertainties for AMISR-P vertical transmissions were ±0.6 km and ±20 m/s respectively. For oblique transmissions AMISR-P received echoes from a wider altitude range 100-106 km with significantly higher altitude uncertainty of ±3.7-3.9 km averaging signal over more than 7 km. In our theoretical estimates we use computation codes based on the Kagan and St-Maurice [J. Geophys. Res., 109( A12), A12302, 2004] theory for vertical transmissions (0° flow angle) and on the Kissack et al. [Phys. Plasmas, 2008b, in press] theory for oblique transmissions at 20°-west flow angle. The procedure uses ionosphere parameters from the MSIS and the geomagnetic field from the IGRF models for the time and location of the experiment. These are used to calculate electron and ion collisional frequencies and gyro frequencies. Based on the results of Kagan and Kissack [Geophys. Res. Lett., 34, L20806, doi:10.1029/2007GL030903, 2007] in our calculations we used the corrected rate of inelastic cooling 0.007eδ = instead of 0.003 used in estimates

before, and the rate of temperature dependence on neutral frequency 0

0

e

e e

e e T

TgTν

ν⎡ ⎤∂

= ⎢ ⎥∂⎣ ⎦=

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as in our

previous work. The altitude limitation of FB wavelength imposed by the fluid theory is 0.09-0.29 m near 100-106 km (altitudes of 430-MHz echoes) and is less than 0.35 m, therefore justifying the fluid approach to the observations.

We show that electron inelastic cooling which defines gradual transition from super-adiabatic to isothermal processes at 50 MHz (used in majority of observations) and lower frequencies, becomes unimportant at higher frequencies. Our theoretical predictions match observations remarkably well. We demonstrate that the effect of a Vph drastic drop with increasing altitude is evinced at radar frequencies ≥150 MHz and requires altitude resolution <2 km to be observed. Averaging over >7 km at oblique incidence masks the effect.

Such a success of the linear theory adds further evidence for the long suspected fact that, whatever the nonlinear process generating FB waves is, it produces waves moving at their linear threshold speed.

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EEJ features based on coherent radars soundings in the Brazilian sector

C. M. Denardini1, M. A. Abdu1, J. H. A. Sobral1, C. M. Wrasse2, H. C. Aveiro1, P. D. S. C. Almeida1, L. C. A. Resende1,3, Ê. P. A. Olívio1

1: Inst. Nacional de Pesquisas Espaciais, S. J. Campos, SP, Brasil ([email protected]) 2: IP&D, Universidade do Vale do Paraíba, S. J. Campos, SP, Brasil 3: ETEP Faculdades, S. J. Campos, SP, Brasil



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In the present paper we present some features of the equatorial electrojet observed in the Brazilian sector based on the RESCO coherent radar observations. Some peculiar characteristics the equatorial electrojet are presented and discussed in terms of established concepts and theories, such as: the time of irregularities observation different, including later observations after the sunset; the center height of the scattering region and its variation as the electrojet departs from the radar site; the temporal variation of the amplitude oscillations in the echo signal. Also, the evening rising is presented in terms of its seasonal dependence, the altitudinal and time dependence of Gradient-Drift and Two Stream plasma irregularities observations are presented, and the East-West frequency and power asymmetries are shown in a comparative way to previous observations.

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Comparative In Situ measurements of plasma instabilities in the equatorial and auroral electrojets

R. Pfaff1

1: NASA Goddard Space Flight Center, Greenbelt, MD, USA ([email protected])

This presentation provides a comparison of in situ measurements of plasma instabilities gathered by rocket-borne probes in the equatorial and auroral electrojets. Specifically, using detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet from Brazil (Guara Campaign) and in the auroral elecrojet from Sweden (ERRRIS Campaign), we present comparative observations and general conclusions regarding the observed physical properties of Farley-Buneman two-stream waves and large scale, gradient drift waves. The two stream observations reveal coherent-like waves propagating near the E x B direction but at reduced speeds (nearer to the presumed acoustic velocity) with wavelengths ~5-10m in both the equatorial and auroral electrojet, as measured using the spaced-receiver technique. The auroral elecrojet data generally shows extensions to shorter wavelengths, in concert with the fact that these waves are driven harder. With respect to gradient-drift driven waves, observations of this instability are much more pronounced in the equatorial electrojet, given the more favorable geometry for growth provided by the vertical gradient and horizontal magnetic field lines. We present new analysis of Guara rocket observations of electric field and plasma density data that reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (~10–15 mV/m) in the zonal direction, considerable structure (~5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves.



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Neutral winds in the mid-latitude E-region as deduced from coherent backscatter radar plasma irregularity observations

G.C. Hussey1, C. Meek1, C. Haldoupis2, A. Bourdillon3, and J. Delloue4

1: University of Saskatchewan, Saskatoon, Saskatchewan, Canada ([email protected]) 2: University of Crete, Heraklion, Crete, Greece 3: Universite de Rennes, Rennes, France 4: ALPENS, Paris, France

In the mid-latitude E-region there is evidence suggesting that neutral winds play a significant role in driving the local plasma instabilities and electrodynamics inside sporadic-E layers. The Valensole radar was a mid-latitude northward viewing high frequency (HF) coherent backscatter radar, which could be configured to observe quasi-periodic (QP) echoes in the mid-latitude E-region. It was located in the south of France and had a large azimuthal scanning capability of 82° (24° E to 58° W with 2° angular resolution). Neutral wind motions have been inferred from the striations produced by QP echoes observed with the HF radar when they are displayed in either a range-time-intensity (RTI) or azimuth-time-intensity (ATI) format. These former techniques were only confined to one dimension of motion. The application of the more advanced imaging Doppler interferometer (IDI) technique to the data now supplies two dimensional wind vectors. The results indicate dominant westward neutral wind motions during local pre-midnight and strongly dominant eastward neutral wind motions in the post-midnight hours. This paper presents neutral wind vectors deduced from E-region QP echoes observed with the Valensole HF radar. The results are also compared with other instruments and neutral wind models.

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Evidence of neutral wind drivers for quasi-periodic echo structures in sporadic E layers based on observations from St. Croix and Puerto Rico

M. F. Larsen1, D. L. Hysell2, S. M. Smith3, J. Friedman4, Q. H. Zhou5, and R. L. Bishop6

1: Clemson University, Clemson, South Carolina, USA ([email protected]) 2: Cornell University, Ithaca, New York, USA 3: Boston University, Boston, Massachusetts, USA 4: The Arecibo Observatory, Arecibo, Puerto Rico, USA 5: Miami University, Oxford, Ohio, USA 6: The Aerospace Corporation, Los Angeles, California, USA

During June and July 2002, a 30-MHz imaging coherent scatter radar was installed and operated on the island of St. Croix to view the E-region ionosphere above Arecibo, Puerto Rico. During the observing period, ten events with discernible quasi-periodic echo structure were observed with the coherent scatter radar. In six events simultaneous measurements were made with the Arecibo 430-MHz incoherent scatter radar. The imaging coherent scatter radar allowed us to locate and track the echo structures within the volume illuminated by the transmitter, which shows structures that are generally aligned along wave fronts. A slight preference for wave-front motion toward the southwest is evident throughout the period, but the propagation directions and speeds vary greatly. The incoherent scatter radar measurements show a close correspondence between the occurrence of the coherent echoes and the location of the enhanced electron density structures. In particular, the coherent echoes occur when the electron density layers show uplifts. Simultaneous 557.7-nm optical imager observations on one of the nights shows structure in the



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neutral emissions that corresponds directly to the structure observed with the coherent scatter radar. The propagation of the structures is also consistent. In addition, lidar observations from Arecibo show evidence of neutral uplifts that correspond to the uplifts seen in the plasma density structure. The observations therefore suggest that the neutral motions are the drivers for the instabilities that lead to the quasi-periodic echo structure. The observations will be summarized and the possible relation of the observed structure to gravity waves and neutral shear instabilities will be discussed.

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Low altitude Quasi-Periodic (LQP) echoes studied using long term Gadanki radar observations

N. Venkateswara Rao1, A. K. Patra1, and S. V. B. Rao2

1: National Atmospheric Research Laboratory, Gadanki, India ([email protected]) 2: Department of Physics, S. V. University, Tirupati, India

The quasi-periodic echoes in the lower E-region (well below 100 km), known as LQP echoes, are relatively new observations in the radar investigation of the E region structures and dynamics. They are short periodic (well below Brunt Vaisla period of ~5 minutes) echoing structures, which occur both during daytime and nighttime. The most intriguing aspect is their occurrence in the collision dominated lower E region, where the electron number density is much low as compared to the height of common occurrence of Es. Thus, their occurrence raised important question regarding their generation mechanism.

Although these echoes have been observed at both middle and low latitudes and investigated to address the possible generation mechanism, the investigations made so far are based on limited observations. Investigations have been mostly episodic in nature and the picture that prevails in anyone’s mind is that the occurrence of these echoes is rare. Considering that the occurrence rate could tell how frequently the required conditions can be meet in the ionosphere for their generation, we made an intense effort to address this issue. Accordingly, we carried out extensive experiments on 75 days and 88 nights between June 2004 and March 2007 covering all seasons. This dataset not only allows us to study their occurrence rate, it also allows revealing the type of variability these echoes have in terms of height, time and season.

The Gadanki observations reveal two important statistical results: (1) the occurrence rate of these echoes are 61 % during daytime and 68 % during nighttime and (2) their occurrence shows a strong seasonal variability - maximum in summer (daytime: 58 %, nighttime: 57 %), followed by September equinox (daytime: 32 %, nighttime: 48 %), March equinox (daytime: 26 %, nighttime: 36 %), and minimum in winter (daytime: 25 %, nighttime: 26 %). These suggest that the free energy source providing condition for the growth of these structures are commonly met over Gadanki, which should be considered in any mechanism explaining these structures. Other important aspects, which deserve attention, are: (1) they are often associated with descending echoing region reminiscent of tidal ion layer and (2) wide spectra associated with these echoes with spectral energy extending on a few occasions to ±150 m s-1: The first one indicates the likelihood low-density ion layers at these altitudes playing important role. The descent rates then should relate to the tidal winds playing role forming them, a topic by itself to be investigated for such a low latitude in terms of their formation. Wide spectra clearly indicate the role of electrostatic turbulence in these echoing structures since no neutral turbulence processes is capable of accounting for such a wide spectra. The fact that the required background conditions are met quite frequently and spectral data show wide spectra, a process involving neutral and electro-dynamics is essential. While the seed plasma structures may be considered as due to neutral dynamical effect, the final



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manifestation in terms of small scale irregularities responsible for radar echoes appear to be through a complex neutral-electrodynamical coupling. The Gadanki radar observations of LQP echoes and related detailed analysis will be presented and discussed.

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Differences in the nature of E-region irregularities at the magnetic equator and at 6°N of magnetic equator

S.P. Gupta

Physical Research Laboratory,Ahmedabad 380 009, India ([email protected])

In India we have conducted rocket experiments from Thumba (8.5°N, 77°E, Mag. Lat. =o) and from off equator station SHAR (14°N, 80°E, Mag. lat. 6°N). Rocket flights were conducted nearly simultaneously from both the locations. Similarly V.H.F. radar studies were carried out from equator (Thumba) and off the equator Gadanki (100 km west of SHAR). V.H.F. radar studies at Gandanki and at equator were carried out nearly simultaneously by Krishnamurthy et al (1998), J. Geophy. Res. Vol. 103, p.20761. These studies have been carried out for the last three decades. A good amount of data sets are available covering different seasons and several solar cycle periods. Even though the V.H.F. radar at Gadanki has been in operation for only last fifteen years. Important results which have emerged from these studies are summarised below.

1. Over magnetic equator the irregularities are produced by two stream instability (1-15 m) as well as by gradient drift instability (3-300m) while over off equatorial region only gradient drift instability mechanism is operational.

2. The irregularities have been observed in scale size down to one meter over magnetic equator. However, over off equatorial region, the irregulatiries are observed only upto 3 meter scale size.

3. The layers with km scale sizes have been observed during day time over off equatorial region while such layers were not seen at equator. The observation supports the wind shear mechanism.

4. During day time on several occasions, the irregularities were seen over magnetic equator between 90km-110 km while at off equatorial region such irregularities were not seen in same altitude in a particular time interval. However, the electron density gradients were directed upward at both the locations during this time interval. These observations reveal that the localised effects are dominant in the electric field generation over off the equatorial region on certain occasions.

These aspects will be discussed in this presentation. ________________________________

On possible mechanisms of altitude-extended field-aligned irregularities (FAI), associated with quasi-periodic (QP) radar echoes

S. Shalimov1,2 and T. Ogawa3

1: Institute of Physics of the Earth, Moscow, Russia ([email protected]) 2: Space Research Institute, Moscow, Russia 3: Solar-Terrestrial Environment Laboratory, Nagoya University, Japan

Small-scale field-aligned plasma irregularities (FAI) in the mid-latitude E region associated with quasi-periodic (QP) echoes have been intensively studied since Yamamoto et al. [1991] originally reported the first QP echoes with the MU radar. QP echoes tend to occur in the post-sunset period during the



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summertime as well-defined striations in range-time intensity (RTI) plots. The striations were elongated between 100 km and sometimes up to 130 km apparent altitude [Yamamoto et al., 1994; Ogawa et al., 1995; Saito et al., 2006].

The QP echoes and corresponding irregularities are closely related to rather dense sporadic E (Es) layers [Hussey et al., 1998; Ogawa et al., 2002] and localized plasma density gradients within Es layers [Ogawa et al., 2002]. Also recent observations are consistent with those results in that the echoes appear to originate within the altitude range of enhanced electron densities associated with the sporadic E layer [Larsen et al., 2007].

In recent experimental studies [Larsen et al., 2007] a close correspondence between the intensive neutral motion (upward and downward) and echo structures has been found. This close relationship between the two types of structures indicates that the suspected plasma instabilities responsible for the QP echo production are still ultimately driven by neutral dynamics. We propose a new mechanism of generation of the altitude-extended field-aligned irregularities (FAI), associated with quasi-periodic (QP) radar echoes. FAI can be excited when neutral disturbance caused by an acoustic wave interacts with weakly ionized sporadic E layer plasma and produces small-scale localized density gradients inside the layer. These gradients then generate small-scale field-aligned currents strong enough to be responsible for the excitation of current-driven plasma instability and corresponding FAI.

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Formation and behaviour of sporadic E layers under the influence of vortical-type perturbation excited in the horizontal shear flow

L. N. Lomidze and G. G. Didebulidze

Georgian National Astrophysical Observatory, Ilia Chavchavadze State University, Tbilisi, Georgia ([email protected])

The formation of the mid-latitude sporadic E layers by an atmospheric vortical-type perturbation excited in the horizontal shear flow (horizontal wind with a horizontal linear shear) is investigated. A three-dimensional atmospheric vortical-type perturbation (atmospheric shear wave) can provide a vertical shear of the horizontal wind and cause the convergence of heavy metallic ions into thin and dense layers. The suggested mechanism enables us to explain the short-period oscillations in the Es layers which are characteristic for atmospheric gravity waves in the lower thermosphere. Depending on the shear wave vertical wavelength and the direction of the background horizontal wind, shear wave can also produce the multi-layer structure of the sporadic E. The formation of Es layer by an atmospheric vortical-type perturbation and its temporal development with short-period oscillations is numerically simulated.

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Sporadic E layer climatology derived from CHAMP, GRACE and COSMIC radio occultations – initial results from GFZ Potsdam

C. Arras1, J. Wickert1, C. Jacobi2, S. Heise1 , G. Beyerle1, T. Schmidt1, M. Rothacher1

1: GeoForschungsZentrum Potsdam, Germany ([email protected]) 2: University of Leipzig, Faculty of Physic and Geosciences, Germany



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Sporadic E-layers are patchy thin areas of enhanced electron density in the lower ionospheric E-region which appear mainly during daytime on the summer hemisphere. The knowledge of global sporadic E characteristics is of great interest to radio communications and navigations.

In the last decades sporadic E-layers have been observed by ground based ionosonde and incoherent scatter radar measurements. Starting with the GPS/MET experiment space based sporadic E observations using GPS radio occultation (RO) measurements became more and more important, because they allow global monitoring with high vertical resolution.

Sporadic E-layers cause strong fluctuations of the GPS RO signal amplitudes in signal-to-noise ratio (SNR), which are used to identify the layers. The 50 Hz occultation data is usually starts at about 130 km above the earth’s surface; therefore the altitude interval of sporadic E occurrence (80-120km) is covered.

The German geoscience satellite CHAMP was launched in 2001 and provides a unique long-term data set for sporadic E investigations, which covers already seven years with about 200 globally distributed measurements per day. Data from the six-satellite constellation FORMOSAT-3/COSMIC and the U.S.-German GRACE-A satellite increased the number of daily RO measurements to about 2500 since 2006.

We present initial results of the derivation of sporadic E information from the multi-satellite GPS RO data set. The analysis technique is introduced, which is based on the evaluation of the SNR fluctuations of the occultation signals. We also introduce first climatologies of sporadic E occurrence, derived from the long-term CHAMP data set. We demonstrate the significantly increased potential of the GPS RO data for sporadic E investigations by using the multi-satellite data set from CHAMP, GRACE and COSMIC, which allows for global investigations with significantly increased resolution in time and space.

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E-region ionospheric drift measurements during sporadic E-layer occurrence using Digisonde DPS-4

D. Kouba1,2, P. Šauli1, J. Boška1, and O. Santolík1,2

1: Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic ([email protected]) 2: of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic

Our contribution is focused on the ionospheric plasma motion at the height range 90-150 km (corresponding to the E-region ionosphere). Study involves observations from midlatitude ionospheric station Pruhonice (50N, 14.6E) using DPS4 equipment during period of low solar activity (2006-2007).

Raw data are manually checked and controlled using skymap points selection method. During summer periods of 2006 and 2007 we performed special campaigns of 'Es drift' measurement. Together with standard E measurement (2-2.6 MHz) we recorded plasma motion each 15 minutes also on higher sounding-frequency window (3.2 - 4.7 MHz).

Our results show different behaviour of plasma motion in the 'E' and 'Es' layers. This fact confirms drift velocity height dependence in interval 90 - 150 km and calls for careful interpretation of the E-drift during presence of Es layer.

Our preliminary results show E-region statistical drift behaviour for both, E and Es cases. We independently analyse vertical and horizontal velocity components and using histograms we also found prevailing directions of plasma motion corresponding to specified ranges of velocities.



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Seasonal variations of low-latitude sporadic-E and field aligned irregularities and their relation to sporadic meteor flux

D.V.Phanikumar1, A.K.Patra1, K. Kishorekumar2, and G.Yellaiah3

1: National Atmospheric Research Laboratory, Gadanki, India ([email protected]) 2: Space Physics Laboratory, Trivandrum, India 3: Department of Astronomy, Osmania University, Hyderabad, India.

The formation of sporadic-E layers (Es), through ‘windshear’ theory is now accepted as the mechanism responsible for the formation. In this theory vertical shears in the horizontal wind can drive the long-lived metal ions in the ionosphere to move vertically and converge into dense plasma layers. The meteor trails in the E-region have known to provide the extra ionization in forming the metallic layers. The non-shower meteors penetrating in these altitudes provide a long term effect on the metallic ion layer formations. Although this is known since four decades, the formation of sporadic-E layers has remained a mystery about the close relationship with the annual variation of sporadic-E layer strength and that of meteoric deposition rates. Although the earth receives annually more of non-shower meteors than the shower meteors it is expected that these shower meteors are capable of supplying necessary electron density gradients and electric fields thus provide necessary electron density gradients. These electric fields can play a vital role in modifying electric fields associated to the large scale plasma waves. It is to be mentioned that the additional ionization due to meteor trail can affect instantaneously the Field Aligned Irregularities (FAIs) characteristics of the large scale gradient waves thus directly influencing their strength. The relationship between sporadic-E and FAIs is known to be well correlated at mid-latitudes. However, at low-latitudes the relationship between Es and FAIs is not known yet. The occurrence and strength of sporadic E layers and E-region FAIs whether it depends directly on the metal ion content, which apparently is determined primarily by the meteoric deposition is not known exactly as there is no observational eveidence to the present date. In this context, an experiment is conducted by using Indian MST Radar of E-region FAIs and ionosonde operated from a nearby location SHAR for sporadic-E observations and seasonal variation of sporadic meteors from a nearby location, Trivandrum to understand the inter-relationship between meteor, Es and FAIs.

Recent studies at mid-latitude showed that seasonal variations of sporadic meteors are well correlated with seasonal variation of sporadic-E layers and meteor trails across or along the geomagnetic field at mid-latitudes have been simulated to explain the generation of FAIs. Observations show that seasonal variations of daily count of sporadic meteors show summer maximum and a secondary peak in winter and minimum in equninoxes. In this paper, seasonal variation of sporadic-E and E-region FAIs and their relation to the seasonal dependance of sporadic meteors are presnted and discussed in the light of present understanding.

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Sporadic-E observations at Jicamarca?!

Akshay Malhotra1, John D. Mathews1, and Julio Urbina1

1: The Pennsylvania State University, University Park, PA, USA ([email protected])

Considerable progress has been made in the study of mid-latitude Sporadic-E, which is well documented, but comparatively lesser progress has been made in the study of equatorial Sporadic-E. Indeed, it is unclear if Sporadic-E has been observed at all near the geomagnetic equator using any technique other



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than the ionosonde. In particular, there have been no reports of Sporadic-E observed using the Jicamarca Radio Observatory (JRO) 50 MHz radar. The overwhelming—in SNR terms—presence of the nearly ubiquitous Equatorial ElectroJet (EEJ) is the likely reason Sporadic-E has not been reported at JRO as well as at other similar radars near the geomagnetic equator. We present here what we believe to be the first Sporadic-E (defined here as altitude-narrow E-region layers that last 10’s of minutes) observations from JRO based on radar campaigns carried out in June 2006 and 2007: The structure and characteristics of these equatorial Sporadic-E layers is compared with the mid-latitude counterpart and found to be similar at least in that a “convergence zone” is identifiable. We also demonstrate what we suggest is the immediate effect of meteor-produced ionization on the formation and evolution of the magnetic-equatorial Sporadic-E layers.

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Meteor plasma trails in E region: diffusion, electric fields, and ionospheric disturbances

Y. S. Dimant and M. M. Oppenheim

Center for Space Physics, Boston University, Boston, USA ([email protected])

Meteoroids penetrating the Earth's atmosphere frequently leave behind dense plasma trails between 75 km and 130 km altitudes. These trails are responsible for a significant part of the radar scattering from the E-region ionosphere. Low-power, small-aperture radars detect specular echoes which occur only when the trail lies perpendicular to the radar line-of-sight. High-power, large-aperture VHF and UHF radars observe head echoes, short duration signals traveling with the ablating meteoroids, and non-specular echoes, long duration signals spanning a broad altitude range resulting from scatter from turbulent electron density irregularities generated by plasma instabilities. Modeling both specular and non-specular radar echoes requires knowledge of the distribution of trail plasma which depends on the electric fields generated by the trail. This paper presents the first quantitative model of the fields and density evolution which accounts for both the geomagnetic field and the background E-region plasma.

Using both simulations and 2D analytical theory, we model trail evolution for a broad range of conditions. Under all conditions, our model shows that ambipolar diffusion of trails gives rise to polarization electric fields which are sharply anisotropic because of currents propagating large distances along the geomagnetic field, B. These fields generate electron density disturbances and drive plasma instabilities, both in the trail and in the background ionosphere. Our new model estimates the spatial distribution of a trail’s ambipolar electric field and the non-turbulent diffusion rates, both parallel and perpendicular to the geomagnetic field. It predicts that dense trails evolve from slow anisotropic to more rapid isotropic diffusion. Also, this transformation occurs much sooner during the day than during night because of higher daytime E-region plasma densities. Recent radar observations near magnetic equator (Jicamarca, Peru) have confirmed these predictions.

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Meteor trails in the ionosphere: day/night and altitude differences

G. Sugar1, M.Oppenheim1, E. Bass1, Y. Dimant1, and J. Chau2

1: Boston University, Massachusetts, USA ([email protected]) 2: Jicamarca Radio Observatory, Lima, Peru



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Using the high-power, large-aperture radar at the Jicamarca Radio Observatory (JRO) in Peru, we found evidence for a dramatic difference between meteor trails during the day than the night. In a 20 minute interval of nighttime on July 12, 2005, we found 1288 head echoes and 341 trails, while during a 20 minute interval during daytime on the same day we found 1240 head echoes and only 50 trails. A second experiment conducted on July 17, 2007 produced similar results: 1057 heads and 87 trails during a 30 minute interval in the day, and 401 heads and 185 trails during 30 minutes of night. There was significant electrojet interference during the nighttime sample which caused both the head total and the trail total to decrease. This difference between day and night trails almost certainly results from the increased daytime plasma density. Oppenheim and Dimant [JGR, 2007] argued that higher background plasma densities will enable background currents to more rapidly move to cancel the trail's ambipolar electric field and this eliminates the instability driver. This poster will discuss these results and how trails vary as a function of altitude and duration.


Poster P2: Posters for Session S6 (F-region plasma irregularities: causes and effects)

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The simultaneous rocket observation of electron density and temperature inside the equatorial spread-F bubble and their numerical simulation

F. C. de Meneses, P. Muralikrishna, and E. Alam Kherani

Instituto Nacional de Pesquisas Espaciais (INPE), Brazil ([email protected])

The ionospheric irregularities associated with spread F were first observed from the rocket flights 40 years ago. Such in-situ measurements provides useful information regarding the development of plasma depletions or bubbles and subsequent generation of small scale irregularities. These measurements have been used to obtain the power spectrum of fluctuations associated with the equatorial spread F. An equatorial station Alcantara (2.31oS, 44.4oW) in Brazil has a rocket launching facility. From this station, rocket carrying Langmuir probe was launched on 18th December 1995 at 21:17 LT. The electron density and temperature were measured from the Langmuir probe. This in-situ measurement identify the depletions along the trajectory of the rocket. Together with the density fluctuations, the temperature fluctuations are also noticed. The simultaneous measurements of density and temperature provides insight into the energetics of the spread F phenomena. The two dimensional numerical model is developed to simulate these fluctuations. The model solves the hydromagnetic equations (continuity, momentum, energy and Poisson equations) in a plane perpendicular to the terrestrial magnetic field. The measurements and numerical results are further discussed to understand the energetics of the bubble.

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The solar wind and geomagnetic storm effects on generation of the equatorial scintillation

L. Biktash

Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Acad. Sciences (IZMIRAN), Troitsk, Moscow region, Russia ([email protected])

The solar wind and geomagnetic storms cause a wide spectrum of irregularities and processes which are generated from the polar ionosphere to the equatorial ionosphere. However, the space weather effects the on the equatorial ionospheric phenomena are not studied completely and the physical nature of many penetration mechanisms from the Polar Regions to the equatorial ionosphere has not been completely understood. The classical picture of the ionospheric storm is confirmed by many observations. Nevertheless, the ionospheric storm event remains the most complex one in the upper atmosphere. The solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere - ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the Polar Regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this



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difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that the factor, which presents during magnetic storms to fully inhibit scintillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind. Taking into account the time delay between the solar wind and the ionosphere phenomena, the relationship between the solar wind and the ionosphere parameters can be used for predicting of scintillations.

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Observation of MSTIDs in the Brazilian sector possibly associated with tropospheric disturbances at mid-latitudes

C.M.N. Candido1, A.A. Pimenta1, C. M. Wrasse2, Y. Sahai2, and F. Becker-Guedes2

1: Instituto Nacional de Pesquisas Espaciais – INPE ([email protected]) 2: Universidade do Vale do Paraíba – UNIVAP

The OI 630 nm emission all-sky imaging observations have been carried out at Cachoeira Paulista (22.3º S, 45.0º W), Brazil, over several years. Recent analysis of some observations obtained earlier during several nights have indicated the presence of dark bands structures entering in the field of view of the imaging system coming from southeast direction and propagating to northwest. These observations possibly indicate the propagation of medium scale traveling ionospheric disturbances (MSTIDs) to low latitudes but generated at mid-latitudes. In this communication, we present the OI 630 nm all-sky observations obtained on the nights of 31 May - 01 June 1997, 18 - 19 July 1998, 28 - 29 July 1998 (all geomagnetically quiet nights) with ionospheric sounding observations carried out C. Paulista. Meteorological satellite (METEOSAT) observations on these nights and the winds and omega (Pa/s) taken from NCEP showed intense tropospheric disturbances in the mid-latitudes. This possibly indicates that the source for the MSTIDs observed at C. Paulista may be tropospheric disturbances located in the mid-latitude region. It should be mentioned that the ionospheric data obtained at C. Paulista indicates that the dark bands structures propagating to northwest direction are also associated with the F-region uplifting indicated by the minimum virtual height (h′F), F-region peak density(foF2) depletions, and spread-F occurrence.

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A study of the mean properties of equatorial ionospheric plasma depletion drift velocities determined from far-ultraviolet spacecraft observations

S.L. England1, T.J. Immel1, S.H. Park2, H.U. Frey1, and S.B. Mende1

1: Space Sciences Laboratory, University of California Berkeley, California, USA ([email protected]) 2: Department of Mechanical Engineering, California State University, Sacramento, California, USA

The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity



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of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. The automation of this process has also allowed for the routine tracking of a large number of depletions and the determination of their velocities as a function of magnetic latitude as well as local time. Here we study the average properties of this motion during early 2002: This globally-averaged perspective show remarkable agreement with the local time and latitudinal dependence of the zonal drift velocity observed by ground-based instruments that have provided detailed information in a few locations around the planet. We introduce a simple empirical model of our observations that reproduces both the local time and latitudinal variations. A comparison of both our observed and modeled zonal drift velocities with winds from the Horizontal Wind Model (HWM-93) reveals good agreement, providing evidence of the strong coupling between F-region nighttime winds and the plasma depletion drift velocities.

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Three-dimensional equatorial Spread F modeling

J.D. Huba1 and G. Joyce2

1: Plasma Physics Division, Naval Research Laboratory, Washington, DC ([email protected]) 2: Icarus Research, Inc., Bethesda, MD

The Naval Research Laboratory (NRL) has recently developed a new three-dimensional code to study equatorial spread F (ESF). The code is based on the comprehensive NRL 3D ionosphere model SAMI3 and includes a potential equation to self-consistently solve for the electric field. The model assumes equipotential field lines so a 2D electrodynamic problem is considered. In this study a narrow wedge of the post-sunset ionosphere is simulated. It is found that (1) bubbles can rise to 1600 km, (2) extremely steep ion density gradients can develop in both longitude and latitude, (3) upward plasma velocities approach 1 km/s, and (4) the growth time of the instability is 15 min. These results are shown to be consistent with radar and satellite observations.

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Characteristics of anomaly of HF radio wave arrival direction observed near the evening terminator

M. Ishii1, T. Maruyama1, and I. Kimura2

1: National Institute of Information and Communications Technology, Tokyo, Japan ([email protected]) 2: Kyoto University, Kyoto, Japan

The evening enhancement or prereversal enhancement (PRE) is a phenomenon in which the upward ExB drift velocity increases for one to two hours just before the reversal of drift direction from up to down around dusk terminator. This phenomenon is known to have a large day-to-day variability and a tight connection with plasma bubble onsets. NICT has a project to detect ionospheric irregularities for early warning against the advanced utilities of satellite positioning system since 2002: In this study, we use these data for deducing the character of PRE. We deployed an HF radio wave direction finding system at Oarai, Ibaraki and received broadcasting radio wave from Australia across the equator region. The results show that the variation of HF arrival angle has clear seasonal dependence; namely, it becomes large in spring and fall, which are active seasons of PRE. In addition, we use theoretical model of HF ray tracing for deducing the relation between HF arrival angle and pre-reversal enhancement. We deduce the



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influence of arrival angle with some simple anomaly of electron density in the model. We discuss the relation between radio wave arrival direction and PRE in the clear events.

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Peculiar properties of the topside ionograms at the equatorial latitudes

A. T. Karpachev

IZMIRAN, Troitsk, Moscow region, Russia ([email protected])

The features of the topside ionograms at the equatorial anomaly, EA, latitudes obtained on board the Intercosmos-19 satellite during high solar activity are considered. On passing the EA latitudes the diffuse reflections first appear just over the F2 layer maximum and then occupy the higher altitudes. In a presence of the strong density gradient on the outside slope of the EA crest the aspect scattering on the small-scale irregularities under the action of the gradient-drift instability is observed at the topside ionograms. The “double ionograms” are observed in the low latitude “hole” (decrease) in hmF2 at the southern winter EA crest latitudes. The ionograms with typical equatorial F-spread are shown which is connected with both signs irregularities (+ΔNe and -ΔNe) located both over and under the F2 layer maximum. The waveguide propagation in the ducts with the reduced electron density and with strong reduced density (bubbles) is considered. The scheme of the equatorial F3-layer formation is presented. The distributions of the F-spread probability in the EA region for the various geophysical conditions are built. The reasons of the observed features are discussed.

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An analysis of the lower topside ionospheric scale heights based on the electron density profile retrieved from FORMOSAT/COSMIC radio occultation

measurements

Libo Liu, Maosheng He, Weixing Wan, and Man-Lian Zhang

1: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China ([email protected])

Knowledge of the spatial distribution of electron number densities in the ionosphere, especially the height profile Ne(h), is essential for ionospheric studies as well as related practical applications. It is well known that the scale height is one of the important ionospheric characteristics, due to both a measure of the shape of the electron density profile and its intrinsic connection to the ionospheric dynamics, plasma thermal structure and compositions. However, the knowledge of the behavior of ionospheric scale heights remains insufficient, especially in the topside ionosphere.

In this report, we analyze the ionospheric scale heights in the lower topside ionosphere which are derived from the electron density profiles retrieved from the FORMOSAT/COSMIC radio occultation observations. A database contains about 2000-3000 profiles each day over altitudes from 160-600 km during years 2006 and 2007: The vertical scale height (VSH) is deduced from the electron concentration profiles defined as the value of -dh/d(ln(Ne)), and the effective scale height (Hm) is defined as the scale height in the Chapman-α function to approximate the Ne profiles. The VSH and Hm are derived in order to investigate their diurnal and seasonal variations and latitudinal and longitudinal dependences. We will report that the derived VSH and Hm show marked diurnal and seasonal variations. The features of the global behavior of scale heights will also be presented in this report.



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ACKNOWLEDGMENTS The Radio occultation data are provided by the UCAR database web. This research was supported by National Natural Science Foundation of China (40725014), and National Important Basic Research Project (2006CB806306).

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The Simultaneous occurrence of airglow structures associated with ESF and MSTIDs in the southern hemisphere

C. Martinis, J. Baumgardner, and M. Mendillo

1: Boston University, Boston, MA 02215, USA ([email protected])

Boston University operates an all-sky imager (ASI) located at El Leoncito, Argentina (31.8o S, 69.3o W, 18o S mag lat). A typical equatorial/low latitude phenomenon observed is related to airglow depletions associated with the Rayleigh-Taylor instability (RTI). Another kind of process has been found to occur, but much less frequently. Observations show dark/bright bands tilted with respect to the geomagnetic meridian moving north-westward. These are typical characteristics of mid-latitude features associated with the Perkins or coupled Es-F region instabilities, commonly known as medium scale traveling ionospheric disturbances (MSTIDs). We present here a few cases in which both features, airglow depletions associated with RTI and airglow bands associated with mid-latitude instabilities, are seen simultaneously in the northern and southern parts of the ASI's field of view. This is a unique situation in which two different electrodynamical phenomena have been detected simultaneously, indicating the presence of a transition region.

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Onsets of equatorial plasma bubble and ionosphere-thermosphere system

T. Maruyama, S. Saito, M. Kawamura, and K. Nozaki

1: National Institute of Information and Communications Technology, Tokyo, Japan ([email protected])

To examine ionosphere-thermosphere conditions that lead to onsets of equatorial plasma bubbles, nocturnal ionospheric height variations were analyzed using ionosonde data obtained along the magnetic meridian of 100deg.E; two ionosondes were installed near the magnetic conjugate points, Chiang Mai, Thailand (18.8deg.N, 98.9deg.E; 13.0deg. Magnetic latitude) and Kototabang, Indonesia (0.2deg.S, 100.3deg.E; -10.0deg. Magnetic latitude), and the third ionosonde was installed near the magnetic equator, Chumphon, Thailand (10.7deg.N, 99.4deg.E; 3.3deg. Magnetic latitude). Ionospheric virtual heights were scaled every 15 minutes and vertical EXB drift velocities were inferred from the equatorial data. Incorporating the inferred vertical drift velocity, assuming equipotentials of the magnetic field lines, no-wind ionospheric bottom heights were modeled over the two low-latitude conjugate stations. The deviation of the heights from the model outputs was used to infer the transequatorial thermospheric wind. The results were compared for the September and March equinoctial periods, in which plasma bubbles occur frequently at these longitudes.

A higher order oscillation, with a period of about 7 hours, of the transequatorial meridional wind was observed in both the periods, and its amplitude was significantly larger in September than March. Also the maximum ionospheric height over the magnetic equator during evening hours was higher in March than September. These equinoctial asymmetries of the ionosphere-thermosphere system were tightly connected with the previously-reported equinoctial asymmetry of the occurrence probability of equatorial ionospheric irregularities. In other words, a higher order oscillation of the meridional wind



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might be involved with onsets of plasma bubbles. Although the observed equinoctial asymmetry of the bubble occurrence is not very prominent compared with other morphological features, it would be a key to testing possible connections between the plasma bubble and the lower atmosphere, because direct solar influence to the ionosphere-thermosphere system is expected to be identical in both the equinoxes.

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Dynamical simulation of electromagnetic Spread F

M. Mascarenhas, E. Alam Kherani, J. H. A. Sobral, and E. R. de Paula

1: National Space Research Institute, São José dos Campos, Brazil ([email protected])

We present a three-dimensional simulation of electromagnetic bubble generation and evolution in the equatorial-low-latitude F region of the ionosphere. The bubble is generated by the Rayleigh-Taylor instability mechanism. The unstable Rayleigh-Taylor plasma modes are believed to be electrostatic modes due to the large conductivity parallel to the magnetic field. However, the recent CHAMP observations indicate the presence of magnetic field fluctuations associated with bubble currents. These fluctuations are caused by the currents inside and around the bubble. In order to understand the current system associated with the bubble in the equatorial-low-latitude ionosphere, we carry out the simulation in the framework of hydromagnetic theory. In this framework, the plasma fluid equations along with the complete Maxwell equations are solved. We have found that the electric field parallel to the terrestrial magnetic field diffuses away rapidly and so it does also the toroidal component of magnetic field fluctuation also. The large Pederson current inside the bubble, however, drives the large poloidal magnetic field fluctuation in and around the equator.

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Can equatorial spread-F (ESF) occur on other planets?

Michael Mendillo1, Jon Niehof1, Katherine Garcia1, Christina Prested1, Sarah McGregor1, Nicholeen Viall1, Luke Moore1, Paul Withers1, Carlos Martinis1, and Andrew Stephan2

1: Boston University, Boston, MA 02215, USA ([email protected]) 2: Naval Research Laboratory, Washington, DC, USA

Observations of ionospheres on other planets started in the 1960s. In nearly 50 years of research on the topic, theoretical and modeling studies have concentrated on understanding the vertical structure of planetary electron density profiles, together with their diurnal, seasonal, latitudinal and solar cycle behavior. The data available from Venus and Mars are more abundant than from Jupiter and Saturn, and there are only a few observations from Uranus and Neptune. In the past several years, the more abundant data sets from Mars and Saturn have revealed two interesting trends: (1) at Mars, Ne(h) profiles above the planet’s crustal magnetic fields are far more structured than those above regions that are non-magnetized, and (2) virtually all Ne(h) profiles at low latitudes at Saturn are highly structured. In this paper, we assess the impact that the gravitationally-driven Rayleigh-Taylor plasma instability may have as one possible source of plasma irregularities found above nearly-horizontal magnetic fields on Mars and Saturn.



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Reception of TV broadcast radio waves associated with equatorial plasma bubbles

H. Nakata1, Y. Kinoshita1, Y. Otsuka2, T. Takano1, S. Shimakura1, K. Shiokawa2, and T. Ogawa2

1: Chiba University, Chiba, Japan ([email protected]) 2: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan

The continuous observation of VHF radio waves at Tateyama, Japan (34.9N, 139.8E), since 2001 shows that broadcast radio waves transmitted from Southeast Asia (e.g. the Philippines, Thailand) are frequently received after sunset in equinox seasons during solar maximum. In conjunction with these receptions of the radio waves, equatorial plasma bubbles are observed by all-sky imagers at Sata, Japan (31.0N, 130.7E) and Darwin, Australia (12.4S, 131.0E). Nakata et al. (2005) have shown that radio waves transmitted from the Philippines propagate to Tateyama when an equatorial plasma bubble is located at the west of Japan and develops higher latitude than 27N. This is confirmed by a ray-tracing calculation which includes scattering by field-aligned irregularities. Since radio waves transmitted from Thailand are also received, therefore, the relationship between equatorial plasma bubbles and the reception of the radio waves transmitted from Thailand is examined in this study. From a ray-tracing calculation with electron density distributions determined by IRI, it is shown that the radio waves do not propagate to Japan due to equatorial plasma bubbles. At Okinawa (geographic: 26.7N, 128.2E, geomagnetic latitude: 17.0N), however, the monthly average of the daily maximum of electron density determined by the ionosonde is 1.3-1.5 times as large as determined by IRI in 2001: As for the electron density at Guangzhou (geographic: 23.1N, 113.4E, geomagnetic latitude: 12.9N), on the other hand, daily maximum of NmF2 determined by the ionosonde are comparable to or less than IRI. Since the latitude of Okinawa is higher than Guangzhou, this implies that the equatorial anomaly developed to higher latitude due to the enhanced eastward electric field which is indispensable for generating EPBs. Actually, the radio waves propagate to Tateyama using the modified electron distribution. In addition, radio waves transmitted from the Philippines also propagate to Tateyama at the same time. This is consistent with the observation.

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Occurrence characteristics of plasma bubble studied with global ground-based GPS receiver networks

M. Nishioka1, A. Saito1, and T. Tsugawa2

1: Kyoto University, Kyoto, Japan ([email protected]) 2: National Institude of Information and Communications Technology, Tokyo, Japan

Occurrence characteristics of plasma bubble were studied with ground-based GPS receiver networks. Plasma bubble can be detected with Total Electron Contents derived from dual-frequency GPS receiver data. The occurrence rate of plasma bubble detected by the global GPS networks has higher spatial and temporal resolution than that detected by the other observational techniques because of its wide coverage in time and space. The occurrence characteristics of plasma bubble were studied in detail with this novel data set. Twenty three GPS receivers around the dip equator were used to reveal the occurrence from 2000 to 2007: Monthly and semiannual occurrence rates for eight years were derived in five regions, which were the Asian, African, Atlantic, Eastern Pacific, and Central Pacific regions. Characteristics of the monthly occurrence rates were different among the regions. Although it was found that sunset time lag



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effect plays an important role for the monthly variation, two asymmetries which could not be explained with the sunset time lag scenario were found: (1) asymmetry between two solstices and (2) asymmetry between two equinoxes. (1) was found in the African, Asian, Eastern Pacific, and Atlantic regions. In the African and Asian regions, occurrence rates in the June solstice season were larger than those in December. In the Eastern Pacific and Atlantic regions, occurrence rates in the December solstice season were larger than those in June. Seasonal variation of Pedersen conductivity integrated along the geomagnetic field line in F-region can be attributed to this solstice asymmetry. (2) was found especially in the Central Pacific region. In the Central Pacific region, the occurrence rate in the September equinox was much larger than that in the March equinox. Semiannual occurrence rates from 2000 to 2007 were used to study the year-to-year variation from the high solar activity period to the low solar activity period. The dependency of the occurrence on the solar activity was different among the regions. The strongest dependence was found in the Asian region, where the occurrence rate decreased from 70% in 2002 to 10% in 2006: In the Atlantic region, the occurrence rate was between 20% and 40% and didn’t show linear decrease against the solar activity. Occurrence rates against the latitude/altitude were investigated in the Asian region in 2004: It was found that the occurrence was high and constant for a station whose Height On the Dip Equator (HODE) was less than 700km. They began to decrease when HODE was higher than 700km, and was almost zero where it was higher than 900km.

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Magnetic signatures of plasma blobs as observed by the CHAMP satellite

Jaeheung Park, Claudia Stolle, Herrmann Lühr, and Martin Rother

1: GeoForschungsZentrum, Potsdam ([email protected])

We investigated the magnetic signatures of plasma blobs as observed by the CHAMP satellite. In total, we have identified ~50 blobs with clear density enhancements and magnetic signatures. In each blob the magnetic field strength was depressed, and the components perpendicular to the main field showed fluctuations. The variation in magnetic field strength implies that enhanced plasma pressure is balanced by a magnetic pressure reduction, and the deflection in the perpendicular components indicates the presence of field-aligned currents. Both characteristics are consistent with bubble magnetic signatures [Stolle et al., 2006]. Concurrent observations of CHAMP (at ~350 km altitude) with ROCSAT-1(~600 km), STSAT-1(~680 km), and DMSP F15(~840 km) strongly suggest that the blobs have a field-aligned structure spanning several hundred kilometers. We also investigated the seasonal/longitudinal distribution of the detected blob events. From that a rough coincidence with the bubble occurrence distribution is found although it is biased heavily towards the winter hemisphere. Plasma blob encounters at CHAMP altitude are quite frequent, even after local midnight. We believe that our results corroborate the close relationship between equatorial plasma bubbles and blobs.



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Relevant aspects of thermospheric dark band structures observed by ground-based optical and radio techniques over the Brazilian low-latitude sector

under different solar activity conditions

A.A. Pimenta1, C.M.N. Candido1, D.C.M. Amorim1, Y. Sahai1,2, J.A. Bittencourt1, P.R. Fagundes2, and Gobbi1

1: Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP, Brazil 2: Universidade do Vale do Paraíba (Univap), São Jose dos Campos, SP, Brazil

Using ground-based measurements we investigate the occurrence of dark band structures in the OI 630 nm nightglow emission all-sky images in the Brazilian low latitudes region during the periods from January 1990 to December 1990 and from January 2000 to December 2000 (high solar activity period; average 10.7 cm solar cycle flux 122210180 −−−> HzWmx ), January 1995 to December 1996 (low solar activity period; average 10.7cm solar cycle flux 12221090 −−−< HzWmx ) and from January 1997 to December 1999 (ascending solar activity period; average 10.7 cm solar cycle flux from 122210130 −−− HzWmx to 122210170 −−− HzWmx ). The OI 630 nm images obtained during these periods show thermospheric Dark Band Structures (DBS) in low latitudes region propagating from southeast to northwest. These dark patches moved with average speed of about 80-250 m/s at an altitude of 220-300 km, which is the typical altitude range of the OI 630.0 nm airglow emission. Also, digisonde observations registered abrupt increases in both the F-layer peak height (hmF2) and base height (h’F) when the low intensity band passed over Cachoeira Paulista. During the period studied a strong solar cycle and seasonal variations were noticed in the DBS. Only during low solar activity period (LSA) and ascending solar activity period (ASA) the DBS occurrences were observed in the OI630 nm nightglow emission all-sky images. It should be pointed out that these thermospheric/ionospheric events are not related to geomagnetic disturbed conditions. In this paper we present important features from these set of observations in the nighttime thermosphere/ionosphere under different solar activity conditions. A possible mechanism for generation of these dark band structures is presented.

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Using the JULIA dataset to find evidence of preconditioning of ESF in bottom-type layers

H. Pinedo1, J. L. Chau1, and D. Hysell2

1: Radio Observatorio de Jicamarca, IGP, PERU ([email protected]) 2: Department of Earth and Atmospheric Sciences, Cornell University, USA

Recently Hysell et al. [2005] suggested that the periodic structuring observed in the bottom-type scattering layers might be used to forecast full-blown equatorial spread F (ESF). The seed or precursor waves may be generated by collisional shear instability. Preliminary observations at Jicamarca and ALTAIR have shown that such structures present wavelengths of the order of tens or hundreds of kilometers. At Jicamarca periodic structures have been observed using in-beam radar imaging techniques, however such observations are limited to few days during the last five years. However, the JULIA system at Jicamarca has been doing observations since 1996, using interferometry and dual-beam configurations with very narrow beams. The JULIA dataset is approximately 100 days per year on average. The bottom-type irregularities drift has a relatively constant speed in the westward direction; given that the JULIA beams



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are very narrow (~1o) the corresponding spatial periodicities might be observed as temporal periodicities in typical range-time intensity maps. The zonal drift velocity is obtained from interferometry. In this work we present the statistics of the observed bottom-type periodicities and the occurrence of ESF plumes detected with the JULIA system, the collocated digisonde and/or the scintillation receivers at Ancon (west of Jicamarca). The latter instruments might help us to correlate the bottom-type structures over Jicamarca with the plumes observed tens or hundreds of kilometers East and West of Jicamarca.

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Plasma bubbles in the topside ionosphere: high solar activity period

L. Sidorova

Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation (IZMIRAN), Troitsk, Moscow region, Russia ([email protected])

The present study deals with the He+ density depletions (subtroughs), observed during a high solar activity. There are the indications that plasma bubbles, produced by Rayleigh-Taylor instability at the bottomside of ionosphere, could rise up to the topside ionosphere and plasmasphere. Maryama and Matuura (1984), using ISS-b satellite data (high solar activity period, 1978-79), have seen the plasma bubbles in Ne density over equator at 1100 km altitudes in 46 cases in 1700 passes. That is ~3% only. However, there is distinctly another picture in He+ density depletions (subtroughs) according to ISS-b data for the same period. He+ density subtroughs occur in the topside ionosphere over equatorial and low-latitudinal regions (L~1.3-3) in 11% of the cases (Karpachev, Sidorova, 2002; Sidorova, 2004, 2007). The detailed statistical study of the He+ density subtrough peculiarities was done. The subtrough depth (depletion value) as function of local time (evening–night hours) was compared with the vertical plasma drift velocity variations, obtained for the same periods from AE-E satellite and IS radar (Jicamarca) data. Striking similarity in development dynamics was revealed for the different seasons. It was noted also that the He+ density subtroughs are mostly observed in the evening-night sector (18-05 LT) from October till May. It was like to the peculiarities of the equatorial spread-F (ESF), usually associated with plasma bubble. The monthly mean He+ density subtrough occurrence probability, plotted in local time versus month, was compared with the similar plots for ESF occurrence probability, derived by Abdu and colleagues (2000) from ground-based ionograms obtained over Brazilian regions for the same years. The comparison shows good enough correlation (R=0.67). Moreover, it was revealed that there are many cases of the He+ density subtrough observations on the OGO-4 (1968 - solar maximum, 20th cycle), the OGO-6 (1969 - solar maximum, 20th cycle) and DE-2 (1981 - solar maximum, 21th cycle) data. It was concluded, that the He+ density depletions should be considered as originating from equatorial plasma bubbles phenomena, or as possible fossil bubble signatures. It was also concluded that the He+ density depletions are rather typical phenomena for the topside ionosphere for high solar activity epoch. The possible reasons of the He+ density depletions occurrence as function of solar activity are discussed.

References

Maryama, T. and N. Matuura, Longitudinal Variability of Annual Changes in Activity of Equatorial Spread F and Plasma Bubbles, Journal of Geophysical Research, Vol.89, N A12, P.P. 10,903-10,912, December 1, 1984.

Karpachev, A.T. and L.N. Sidorova, Occurrence probability of the light ion trough and subtrough in Не+ density on season and local time, Adv. Space Res. 29, 999-1008, 2002. Sidorova, L.N., He+ density topside modeling based on ISS-b satellite data, Adv. Space Res., 33, 850-854, 2004.

Sidorova, L.N. Plasma bubble phenomenon in the topside ionosphere , Adv. Space Res., Special issue (COSPAR), doi: 10.1016/j.asr.2007.03.067, 2007.



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Abdu, M.A., J.H.A. Sobral, I.S. Batista, Equatorial spread F statistics in the american longitudes: some problems relevant to ESF description in the IRI scheme, Adv. Space Res., 25, 113-124, 2000.

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Morphological study of equatorial plasma bubbles using GPS L-band scintillations over Indian region

S. Sripathi, S. Bose and A. Bhattacharyya


In this paper, we present the results of a morphological study of amplitude scintillations on L1 frequency (1.575 GHz) over the Indian region during the years 2004-2005 in the declining phase of solar cycle 23 obtained under the GAGAN (GPS And Geo-Aided Navigation) project for (a) quiet and (b) magnetically disturbed conditions. The GAGAN project has 18 ground GPS receiver stations all over India operating on a continuous basis. Using this data, occurrence of amplitude scintillations on the GPS L1 (1.575 GHz) signal recorded at several stations has been investigated using the strength of L-band scintillations as measured by the S4 index, which is the standard deviation of normalized intensity fluctuations. The latitudinal and temporal variation in the occurrence suggests that scintillations occur predominantly over equatorial ionization anomaly (EIA) region and during 20-21 LT. Further, the observations suggests that while L-band scintillations are found to be more dominant for both the equinox periods as compared to the solstice months as expected, they also reveal that there is an asymmetry in the occurrence of scintillations for the two equinox periods. We find that occurrence of L band scintillations is greater for the vernal equinox ( February, March, April) than for the autumnal equinox (August, September, October). Further, the occurrence of scintillations is found to extend to higher latitudes in the vernal equinox than for the autumn equinox. The observations also indicate that occurrence of L-band scintillations is greater for 2004 than for 2005 with average annual mean sunspot number varying from 40.4 in 2004 to 29.8 in 2005. The new observation is that occurrence of L-band scintillations extends to hours beyond 23:00 IST only for a narrow band of 60-80 days in the March equinox. In order to understand this aspect, we have used TIMED GUVI retrieved Peak electron density over Indian region during the same period. The peak electron density is compared with the scintillation occurrence characteristics. The comparison suggests that peak electron density during March equinox is dominant over that during Vernal equinox suggesting the role of background electron density in the occurrence of L-band scintillations. Apart from this, the effect of magnetic storms on scintillation activity will also be presented.

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Magnetic activity effects on ESF irregularities: case studies

D. Tiwari1, B. Kakad1, S. Sripathi1, T. K. Pant2, and A. Bhattacharyya1

1. Indian Institute of Geomagnetism, New Panvel, Navi Mumbai-410 218 ([email protected]) 2. Space Physics Laboratory, VSSC, Trivandrum-695022.

A better understanding of the climatology of Equatorial Spread F (ESF) occurrence versus geomagnetic activity levels is an essential pre-requisite for developing good forecast models. In this context, the present study present an investigation into the evolution of ESF irregularities in the equatorial and low-latitude ionosphere under different ambient conditions in the Indian longitude sector.

Observations of ESF irregularities during magnetically disturbed days during 1998-2004 using spaced receiver VHF scintillations at Tirunelveli (8.70 N, 77.80 E, Dip latitude 0.60 N) and estimated



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parameters zonal drift Vo of the diffraction pattern on the ground, random velocity Vc, which is a measure of the random changes in the irregularity characteristics and maximum cross-correlation CI have been used to investigate the day-to-day variability in the occurrence and duration of ESF and their association with Ionosonde measured parameters (h’F, foF2 and blanketing Es etc) from Trivandrum (8.50 N, 770 E, Dip latitude 0.50 N).

We have used solar wind plasma and magnetic field measurements from the SWEPAM and MAG instruments on board the ACE satellite to investigate the effect of solar wind-magnetosphere-ionosphere coupling on the generation of ESF irregularities. An attempt has also been made to investigate the role of time dependent (i) prompt penetration magnetospheric electric field and (ii) disturbance dynamo and their association with ESF irregularities in the Indian longitude sector. Geomagnetic indices, Kp, SYM-H and ASY-H have been used as indicators of the level of geomagnetic activity.

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Neutral and Plasma variability in the F region from the dissipation of gravity waves from convection

S. Vadas1 and H. Liu2

1: NorthWest Research Associates, CoRA division, Boulder, Colorado, USA ([email protected]) 2: High Alt. Obs, NCAR, Boulder, Colorado, USA

I will discuss the properties of temporally and spatially dependent horizontal body forces in the thermosphere. These body forces arise from the dissipation of convectively-generated gravity waves near the bottomside of the F layer in the thermosphere, and are modeled via convective modeling and ray tracing with dissipative filtering. I will show that these body forces are very common, occurring whenever strong convection occurs, and are directed along the direction the gravity waves were propagating prior to dissipating. I will discuss the neutral and plasma responses to these body forces using theory and new results from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). I will show that these body forces generate strong, localized neutral winds, travelling ionospheric disturbances (TIDs), and other plasma disturbances, thereby creating strong variability near the bottomside of the F region.

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Temporal and spatial regularities in the post-sunset equatorial anomaly, and their significance to scintillation

J.A. Whalen

Woodville Associates, Woodville, Massachusetts, USA ([email protected]

The previous paper demonstrated that the maximum scintillation that could occur in the event of a bubble was a linear function of the F layer maximum electron density. Although bubbles cannot be predicted, if NmF2 could be, an upper limit could be put on S4. There are two areas where such a prediction may be possible, the first temporal, and the second spatial. In the temporal area, previous work has found NmF2 at its post-sunset maximum to show quasi-periodicity of about 3 days for a duration of nearly 90 days. What defined the periods were not the maxima, but the minima. In addition the minima were relative in nature, not of a definable magnitude. However, because the maximum to minimum ratios throughout at were at least a factor of 2 and as great as a factor of 7, NmF2 and therefore S4 could be expected to be a minimum



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by at least such factors at 3 day intervals. The spatial case measures the dependence of maximum NmF2 on solar flux throughout an entire solar cycle using a worldwide array of ionospheric sounders. The dependence near the nominal anomaly maximum was shown previously to increase linearly with solar flux. Here, for latitudes below about 14o dip latitude, NmF2 increases to a maximum, then decreases as solar flux increases. As a result NmF2 is limited to a maximum value. In addition, this maximum increases linearly with latitude. Therefore because of the linear dependence of S4max on NmF2 described in the previous paper, S4 has an upper limit that also increases with latitude over this region.


Session S7: Ionospheric electrodynamics: Theory and numerical modeling

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Do electric fields drive ionospheric plasma flows?

V. Vasyliūnas1 and P. Song2

1: Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany ([email protected]) 2: Center for Atmospheric Research and Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts, Lowell, MA, USA

A widespread assumption in ionospheric electrodynamics is that an electric field perpendicular to the magnetic field produces a bulk flow of the plasma, by imposing an E x B drift on electrons and ions. It has been demonstrated, however, that, as long as the Alfvén speed is much less than the speed of light, an imposed electric field does not produce a plasma flow but dissolves into fluctuations (on a time scale of the electron plasma period), whereas an imposed plasma flow does produce a –V x B electric field; the electric field must therefore be regarded as a consequence of the plasma flow, not its cause. Although the mathematical relation between V and E is not directly affected, this change of viewpoint is important because it brings out the hitherto ignored question of what are the stresses that actually produce the flow. As a particularly clear example, the so-called “storm-time penetration electric fields” are observed as time-varying vertical flows of plasma at the magnetic equator, closely associated with variations of the solar wind and the interplanetary magnetic field; to change the vertical flow velocity and to lift the plasma against gravity, appropriate vertical forces must be exerted. Changes (in response to the solar wind) of magnetospheric convection flow on closed field lines are effected by fast-mode MHD waves, which propagate, in two simplest models, either (1) from the polar cap toward the equator, at low altitudes within and just above the ionosphere, or (2) from the magnetopause inward toward the ionosphere, in the equatorial region of the magnetosphere; in both models, the required vertical force can be produced on inclined field lines.

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Electrodynamics of the thermosphere-ionosphere-magnetosphere system

J. D. Huba

Plasma Physics Division, Naval Research Laboratory, Washington, DC ([email protected])

The electrodynamics of the equatorial ionosphere plays a major role in the transport and temporal evolution of the ionospheric plasma. The dominant drivers for the ionosphere electric field are both internal (e.g., neutral winds) and external (e.g., coupling to the solar wind/magnetosphere system). A self-consistent description of this process involves a coupled model of the thermosphere-ionosphere-magnetosphere system. We will describe the basic physics of this system and provide examples based on TIMECGM (thermosphere model), SAMI3 (ionosphere model), RCM (inner magnetosphere model), and LFM (outer magnetosphere model). Quiet-time and storm-time behavior will be discussed with an emphasis on storm-time dynamo and penetration field effects. Comparison between model results and data will be presented. Research supported by ONR and NASA.



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Approaches to the study of non-electrodynamical sources of ionospheric variability at equatorial and low latitudes

M. Mendillo1, H. Rishbeth1,2, R. Roble3, J. Wroten1, and B. Foster3

1: Boston University, Boston, MA 02215, USA ([email protected]) 2: University of Southampton, Southampton, UK 3: National Center for Atmospheric Research, Boulder, CO, USA

Over the span of the full set of ISEA meetings, participant attention has most often been focused upon topics of plasma disturbances---morphologies, sources, mechanisms and effects. These included both F-layer and E-layer perturbations that range from small scale, non-storm-time, plasma instabilities, to the large-scale modification of the entire ionosphere’s total electron content (TEC) during major geomagnetic storms. Consistent with the very nature of the regime defined by the equatorial ionization anomaly (EIA), electrodynamical processes are often seen to be the foremost driver of disturbed behavior. In addition to locally-induced electric field effects, well known magnetosphere-ionosphere interactions penetrate to low latitudes as well. Attention is now being given to the important sources of vertical coupling from below and, in particular, to non-electrodynamical mechanisms, or at least processes initiated by non-electrical effects. In this paper, we review the broad context of ionospheric variability over time scales of day-to-night, day-to-day and month-to-month. We do this using the TIME-GCM model run for each day of 2002, and compare the predictions for variability with the patterns observed at three low latitude ionosonde stations. These are Jicamarca (near the geomagnetic equator), Ascension Island (near a crest of the EIA), and Darwin (poleward of the EIA). As with midlatitude effects, observed variability for the F-layer peak density is typically 15-25% for all seasons, while model results fall short of that level. Variabilities observed during geomagnetic disturbances versus quiet periods do not differ appreciably, as found also in model calculations using input parameters for each of those days.

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Redistribution of the low-latitude ionospheric plasma structure during a major magnetic storm

C. H. Lin1, A. D. Richmond2, G. J. Bailey3, and J. Y. Liu4

1: Plasma and Space Sciences Center, National Cheng-Kung University, Tainan, Taiwan ([email protected]) 2: High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA 3: Department of Applied Mathematics, University of Sheffield, Sheffield, S3 7RH, UK 4: Institute of Space Science, National Central University, Chung-Li, Taiwan

This study presents theoretical simulation of the mid- and low-latitude ionospheric electron density structures during a major magnetic storm. From the coupled NCAR Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and Sheffield University Plasmasphere Ionosphere Model (SUPIM) simulation runs, storm-generated ionospheric additional layers (named as F3 or F1.5 layer or G condition) occur in both equatorial and low-latitude ionospheric regions due to two different physical mechanisms. The additional layer occurred at the equatorial region is formed due to a strong uplift of the original F2 layer results from an eastward penetration electric field, and followed by replenishment of the newly produced ionization located at the original F2 layer height. This process requires existence of the sunlight in order to produce fresh plasma through photo-ionization process. On the other hand, the additional layer formed at low-latitude requires the existence of the storm-generated equatorward wind.



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The storm-generated equatorward wind slows down the downward diffusion of plasma at the equatorial ionization anomaly (EIA) crests. The equatorward wind acts like a funnel letting the plasma at EIA crests drip down to a lower altitude and form a new layer there. The presented results indicates that the ionospheric additional layers may occur in both low-latitude and equatorial regions during magnetic storm periods if preferable storm-generated conditions exist. Meanwhile, the model runs also predict the ionospheric electron density hole, electron density trough, electron density arches during the magnetic storm. The storm-time electron density hole is produced by the same process as the additional layer formed at the magnetic equator. On the other hand, if the F-layer uplift occurred during evening hours, while the photo-ionization process becomes much weaker, an equatorial density trough is then formed. The electron density arches are signature of the downward diffusion of the uplifted plasma at the magnetic equator. These model predictions are also compared with the observations.

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Low latitude storm time electric fields and its role in the coupled thermosphere-ionosphere-plasmasphere system

N. Maruyama1, T. Fuller-Rowell1, M. Codrescu1, D. Anderson1, A. Richmond2, A. Maute2, S. Sazykin3, F. Toffoletto3, R. Spiro3, R. Wolf3, and G. Millward4

1: University of Colorado, CIRES, and NOAA, SWPC, Colorado, USA ([email protected]) 2: National Center for Atmospheric Research, High Altitude Observatory, Colorado, USA 3: Rice University, Physics and Astronomy Department, Texas, USA 4: University of Colorado, LASP, Colorado, USA

We have developed a self-consistent first-principles model of the inner magnetosphere and thermosphere-ionosphere-plasmasphere, in order to understand the response of the electrodynamic interactions within the coupled system and the role of the electrodynamics in restructuring the ionosphere, plasmasphere and thermosphere, in particular, during geomagnetically active conditions. Modeling of the storm-time ionospheric electrodynamics requires a description of the two disturbance mechanisms: prompt penetration and disturbance dynamo. We have coupled the Rice Convection Model (RCM), used to calculate the region 2 field aligned currents from the inner magnetosphere which control the shielding process of the high latitude convection electric field, and the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, used to calculate the time-dependent conductivities and neutral winds that are the key to describe the disturbance dynamo as well as the quiet-time ionospheric wind dynamo. Self-consistency in the electrodynamic coupling between RCM and CTIPe is accomplished by using a common global electrodynamic solver. As compared to the classical picture of prompt penetration, our model results from the non self-consistent coupling suggest a possibility that penetration effects can have a longer lifetime when the IMF Bz is large and southward, as a consequence of the ineffective shielding resulted from the magnetospheric reconfiguration. Furthermore, our simulations indicate that the arrival of the disturbance dynamo effect in the low latitude ionosphere can possibly be faster than previously believed, as the disturbance dynamo is modified by the changes in the conductivity and neutral wind initiated by the penetration effect. Comparison of the results from the combined models with observations under a variety of conditions demonstrates that our models are capable of reproducing many of the observed features in the ionosphere. In this paper, the electrodynamic interactions will be discussed using the fully self-consistently coupled model, and its impact on the low latitude coupled ionosphere- thermosphere system.



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Ionosphere electrodynamics and its influence on the equatorial anomalies

M. V. Klimenko1, V. V. Klimenko2, and V. V. Bryukhanov1

1: Kaliningrad State Technical University, Kaliningrad, Russia ([email protected]) 2: West Department of N.V. Pushkov Institute of Terrestrial Magnetizm, Ionosphere and Radio Wave Propagation (IZMIRAN) of Russian Academy of Science, Kaliningrad, Russia

In the given work the numerical simulation results of global distributions of the zonal current in the Earth’s ionosphere and the critical frequency of the F2-layer of the ionosphere are presented. The calculations are executed with use of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in West Department of IZMIRAN and added by the new block of calculation of the electric field of the dynamo and magnetospheric origin. The calculations are executed for quiet geomagnetic conditions during various seasons and levels of Solar activity without taking into account the electric field, and also with taking into account only dynamo-field or superposition of a dynamo-field and magnetospheric convection field with and without taking into account the shielding by field aligned currents of the second zone. It is shown, that Equatorial Ionization Anomaly is not formed in the absence of the electric field. The main part in formation of Equatorial Ionization Anomaly plays a dynamo-field. Zonal component of dynamo-field together with diffusion of thermal plasma along geomagnetic field lines under action of the pressure gradients in the Earth’s gravity field cause a fountain effect at geomagnetic equator. We have considered the influence of the ionospheric electrodynamics on the formation and development of Equatorial Plasma Temperature Anomaly. Equatorial Electrojet is formed by the dynamo-field. Magnetospheric convection at presence of shielding weakly influences on behavior of Equatorial Electrojet. Without the shielding of magnetospheric convection electric field by Alfven layer electric field the magnetospheric convection influence on Equatorial Electrojet becomes stronger. It occurs during magnetospheric disturbances when the shielding is broken due to fast changes of the field aligned currents of the first zone. There are presented the seasonal, Solar-cyclic and UT-variations of Equatorial Electrojet and equatorial anomalies.

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Observations and model calculations of stratification of the F2 layer in the equatorial ionosphere

J. Uemoto1, T. Ono1, T. Maruyama2, S. Saito2, M. Iizima1, and A. Kumamoto1

1: Tohoku University, Sendai, Japan ([email protected]) 2: National Institute of Information and Communications Technology, Tokyo, Japan

In this paper, we focused on stratification of the F2 layer in the equatorial region which is strongly concerned with the interaction between the ionospheric plasma and the thermospheric neutral gases. Studies on stratification of the F2 layer have a long history, and this stratification has been individually observed from the ground and from the topside ionosphere as the F3 layer and as the ionization ledge, respectively. However, the relationship between the two has not been clarified, and some unexplained problems still remain for each phenomenon. In order to clarify the structure and dynamics of the F3 layer and the ionization ledge and the relationship between the two, we analysed the bottom side sounder data obtained from the SEALION and the topside sounder data obtained from the Ohzora and ISIS-2 satellites, and performed model calculations using the SAMI2 code.



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As a result of the model calculation and the SEALION data analysis, the mechanism of the F3 layer was suggested as follows: The F3 layer corresponds to the density enhanced region associated with the equatorial anomaly. This enhanced region moves upward and to a higher latitude region due to the E × B drift and the field aligned diffusion. When it reaches the altitude sufficiently separated by the F2 layer at a lower altitude, the plasma density enhanced region becomes observable from the ground as the F3 layer. The density enhanced region continues to move to a higher altitude and a higher altitude latitude region, so that the F3 layer is shifted to a latitude region. The meridional neutral wind moves the density enhanced region at a higher altitude region in the windward hemisphere and at a lower altitude region in the leeward hemisphere. As a result, the formation of the F3 layer is promoted in the windward hemisphere and suppressed in the leeward region by the meridional neutral wind.

On the other hand, as a result of the model calculation and the topside sounder data analysis, the mechanism of the ionization ledge was suggested as follows: The plasma density enhanced flux tube was generated through the photo-chemical process at the altitude just above the F2 peak over the magnetic equator in the early morning local time. This flux tube rises upward by the E × B drift. When the altitude of this flux tube is sufficiently separated by the F2 layer (highest density peak) at a lower altitude, the ionization ledge becomes observable from the topside ionosphere. The ledge field line becomes separated from the magnetic field line passing through the equatorial anomaly crest during the night local time due to the faster loss of plasma in the equatorial anomaly crest at the higher latitude. Since the plasma density structure becomes asymmetrical by the meridional neutral wind, the meridional neutral wind suppresses the formation of the density enhanced region at a high altitude. Then, the formation of the ionization ledge is suppressed by the meridional neutral wind.

The dynamics of these phenomena can be understood in the two dimensional frame of the whole magnetic meridional plane connected by the magnetic field lines. Based on the different mechanisms of each phenomenon, it is concluded that it is not necessary for the ionization ledge to accompany the F3 layer.

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F3 layer during penetration electric field

N. Balan1, H. Alleyne1, S. V. Thampi2, K. Lynn3, Y. Otsuka4, B. G. Fejer5, and M. A. Abdu6

1: University of Sheffield, S1 3JD, UK ([email protected]) 2: Vikram Sarabhai Space Centre, Trivandrum, India 3: Ionospheric Systems Research, Noosaville QLD 4566, Australia 4: Nagoya University, Toyakawa, Japan 5: Utah State University, Utha, USA 6: DAE, INPE, Brazil

The occurrence of an additional layer, called F3 layer, in the equatorial ionosphere at American, Indian and Australian longitudes during the super double geomagnetic storm of 07-11 November 2004 are presented using observations and modeling. The available observations show the occurrence, reoccurrence and quick ascent to the topside ionosphere of unusually strong F3 layer in Australian longitude during the first and second super storms (08 and 10 November) and in Indian longitude during the second super storm (10 November), all with large simultaneous reductions in peak electron density (Nmax) and total electron content (GPS-TEC); the F3 layer also occurred in Australian longitude on the comparatively less active day (09 November) though of a different character. The modeling studies conducted using the Sheffield University Plasmasphere Ionosphere Model (SUPIM) indicate that the unusual F3 layers during



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the super storms might have been caused mainly by unusually large double peaked equatorial upward ExB drift (or eastward electric field). The indication is supported by the simultaneous observations of the strongest daytime eastward prompt penetration electric field (PPEF) ever recorded (at Jicamarca) and large depletions in Nmax (at Jicamarca and Sau Luis) at American longitude; the depletions are also modeled by incorporating the PPEF. The large depletions in Nmax that occurred during the afternoon-evening hours (14-17 LT) are also followed by unexpected unusally large increases in Nmax (greater than daytime Nmax) during the following evening hours (17-23 LT) due to the large downward ExB drift or reverse plasma fountain.

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Modeling low-latitude ionosphere using GAIM assimilating GPS data

X. Pi, V. Akopian, A. Komjathy, B. D. Wilson, A. J. Mannucci, B. A. Ijima, and M. A. Dumett

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Assimilative ionospheric modeling is a developing technique that images ionospheric weather by assimilating observations into physics-based numerical models. Studies are conducted for modeling the weather of low-latitude ionospheric dynamics and electron densities using the JPL/USC global assimilative ionospheric model (GAIM). Our purpose is to investigate the effectiveness of estimating the variability of multiple model drivers, and imaging the ionospheric state, by assimilating GPS data into GAIM and applying four-dimensional variational (4DVAR) and Kalman filter (KF) approaches. The targeted drivers include the zonal electric field and magnetic meridional wind simultaneously for all longitudes, as well as solar EUV flux. The GPS data include both ground-based and space-borne occultation measurements, the latter made using GPS receivers on board low-Earth orbiters including 6 COSMIC satellites. In the assimilative modeling, minimization of the difference between the modeled state and observations is attempted by either adjusting the model drivers or through recursive filtering. In this presentation, we will describe 4DVAR observation system simulation experiments (OSSEs) conducted recently based on realistic GPS observation distributions, and show the KF modeling results of electron density profiles compared to incoherent scatter radar measurements made at low latitudes. The potential impact of such assimilative modeling on equatorial aeronomy research and applications will also be discussed.

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Assimilation of ROCSAT equatorial electric field data into the AFRL C/NOFS model

M. C. Kelley1, J. Retterer2, O. de La Beaujardière2, and H. Kil3

1: Cornell University, Ithaca, NY, USA ([email protected]) 2: Air Force Research Laboratory, Hanscom AFB, MA, USA 3: Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

A key parameter to be assimilated into the Air Force effort to predict convective equatorial ionospheric storms is the electric field measured on the associated satellite. As a precursor to this era, the interplanetary electric field has been successfully used to predict conditions an hour ahead (Kelley and Retterer, Space Weather Quarterly, 2008). Here we report on the use of ROCSAT equatorial electric field data to drive the model and compare the results to a number of other observations, including satellite



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airglow data such as GUVI and tidal models. In addition, we compare the linear growth rate predictions of the model against longitudinal and seasonal characteristics of convective equatorial ionospheric storms.

Estimating electric fields in the equatorial ionosphere from CHAMP observations

P. Alken1 and S. Maus2

1: University of Colorado, Boulder, Colorado, USA ([email protected]) 2: National Geophysical Data Center, NOAA, Boulder, Colorado, USA

The CHAMP satellite, launched in July 2000, provides more than 7 years of ionospheric magnetic measurements at low altitudes. The Equatorial Electrojet (EEJ) produces a strong signal in these magnetic measurements, which have been inverted for high-quality meridional current profiles. These profiles contain key information on the eastward electric field which drives the current system. By solving the governing differential equation for each of over 40,000 CHAMP equator crossings, we have produced estimates of the eastward electric field with global coverage. These estimates have been found to be consistent with ground based measurements at the JULIA radar at Jicamarca, Peru. The resulting data set provides valuable new information on the longitudinal, seasonal and local time structure of the day side eastward electric field.

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Quantifying the daytime, equatorial ExB drift velocities associated with the 4-cell, non-migrating tidal structure

D. Anderson1, E. Araujo - Pradere1, A. Anghel1, K. Yumoto2, A. Bhattacharyya3, M. Hagan4, A. Maute4, and L. Scherliess5

1: University of Colorado/CIRES, Boulder, Colorado ([email protected])

2: Space Environment Research Center, Kyushu University, Japan 3: Indian Institute of Geomagnetism, Mumbai, India 4: High Altitude Observatory, NCAR, Boulder, Colorado 5: Center for Atmospheric and Space Sciences, Utah State University, Logan

In the daytime, equatorial ionosphere, the vertical ExB drift velocity is the major transport mechanism for creating crests in ionization on either side of the magnetic equator at +/- 15o to 18o dip latitude known as the equatorial anomaly. There is a large, day-to-day variability in these drift velocities due to tidal forcing from below, penetration of high latitude electric fields and disturbance dynamo generated electric fields. In this paper, we investigate the seasonal and longitude dependence of the daytime, vertical ExB drift velocities, on a day-to-day basis, using a recently-developed technique for inferring realistic ExB drifts from ground-based magnetometer observations. We have chosen only quiet days, Ap<10, from January, 2001 through December, 2002, so that the main contribution to the variability is due to the variability in the tidal forcing from below. In order to study the longitude dependence in daytime ExB drift velocities, we use appropriately-placed magnetometers in the Peruvian, Indian and Philippine sectors. To study the seasonal variability we have binned all of the quiet day observations in 2 month bins, e.g. January-February, March-April…..November-December for both 2001 and 2002. Since we are particularly interested in quantifying the ExB drift velocities associated with the 4-cell, non-migrating tidal structure, we compare the seasonal and longitude ExB drift structure with recent satellite observations of neutral temperature and neutral winds that signify tidal forcing as well as satellite observations of daytime ExB



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drift velocities. In addition, we compare the ExB drifts with recent theoretically-calculated, daytime values in the Peruvian, Indian and Philippine longitude sectors. As an example, we find that the maximum, average ExB drift velocity for the March-April, 2002 time period, which corresponds to the IMAGE FUV observations of the 4-cell pattern, is 26 m/sec in the Peruvian sector; 22 m/sec in the Indian sector and 23 m/sec in the Philippine sector. From the IMAGE observations, one of the four maxima in the 135.6 nm radiances occurred in the Peruvian sector and two of the four minima occurred in the Indian and Philippine sectors, respectively. Implications of the season and longitudinal dependences in ExB drift velocities to tidal forcing will be discussed.

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Diurnal, seasonal and solar cycle variations of the longitudinal wavenumber-4 patternsat low latitude ionosphere

W. Wan, J. Xiong, L. Liu, M.-L. Zhang, F. Ding, and B. Ning

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, P. R. China ([email protected])

The data of total electron content (TEC) from the JPL global ionospheric maps (GIMs) are used to investigate the longitudinal structure of the equatorial ionospheric anomaly (EIA). As a proxy of EIA parameter, the latitudinal integration of TEC (ITEC) is first extracted from low latitude GIMs and then Fourier filtered to obtain the wavenumber-4 components. We then study in detail the diurnal, seasonal and solar cycle variations of the wave patterns. It is found that the wavenumber-4 patterns changes pronouncedly with seasons and slightly with solar activity. They are intense and well developed in boreal summer and early boreal autumn, but quite weak in boreal winter; it increased in boreal spring and decreased rapidly in later boreal autumn. This seasonal variation is consistent with that of the zonal wind and temperature of the non-migrating tide mode DE3 detected by SABER and TIDE observation. We also found that the wavenumber-4 patterns shift eastward with shifting speed smaller in daytime and larger at night. This is attributed to the contribution of both the eastward propagation of DE3 in E-region and the zonal E×B ion drifts in F-region. The derived zonal drift speed is coincident in seasonal and solar cycle variation with the observation of upward electric field. Our results support the suggestion that the longitudinal wavenumber-4 structure of EIA should be originated from the non-migrating tide mode DE3 in ionospheric E-region and affected by the E×B ion drifts in F-region.

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Model simulation of longitudinal density structure in the equatorial ionosphere

T. W. Fang1, 2, A. D. Richmond1, H. Kil3, G. Millward4, and J. Y. Liu2

1: High Altitude Observatory, National Center for Atmospheric Research, USA 2: Institute of Space Science, National Central University, Taiwan 3: Johns Hopkins University, Applied Physics Laboratory, USA 4: Laboratory for Atmospheric and Space Physics, Univ. of Colorado, USA

The four-peaked density structure in the equatorial ionization anomaly (EIA) region has been confirmed by many satellite observations. The drift velocities above the magnetic equator observed by Rocsat-1 clearly showed a longitudinal structure in the daytime period with longitudinal peaks similar to the



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daytime and evening EIA structures. It is believed that the daytime vertical drifts in the equatorial region are controlled by the wind dynamo, which is modulated by atmospheric tides in the E region. In order to understand how the vertical drifts relate to the longitudinal structure of the EIA, we conduct model simulations using the Global Ionosphere and Plasmasphere (GIP) model. The GIP model uses a realistic magnetic field, a neutral wind from HWM-07, and thermospheric parameters from the NRLMSISE-00 model. Applying the equatorial vertical drifts of Rocsat-1, the model well reproduces the longitudinal structure of NmF2 in the EIA region. It shows that the structure is most pronounced in equinox and appears in both daytime and nighttime. In this paper, the time evolution and seasonal variation of the longitudinal density structure will be presented, and comparison between the model density and satellite observations (ROCSAT-1, DMSP, COSMIC and GUVI) will be shown. In addition, we examine the importance of the pre-reversal enhancement in the vertical drift and of the neutral wind in changing the electron density structure after sunset. First, we make changes in the magnitudes of the drifts in the daytime and near sunset to see the responses of nighttime electron density. Secondly, we investigate the possibility that the meridional wind enhances or diminishes the nighttime four-peaked structure. Using the GIP model helps us to better understand the mechanisms causing the longitudinal structure.

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The effect of the daytime ExB drift, interhemispheric winds, and pre-reversal enhancement on the formation of longitudinal density structure

H. Kil1, S. –J. Oh2, and L. J. Paxton1

1: Johns Hopkins University Applied Physics Laboratory ([email protected], [email protected]) 2: Space Environment Laboratory, Seoul, Korea ([email protected])

We will conduct SAMI2 model simulations to investigate the dependence of the F-region density structure on the input vertical ExB drift model. While the presence of the longitudinal variation in the density structure in the low-latitude F region is well known, no model has the capability to reproduce the observed longitudinal density structure of the EIA without introducing either an ad hoc forcing at the lower boundary or an ExB drift pattern that varies with longitude as well as local solar time. ROCSAT-1 provides the most reliable plasma drift data on the topside and the observed ionospheric density structure shows an excellent correlation with the ROCSAT-1 ExB drift pattern. The empirical ExB drift model developed by Scherliess and Fejer has been widely used as an input to the low-latitude ionospheric models including the SAMI2 model. We will investigate the difference of the model ionospheres produced by using the conventional empirical ExB drift model and the newly derived ROCSAT-1 ExB drift model. We will also investigate the effect of neutral wind and evening pre-reversal enhancement on the modification of the nighttime wave structure.



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Search for magnetic inclination effects at low latitude in the spectral resonance structures of the ionospheric Alfvén resonator

T. Bösinger1, E. N. Ermakova2, and C. Haldoupis3

1: University of Oulu, Oulu, Finland ([email protected]) 2: Radio Physical Research Institute (NIRFI), Nizhny Novgorod 3: University of Crete, Heraklion, Greece

From May 1999 till February 2006 the University of Oulu in cooperation with the University of Crete operated a pulsation magnetometer at the island of Crete in order to survey the electromagnetic background noise caused by world-wide lightning activity. This in Europe southernmost observation point (geographic latitude ~35o North) let to the discovery of signatures in the spectral resonance structure (SRS) of the ionospheric Alfvén resonator (IAR) well distinct form similar high latitude observations. This report is a continuation of this work stimulated by recent numerical simulation on magnetic inclination effects (~50o). They include 1) SRS can be detected in both orthogonal components, 2) the harmonics in SRS are not necessarily equidistant, 3) SRS may exhibit different frequency scales in the two orthogonal components. Our data survey is a first attempt to verify such predictions. It is not as straight forward because the predicted effects do not depend only on the magnetic inclination angle but also on the angle of the wave vector of the lightning induced electromagnetic wave forming with the magnetic meridian passing through the observation site. Due to lightning-activity going on in different locations world-wide this latter angle is not well defined.


Session S8: Coupling processes at low- and mid-latitudes

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Response of the low-latitude ionosphere-thermosphere system to high-latitude activity

Hermann Lühr and Patricia Ritter

GeoForschungsZentrum Potsdam, Potsdam (hLü[email protected])

The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere, thermosphere. There are, however, several mechanisms which channel part of the disturbances to low and mid latitudes. Some of these mechanisms cause a prompt response, for example, the penetration electric field. Other processes require hours before the perturbation has reached the equator (e.g. travelling atmospheric disturbances).

Here we will present some recent observations primarily derived from the CHAMP satellite. With its sensitive accelerometer it can measure the air density and zonal winds. During magnetic storms the thermospheric density is enhanced first at high latitudes and some hours later the bulge reaches the equator. The response time is shorter on the dayside than on the night side. None of these thermospheric responses to magnetospheric inputs are reproduced well by present-day atmospheric models.

Another topic to be addressed will be the low latitude ionosphere/thermosphere response to substorm onsets. Based on a large number of substorm events the average response to this kind of disturbance was deduced. We compare ground-based and satellite observations. This allows us to distinguish between ionospheric and magnetospheric currents. There is increasing evidence for significant ionospheric currents even during the night. As a consequence of that many of the interpretations based solely on observatory data from the night side have to be reconsidered.

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Variations of thermospheric [O] composition during a magnetic storm event

R. Hedden1, L. Waldrop2, and J. Meriwether1

1. Clemson University, Clemson, SC ([email protected]) 2. University of Illinois, Urbana-Champaign, IL

Morning and evening twilight high-resolution imaging Fabry-Perot measure-ments of the 732-nm O+ thermospheric emission line shape were obtained during the early part of September when an intense magnetic storm took place. The location of these observations was at Arequipa, Peru (16.2 S, 71.5 W). These observations were analyzed to remove the OH contamination that was also seen in these spectra. The relative intensity of the O+ emission twilight variation was plotted as a function of the solar depression angle and these plots were compared with the GLOW model predictions. Reasonable agreement based upon the MSIS model [O] density was found for data obtained during quiet periods. During the period of the storm activity the results showed a discrepancy that could not be explained by a decrease of the thermospheric oxygen composition. It is suggested that the increased thermospheric heating caused by the storm increased the molecular quenching that takes place in early twilight when the shadow height is near 200 km thus decreasing the observed 732 nm. In later twilight the shadow height is much higher where the increased EUV illumination would increase the 732 nm emission observed; at these altitudes there is no significant quenching. The overall effect during the storm period would be a flatter twilight profile which is the effect observed.



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New results on equatorial thermospheric dynamics and the midnight temperature maximum

J. Meriwether1, M. Faivre1, C. Fesen1, and O. Veliz2

1: Clemson University, Clemson, SC ([email protected]) 2: Radio Observatorio Jicamarca, Lima, Peru

Fabry-Perot observations of the Doppler shift and Doppler broadening of the equatorial 630 nm OI nightglow were made in 2005 and 2006 at Arequipa, Peru (16.2 °S, 74° W) to study the coupling of the thermospheric tide to the formation of the midnight temperature maximum. The Arequipa imaging Fabry-Perot interferometer utilized a new observing strategy in which 630-nm line-of-sight measurements were obtained for eight directions at azimuthal intervals of 45 ° from 0 to 360° at 60° zenith angle to determine the mean zonal and meridional winds. Utilizing the assumption that the zonal derivative may be replaced by a local time deriviative, estimates of the divergence and vorticity of the neutral wind flow were obtained to construct a map of the thermospheric wind field. These results showed that the midnight temperature maximum (MTM), typically seen with an amplitude ranging from 75 K to 200 K, was always observed when 60 to 90 minutes prior to the MTM peak there was seen an equatorial meridional wind flow of 50 to 100 ms-1. When there was no significant flow in the equatorward direction, the MTM amplitude was weak. The results are interpreted to indicate the meridional flow is caused by the semi-diurnal tidal mode with the possibility of a contribution also by the terdiurnal tidal component. Calculations of the expected nighttime temperature structure with the NCAR ionosphere-electrodynamics thermosphere general circulation model produced no significant MTM events for the three nights selected for modelling. The lack of any success is interpreted to mean that the terdiurnal tidal mode needs to be included as part of the E-region tidal forcing.

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Simulations of the midnight temperature maximum with the NCAR TIME-GCM

C. G. Fesen1, R. G. Roble2, and H. Liu2

1: Clemson University, Clemson, South Carolina, USA ([email protected]) 2: High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA

The midnight temperature maximum is a common feature in the nighttime low latitude thermosphere which has been observed since the 1970’s with both ground-based and space-based instruments. As the name implies, the feature is distinguished as a local maximum in the neutral or ion temperatures that occurs within a few hours of local midnight. The amplitude is highly variable, ranging from a few tens to a few hundred degrees. Satellite observations have established a climatology marked by strong seasonal and latitudinal variations: larger amplitudes occur during equinoxes and are roughly centered on the equator. During solstices, the peak occurs off the equator and is larger in summer than winter, developing before midnight in the summer and after midnight in the winter. Theoretical modelling of the midnight temperature maximum has thus far been generally unsatisfactory: simulated amplitudes are typically substantially smaller than those observed. Recently, the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamic general circulation model (TIME-GCM) has incorporated an option to employ a finer grid resolution in the horizontal and vertical directions. Simulations for September 2005 with the higher resolution model have produced larger amplitudes for the



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midnight temperature maximum than have been previously obtained. The simulations also exhibit significant longitudinal variability and greater latitudinal variability than the lower resolution model.

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Equatorial mesospheric planetary wave wignatures in the equatorial electrojet

T. K. Ramkumar

National Atmospheric Research Laboratory, PB No. 123, Tirupati-517502, India ([email protected], [email protected])

Detailed investigations have been made on the possible influences of mesospheric planetary waves on the equatorial electrojet using collocated measurements of equatorial mesospheric and lower thermospheric region horizontal winds with MF radar and geomagnetic field in the Indian dip equatorial region during the solar minimum year of 1995. It is noted in meridional wind that few cycles (burst like) of ~ 2-day oscillation occurred intermittently in all the seasons of the year 1995. In EEJ strength, however, oscillations with weak amplitude are found only in the late summer months of July and August and significant amplitude in the first 10 days of October. Further, during the late summer months of July-September and the winter month of November, the zonal wind shows prominent spectral power for a wide spectrum of periodicities near 3, 5, and 6.5 days. In the latter two months, the zonal wind shows significant power also near the periodicity of 10 days. In the case of EEJ strength, only August and October are favorable to show the enhanced amplitudes of oscillations near the periodicities of 5 and 6.5 days. Furthermore, while the meridional wind shows significant ~ 10-day oscillation in the winter months of February and November-December, the EEJ strength shows weak wave signature only in February. And the ~ 6-8 day oscillation found in zonal wind in the summer months of April and May is not accompanied by similar enhancements in EEJ strength.

For long period wave oscillations, a good correlation between ~ 14-day oscillation in meridional winds and EEJ strength occurs during the winter and summer months of January and June respectively. The zonal wind, however, shows significant spectral power near the periodicity of 19 days. Further, during the spring equinox month of April,when the EEJ strength shows strong spectral power near the periodicity of 15 days, the zonal wind shows significant power near the periodicity of 20 days. Moreover, during the late summer month of August and the winter month of October, the EEJ strength shows enhanced spectral power near the periodicity of 15 days. In the case of winds, however, the meridional component shows but less significant power in the periodicity range of 14-20 days in August. And the zonal wind shows strong spectral power in the periodicity range of 15-20 days from mid-October to full November. It is to be recalled that some times the two strong sources of high-energy solar radiations located almost 180º apart on solar longitudes may modulate the E region ionization near the periodicity of 14 days. This is due to the average 27-day rotational period of the sun in the equatorial region. This ~ 14-day variation in ionization of E region would be observed as ~ 14-day oscillation in ionospheric parameters. Investigations are being made that what actually causes sometimes and not sometimes the penetration of planetary scale waves from below up to the dynamo E-region and have influences there on the ionospheric current systems, which are manifested in the ground observed geomagnetic field measurements.



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Penetration of gravity waves into the F region from the lower atmosphere at low and mid latitudes

S. Vadas

NorthWest Research Associates, CoRA division, Boulder, Colorado, USA ([email protected])

In this talk, I will discuss the generation, propagation, and dissipation of gravity waves excited by convection at equatorial and mid-latitudes. This talk will be theoretical in nature, and will involve the use of two models, one for the generation of gravity waves by convection, and the other for the ray tracing of gravity waves into the thermosphere through realistic temperatures and winds. The ray trace model now includes gravity wave phases from convection, thereby allowing for the reconstruction of the gravity wave field at any altitude. I will show that because of dissipative filtering in the thermosphere, differing portions of the initial convective spectrum survive to differing altitudes in the thermosphere. I will also show that the background, neutral winds play a key role in establishing the direction of propagation of gravity waves in the thermosphere at the bottomside of the F layer. I will also show that those gravity waves from convection which propagate to the bottomside of the F layer have horizontal scales of 100-400 km. Finally, I will display the amplitudes of the dominant, convectively-generated gravity waves at the bottomside of the F layer.

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Indications of gravity wave scales, amplitudes, and influences in the thermosphere and ionosphere from the Spread F Experiment (SpreadFEx)

D. C. Fritts1 and SpreadFEx colleagues

1: NWRA/Colorado Research Associates, Boulder, CO ([email protected])

The Spread F Experiment (SpreadFEx) was performed in Brazil from September to November 2005. The primarily goal of the experiment was to seek evidence for seeding of ESF and plasma bubbles extending to higher altitudes by gravity waves (GWs) arising from deep tropical convection. Airglow measurements of GWs in the neutral atmosphere, satellite observations and modelling of deep convection, and theoretical assessments of GW propagation and dissipation suggest that GWs may achieve large amplitudes at high altitudes, but only for limited ranges of wavelengths and frequencies. SpreadFEx plasma measurements appear to confirm these estimates of GW scales and amplitudes. Corresponding GW (and tidal) perturbations of electron densities, gradients, electric fields, and differential plasma and neutral drifts appear to be substantial and may contribute appreciably to plasma growth rates and plasma instability scales.

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Equatorial and mid-latitude scintillation initiated from tropical storms, hurricanes, and typhoons

R. L. Bishop and P. Straus

The Aerospace Corporation, El Segundo, CA, USA ([email protected])

Using GPS occultation data from the PicoSat and CHAMP satellites enables a global study of scintillation connected to large tropical storms. This study utilizes GPS occultation (GPSRO) to investigate TEC levels



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and ionospheric scintillation near hurricanes and typhoons. GPSRO measurements from receivers on LEO satellites supply accurate global ionospheric and upper atmospheric monitoring. In this presentation we examine the ionospheric conditions near tropical storms located in the northern and southern hemisphere and at equatorial and mid-latitudes. In the northern hemisphere mid-latitudes our results show that significant scintillation or ionospheric disturbances are observed near storms. Specifically, during Pacific typhoons in 2002-2003, scintillation is present over 70% of the time. We also show and discuss the orientation of scintillation relative to the storms’ center and the influence of geomagnetic activity. An overview of recent equatorial observational and modeling work is presented showing the coupling between the troposphere/ionosphere. We will present specific storm examples occurring at low magnetic latitudes and discuss their affects on the local ionosphere.

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Semidiurnal tidal signature in sporadic E occurrence rates derived from GPS radio occultation measurements at mid-latitudes

C. Arras1, J. Wickert1, C. Jacobi2, S. Heise1 , G. Beyerle1, T. Schmidt1, and M. Rothacher1

1: GeoForschungsZentrum Potsdam, Germany ([email protected]) 2: University of Leipzig, Faculty of Physic and Geosciences, Germany

The GPS radio occultation (RO) technique is used to study sporadic E layer plasma irregularities in the Earth’s ionosphere on a global scale. With the combination of data received onboard the three different RO missions CHAMP, GRACE and COSMIC, our dataset comprises about 2500 globally distributed occultations daily. Sporadic E-layers cause strong fluctuations in radio signals. Therefore the GPS signal-to-noise ratio is well-suited for sporadic E detection. Through the windshear (V x B) mechanism the ionospheric E region interacts with the mesospheric/lower thermospheric neutral wind field. Sporadic E layers are formed in a region of negative zonal wind shear, i.e. with westward winds over eastward winds. It is generally thought that this shear is provided by solar tides, in particular by the semidiurnal tide (SDT). We present sporadic E layer measurements which exhibit a dominating semidiurnal signature, and a decrease with local time as is the case with neutral wind SDT. Comparisons with wind shears measured by the meteor radar at Collm, Germany and the WINDII instrument on UARS show excellent agreement between the phases of sporadic E semidiurnal signal and the SDT phases.

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Neutral wind, sporadic E layer, and F layer coupling in the nighttime mid-latitude ionosphere

Russell Cosgrove

SRI International, Menlo Park, California, USA ([email protected] )

Relative to other regions, the nighttime mid-latitude ionosphere is quiescent. It lacks a dominant plasma instability, and it is not strongly driven by external electric fields. As a result, atmospheric forcing, and coupling between different electrodynamical mechanisms controls the evolution. We describe herein a coupling process wherein atmospheric winds interact with electrodynamical degrees of freedom in sporadic E (Es) layers, and in the F layer, and of how the latter two interact with each other through the mapping of electric fields along magnetic field lines. Simulations of the coupled system are presented.



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Theoretical support is described. In comparison with observations, we discuss the emergence of the larger scale F layer structure, the smaller scale Es layer structure, and of a preferred orientation. The intent is to tie together many of the recent results of observations, of theory, and of simulations.

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Observations of meteor trail diffusion using VHF radar

J. Younger1, I. M. Reid1,2, and R. A. Vincent1

1: Physics, University of Adelaide, Adelaide, Australia ([email protected]) 2: ATRAD Pty Ltd 1/26 Stirling St, Thebarton, SA, Australia

The diffusion of meteor trails has recently been exploited to estimate temperatures in the 80-100 km region of the atmosphere. More recent modelling work has suggested that meteoric dust laid down by the trails themselves will affect the diffusion of the trails. Naturally, this will lead to incorrect temperatures being determined. In this work, we model the diffusion of the trail. We confirm a difference in the diffusion of observed meteor trails when sorted by echo strength for both low and mid-latitude sites and also demonstrate a difference when echoes are sorted by height and by radar frequency. These observational results are in good agreement with our simple model.

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Quasi-Periodic F-region MSTIDs at Arecibo: A magnetospheric link?

J. D. Mathews1, D. Livneh1, I. Seker1, and F. T. Djuth2

1: The Pennsylvania State University, University Park, PA, USA ([email protected]) 2: Geospace Research, Inc., El Segundo, CA 90245, USA

Spatially coherent (MSTID: Medium-Scale, Traveling Ionospheric Disturbances) waves with quasi-periods of ~1-hour have been found to be continuously and ubiquitously present—at least away from solar maximum—in incoherent scatter radar observations of the ionosphere over Arecibo Observatory (AO) in Puerto Rico [Livneh et al., 2007]. The same or very similar MSTID phenomenon has also been detected using the ISRs at Millstone Hill and Poker Flat AK. In all cases the waves are observed to be nearly continuously present over multi-day geomagnetically quiet to moderately active observation periods. The radar data sets are filtered to highlight the waves although they are visible in unfiltered Arecibo power profile results. The AO radar results show the waves strongly throughout the F-region, often spanning 160 km to above 750 km in altitude. The waves are detected day and night in the F2-layer. Nighttime airglow imager results at Arecibo indicate a southwestern direction of travel and 150-200 km horizontal wavelength for these waves. We have attempted to link these MSTIDs to acoustic gravity wave (AGW) forcing but have been unable to identify the necessary AGWs in the lower thermosphere or in ground-level microbarograph results. Although these waves may be linked to high-latitude MSTIDs observed with the superDARN radar network and associated with E-region auroral electrojet source(s) that are quasi-coherent under geomagnetic quiet conditions, waves generated in the auroral zone are believed to dissipate well before reaching Arecibo latitudes [Vadas, 2007]. In searching for other sources, we have identified similar (Pc6) wave periods in the GOES 10/12 magnetometer results as well as in high latitude ground-based magnetometer arrays leading us to suggest a magnetospheric source as we will discuss. Other source mechanisms such as the production of upward traveling AGWs by long wavelength ocean waves are also currently under study.



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Livneh, D. J., I. Seker, F. T. Djuth, and J. D. Mathews (2007), Continuous quasi-periodic waves over Arecibo, J. Geophys. Res., 112, DOI: 10.1029/2006JA012225. Vadas, S. L. (2007), Horizontal and Vertical Propagation, and Dissipation of Gravity Waves in the Thermosphere from Lower Atmospheric and Thermospheric Sources J. Geophys. Res., 112, DOI: 10.1029/2006JA011845.

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Analysis of meter-scale E-region plasma density irregularities from North Carolina and Puerto Rico

J. Urbina1, E. Kudeki2, S. Franke2, and R. Pfaff3

1: The Pennsylvania State University, University Park, PA, USA ([email protected]) 2: University of Illinois, Urbana, IL, USA 3: NASA/Goddard Space Flight Center, Greenbelt, MD, USA

We use radar observations from a 50 MHz radar interferometer installed near Fort Macon, Atlantic Beach, North Carolina (76°W, 34°N), to study both Low Quasi-Periodic Echoes (LQP) and Quasi-Periodic (QP) echoes in the E-region ionosphere. These meter-scale E-region plasma density irregularities observations were conducted in support of two NASA rocket campaigns in June-July period of 1999 and 2001. The radar was pointed perpendicular to the magnetic field at E-region heights over Wallops Island. E-region echoing layers were detected between 65 and 150 km altitude centered around 100 km. The median vertical distance between sampled layers is about 3 km. The median layer duration is 9 min. Over 90% of the sampled layers show a mean altitude descent rate of 22 m/s while the average ascent rate for the remaining layers is 11 m/s. In contrast to results from Puerto Rico, no events with sustained vertical stationary layers were observed (tidal ion layers) (Urbina et al. Geophys. Res. Lett 27, 2853-2856, 2000). We analyze the general characteristics of the E-region radar echoes detected during these periods and compare them with E-region events obtained in Puerto Rico with a radar of similar sensitivity. We also discuss why the characteristics of QP echoes from Puerto Rico are very different from QP echoes observed at other geographic mid-latitude radar stations by inspecting those parameters that might influence these QP layers. Finally, we will discuss the characteristics of these mid-latitude meter scale plasma irregularities with VHF radar observations of low latitude E-region in an effort to provide a global scale of these scattering layers.

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Daytime observations of mid-latitude Sporadic-E and QP radar echoes

R. Pfaff1, C. Liebrecht1, J. Urbina2, and E. Kudeki3

1: NASA/Goddard Space Flight Center, Greenbelt, MD, USA([email protected]) 2: Penn State University, State College, PA 3: Univ. of Illinois, Urbana-Champaign, IL

Although sporadic-E layers and quasi-periodic (QP) radars are typically detected during nighttime conditions at mid-latitudes, they also may exist in the daytime lower ionosphere as well. We present observations of ionosonde observations of daytime sporadic-E layers gathered at the Wallops Flight Facility, Virginia, in the late morning to noon local times. The data reveal sporadic-E characteristics similar to nighttime observations including considerable variations in frequency and altitude. For one event, observed on 23 July 1999 near 14 U.T. (10 L.T.), we present coincident strong Wallops ionosonde



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sporadic-E observations and 50MHz backscatter radar observations of quasi-periodic echoes gathered with the University of Illinois radar situated at Ft. Macon, N.C., whose beam was perpendicular to the magnetic field in the lower E-region over Wallops. The radar data show daytime QP structuring that is very similar to the nighttime observations, suggesting a similar driving mechanism. A statistical survey of the daytime ionogram data at Wallops shows a preponderance of daytime sporadic-E events occurring during the local summer months, a seasonal dependence that is well-established for nighttime sporadic-E conditions in the northern hemisphere. No clear correlation is observed between the daytime sporadic-E events and magnetic storms, suggesting that the daytime sporadic-E events are not necessarily driven by the disturbance dynamo. Rather, we speculate that the same large wind shears that are believed to be the main engine for the nighttime sporadic-E and QP echoes, may also be at work during the daytime. The existence of enhanced plasma density layers during the daytime and their role in generating QP-echoes during the day remain open questions.

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Large amplitude waves at mid and low-latitude mesosphere; a summary of observations

G. Swenson1 and A. Liu1

1: University of Illinois at Urbana-Champaign, Illinois ([email protected])

Large amplitude waves have been noted in mesospheric airglow imagery as ‘wall’ waves. A number of these events have also been observed with Na wind/temperature lidar and meteor radar at the Starfire Optical Range, Albuquerque, NM (35o N), and Maui, HI (20o N). There are a number of events that have been well characterized including Oct 9 and Oct 10, 1993, and Aug 11, 2004 at Maui, HI, and Nov 14, 1999, at Albuquerque, NM. These waves have been referred to as large atmospheric gravity waves (AGWs) or by some as atmospheric ‘bores’. These are a type of event that generates dynamic instabilities which can subsequently lead to seeding and forcing plasma instabilities in the lower thermosphere. The 4 wave events described have a great deal of similarity in their intrinsic parameters, including phase speed, direction, and phase progression with altitude. The wave attributes observed will be summarized including insights into stability conditions.

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Unusual 630.0 nm airglow variations at midlatitudes

C. Martinis1, M. Mendillo1, and J. Baumgardner1

1: Boston University, Boston, MA 02215, USA ([email protected])

Observations from the Boston University all-sky imaging system at Arecibo, Puerto Rico (18.3o N, 66.7o

W, 28o N mag lat) show an unusual behavior of 630.0 nm airglow depletions during low geomagnetic activity periods. The depleted structures moving eastward, embedded in a very bright airglow background, reverse their motion and become brighter than the surrounding ionosphere. Data from the Arecibo radar, Ramey digisonde, ROCSAT and Global positioning System (GPS) receivers are used to support the optical information. A preliminary analysis indicates that a reversal of the background electric fields and coupling with E region processes could be playing a significant role as the cause of these uncommon observations.



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Transient luminous events as lightning effects in the lower ionosphere: recent progresses by ISUAL measurements on FORMOSAT-2 satellite

T. Adachi1, Y. Takahashi2, R. R. Hsu3, H. T. Su3, A. B. Chen3, S. B. Mende4, and H. U. Frey4

1: RISH, Kyoto University, Japan ([email protected]) 2: Department of Geophysics, Tohoku University, Japan 3: Physics Department, National Cheng Kung University, Taiwan 4: Space Sciences Laboratory, University of California at Berkeley, USA

In this talk, studies on the electrical effects of transient luminous events in the lower ionosphere are summarized. The main focuses are on the spectroscopic studies of sprites and elves measured with ISUAL payload on FORMOSAT-2 satellite.

Recent discoveries of transient luminous events (TLEs: sprites, elves, blue jets and gigantic jets) visualized new aspects of the electromagnetic coupling between the troposphere and the lower ionosphere. Past experimental and theoretical studies clarified the generation mechanisms and electrodynamical processes of TLEs and their effects in the lower ionosphere. The associated subionospheric modifications were identified primarily by VLF remote sensing [Inan et al., 1995; Dowden et al., 1996; Haldoupis et al., 2004]. Numerical studies explained some parts of the experimental results [Moore et al., 2003] and expected long-time electron density modifications in the lower ionosphere by successive lightning discharges [Rodger et al., 2001].

Since 2004, the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the Taiwanese FORMOSAT-2 satellite has been measuring TLEs from space. It consists of an imager with a selectable six-color filter wheel, a six-color spectrophotometer and a dual-color array photometer. The main scientific purpose of the ISUAL is to clarify the global distributions of TLEs and to investigate their spatiotemporal and spectral properties. Chen et al. [2004] reported that sprites and elves occur all over the world, which suggests lightning effects in the lower ionosphere would be global phenomena. In order to clarify electron density modification in each sprite and elve event, several studies analyzed the ISUAL spectral data [Kuo et al. 2005; Mende et al., 2006; Adachi et al., 2006]. Adachi et al. [2006] analyzed array photometer data and estimated spatiotemporal-resolved electric field intensity in sprites. The obtained results showed a distinct transition at an altitude of ~75 km, which corresponds to the morphological transition between the upper-diffuse region and the lower-streamer region of sprites. The magnitudes of electric fields in the diffuse region were 0.6–0.8 Ek where Ek is the conventional breakdown field, supporting theoretical expectation that diffuse emissions could be produced without significant ionization process. On the other hand, those in the streamer region were 1–2 Ek, which represents significant enhancement of the electron density. Mende et al. [2005] also presented evidence of electron density enhancements in elves based on spectrophotometer measurements. The electron density enhancement in an elve event was estimated to be 210 electrons cm-3 over a region of 165 km at an altitude of 90 km, comparable to the ambient electron density in the nighttime D-region ionosphere. More recently, Mika et al. [2006] carried out comprehensive observations using VLF receivers, ground-based camera, and ISUAL imager. The obtained data showed direct relation between subionospheric VLF perturbations and elve events.

By summarizing the recent progresses, current problems and future studies about lightning effects in the lower ionosphere are further discussed.



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Particle simulations of optical emissions in sprite streamers

O. Chanrion1, T. Neubert1, and H. Stenbaek-Nielsen2

1: National Space Institute, Technical University of Denmark ([email protected]) 2: University of Alaska, Fairbanks

The optical emission rates of sprites in the mesosphere contain important information on the discharge process. A precise understanding of the process is needed in order to estimate perturbations of sprites to the composition, density and temperature of the mesosphere. For this purpose, a particle code has been developed to study electric discharges in the atmosphere. The code simulates the development of discharges from seed ionization through electron avalanches into streamers. The code is based on the particle-in-cell (PIC) technique for updating the electron velocities and their positions and for calculating the self-consistent spacecharge fields. A Monte Carlo technique (MC) is used for simulating interactions with the ambient atmosphere including excitation and emission rates. The code is in 2D cylindrical coordinates, giving realistic spatial variations of the fields during the initial stages of a discharge presented here. The simulations of optical emission rates are compared to recent high-speed imaging observations of sprites, which allow for a simple and robust estimation of the instantaneous emission rate in streamer heads. The presentation will discuss electric fields, electron energetics and optical emission rates in the streamer head region.

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Investigations of effects of infrasound on the ionosphere

J. Lastovicka, D. Buresova, J. Chum, and T. Sindelarova

Institute of Atmospheric Physics, ASCR, Prague, Czech Republic ([email protected])

Among atmospheric waves influencing the ionosphere, the infrasonic waves are the least known and least studied waves, even though they could also contribute to coupling of the lower-lying atmosphere and ionosphere. Model computations show that only long-period part of their spectrum can reach ionospheric heights. Special problems with signal distortion and heavy energy dissipation in the so called transition region were found for signals generated by point sources. Analysis of several strong meteorological events revealed well-pronounced infrasound oscillations in the ionosphere for minority of events over the Czech Republic. Peculiar phenomena in the infrasound time-scale region, so called S-shapes and quasi-linear shapes (QLSs) observed in Doppler spectrograms, have been studied, their statistical characteristics determined and possible mechanisms investigated. In 2007 we introduced three new Doppler measuring paths, so now we have five measuring paths with central receiver in Prague; three ground-based microbarographs have been installed in December 2007 - January 2008. Thus now we have observational system which should make possible more detailed studies and better localization and determination of infrasound events in the ionosphere and their possible relation to tropospheric/surface-located events.


Poster P3: Posters for Session S7 (Ionospheric electrodynamics: Theory and numerical modeling)

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The behavior of the TEC and equatorial electrojet during April 8, 2005 solar eclipse



In the given work the results of numerical calculations of global distribution of TEC and linear density of zonal current in the ionosphere of the Earth during a solar eclipse are presented. Calculations have been executed on the basis of Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), developed in WD IZMIRAN, added by the new block of calculation of electric fields in the ionosphere of the Earth. In calculations we considered superposition of magnetospheric convection electric field and dynamo field generated by thermospheric winds without taking into account the thermospheric tides. The solar eclipse of hybrid type viewed in the given work has occurred on April, 8, 2005. The hybrid eclipse was visible from within a thin corridor, which traverses the Southern Hemisphere. The path of the shadow of the Moon has begun southeast of New Zealand and stretched across the Pacific Ocean to Panama, Columbia, and Venezuela. The eclipse has begun at 18.54 UT and has ended at 22.15 UT. From 20.30 UT till 21.10 UT the shadow of an eclipse transited in a neighborhood of geomagnetic equator. It is shown, that the solar eclipse caused impairment of equatorial electrojet intensity twice. First time it has occurred at the initial stage of the eclipse due to change in ionosphere conductivity in the region of influence of field aligned currents. It has led to change of distribution of magnetospheric convection electric field (18.58 UT - 19.06 UT). Second time it has occurred during the passage of a solar eclipse through geomagnetic equator with delay of 30 min (21.00 UT - 21.20 UT) due to local changes of ionospheric conductivity in the region of the eclipse and reorganization of thermospheric circulation to which the time delay is related. It has led to change of distribution of dynamo field in the region of geomagnetic equator. The measurements on CHAMP satellite by Tomas et al., 2007 the variations of EEJ during this solar eclipse have revealed 40% reduction in comparison with quiet conditions. For the same time moments the results of our calculations give 46% reduction EEJ. The reduction of TEC during an eclipse is equal less than 5%. Delay of effects of solar eclipse in TEC is observed at mid-latitudes. It disappears at geomagnetic equator.

References

Tomas A.T., Lühr H., Foerster M., Rentz S., and Rother M. Observations of the Low-Latitude Solar Eclipse on 8 April 2005 by CHAMP. J. Geophys. Res., Vol.112, A06303, 2007.

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Effects of substorms with different moments of the beginning in equatorial electrojet and parameters of F-region of Equatorial Ionosphere





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In the given work the calculation results of four modeling substorms beginning in 00 UT, 06 UT, 12 UT and 18 UT for spring equinox conditions in a minimum of solar activity (F10.7 = 76) are submitted. Calculations were carried out on Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), developed in WD IZMIRAN, with use of the new calculation block of electric fields of a dynamo and magnetospheric origins. For all four substorms the time course of the intensity of westward and eastward equatorial electrojet was obtained. Calculations have shown, that during the substorms beginning in 06 UT and 18 UT, there is a reduction of intensity of the counter electrojet from - 12 A/km in quiet conditions down to - 4 A/km; during the substorms beginning in 00 UT, there is the counter electrojet easing from - 8 A/km in quiet conditions down to - 4 A/km, and during the substorms beginning in 12 UT, the counter electrojet practically does not vary. At the same time the eastward equatorial electrojet intensity during the substorms beginning in 00 UT and 12 UT decreases from ~50 A/km in quiet conditions down to ~40 A/km; during a substorm beginning in 06 UT, its intensity decreases down to ~15 A/km, and for a substorm beginning in 18 UT, it in the beginning grows up to 65 A/km, and then falls down to 40 A/km. Global distributions of foF2 perturbations calculated for the substorm which has begun in 18 UT are submitted, and their temporal course during a substorm and after its termination is analyzed. Calculations have shown that at geomagnetic equator the precise semidiurnal harmonic in foF2 perturbations with maxima of positive disturbances in post-sunset and pre-sunrise hours and maxima of negative disturbances in post-midnight and near-midday hours is traced. Negative ionospheric disturbances are observed mainly at night from subauroral latitudes up to geomagnetic equator. By the moment of the substorm termination the positive disturbances in the post-sunset sector at geomagnetic equator considerably amplify. Calculation results of the foF2 temporal course during substorms are submitted and analyzed for equatorial, low- and mid-latitude stations.

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Forming of the ionospheric precursors of the earthquakes by zonal electric field

A. A. Namgaladze1, M. V. Klimenko2, V. V. Klimenko3, and I. E. Zakharenkova3

1: Murmansk State Technical University, Murmansk, Russia 2: Kaliningrad State Technical University, Kaliningrad, Russia ([email protected]) 3: West Department of N.V. Pushkov Institute of Terrestrial Magnetizm, Ionosphere and Radio Wave Propagation (IZMIRAN) of Russian Academy of Science, Kaliningrad, Russia

A physical mechanism has been proposed for the forming of areas of increased or decreased total electron content (TEC) in the ionosphere as observed by the measurements of the GPS signal delays before strong earthquakes. The main cause of these TEC disturbances is the vertical plasma transport under action of the zonal electric field directed eastward (westward) in cases of the positive (negative) TEC disturbances at midlatitudes and in cases of strengthening (disappearance) of the F2-region equatorial anomaly. The spatial potential pattern for such electric field has been proposed. For the eastward (westward) electric field existence at the near-epicentral region it is necessary, that the positive (negative) electric charges have been located at the western boundary of this region, and the negative (positive) charges at the eastern boundary. To investigate an efficiency of the proposed mechanism the numerical model calculations have been performed. The ionosphere reaction to the action of the electric field created by such configuration of charges has been calculated. The numerical calculation results revealed an excellent agreement with the TEC observations before the strong earthquakes at mid- and low latitudes.



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Comparative study of some parameters of equatorial electrojet in West African and Indian sectors

Rabiu, A. B.

Space Physics Laboratory, Department of Physics, Federal University of Technology, AKURE, Nigeria. ([email protected])

Some parameters of the equatorial electrojet EEJ over West African and Indian sectors dip equator. The electrojet centre has a consistent diurnal variation pattern and comes closer to the dip equator at about local noon when the intensity of the jet maximizes. The current have been evaluated from Onwumechili’s thick current shell format of continuous current distribution model of equatorial electrojet and compared. Ground data taken during the International Equatorial Electrojet Year IEEY and routine observations were used for the West African and Indian sectors respectively. The parameters studied are centre, width and thickness of the EEJ. The thick current shell model, which takes into account the vertical ionospheric currents, permits both the width and the thickness of the jet to be determined simultaneously. The diurnal variations of each of the parameters are consistently similar in different sectors. The electrojet axis at both sectors does not coincide with the width (thickness) increase (decrease) from dawn towards the local noon and thereafter begin to decrease (increase) towards sunset. Seasonal and annual mean values of the parameters are obtained and discussed. The interplay between the variation of current width and thickness is explained in terms of the wind shears in consistency with the electrodynamics of the dynamo region. The variation of the EEJ centre is explicable by the dynamics of meridional winds.


Poster P3: Posters for Session S8 (Coupling processes at low- and mid-latitudes)

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The effect of non-migrating tides on the equatorial electrojet

Hermann Lühr1, Martin Rother1, Kathrin Häusler1, Patrick Alken2, and Stefan Maus2

1: GeoForschungsZentrum Potsdam, Potsdam (hLü[email protected]) 2: Cooperative Inst. for Research in Environm. Sci., University of Colorado, Boulder, CO

Abstract. The climatological model of the equatorial electrojet, EEJM-1, derived from Ørsted, CHAMP and SAC-C satellite measurements [Alken and Maus, 2007] provides the opportunity to investigate the longitudinal variation of the current strength in detail. Special emphasis is put in this paper on the effect of non-migrating tides. We have found that the influence of the diurnal eastward propagating mode with wavenumber 3, DE3, is particularly strong. In polar orbiting satellite observations the DE3 tidal signal appears as a four-peaked longitudinal structure. The amplitude of the DE3 signature in the EEJ peaks during equinox seasons, but it is also strong around the June solstice. When looking at the relative modulation depth of the EEJ intensity the DE3 accounts for about 25% during the months April through September. It is thus the dominant cause for longitudinal variations. During December solstice months the influence of DE3 is negligible. A secondary three-peaked longitudinal pattern emerges during solstice seasons when the DE3 influence is removed. From the data available it is, however, not clear whether this pattern is related to any tidal drivers.

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Study on the Perkins instability by E-F coupled three-dimensional simulation model

T. Yokoyama1, Y. Otsuka2, M. Yamamoto3, and D. L. Hysell1

1: Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, USA ([email protected]) 2: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan 3: Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan

Since the discovery of turbulent upwellings associated with midlatitude spread F with the MU radar, the midlatitude ionosphere has been intensively studied. Two-dimensional airglow images and GPS-TEC maps have revealed that banded structures, or medium-scale traveling ionospheric disturbances (TIDs), frequently occur in the nighttime midlatitude ionosphere under low solar activity condition. They are aligned from northwest to southeast (NW-SE) in the northern hemisphere with a wavelength of a few hundred kilometers and travel southwestward with a velocity of approximately 100 m/s. Although the Perkins instability may be the most likely mechanism to explain the TID structures, the rapid growth and the southwestward propagation of the TIDs cannot be derived from the linear theory of the Perkins instability. We have developed a three-dimensional numerical simulation including the nighttime midlatitude E and F region ionosphere for the first time and applied to the Perkins instability in the midlatitude F region. Growth of the Perkins instability is successfully reproduced under low solar activity nighttime condition, and the numerical results basically agree with linear theory and previous two-dimensional numerical studies when only the F region is considered. The new finding of this study is that the coupled E region has a significant effect on the Perkins instability even though the density in the E region is two orders less than in the F region. The neutral wind plays an important role in modulating the density profile and current in the E region. More studies of the coupled ionosphere can be done in the near future.



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E and F region coupling between an intense sporadic E layer, an MSTID, and a neutral atom layer

W. E. Swartz1, M. C. Kelley1, and N. Aponte2

1: Cornell University, Ithaca, New York, USA ([email protected]) 2: Arecibo Observatory, Arecibo, Puerto Rico

Considerable controversy exists concerning the relative roles of the E and F regions in controlling irregularity formation in the mid-latitude ionosphere, largely because electric fields due to a plasma instability in one region may map to the other if the perpendicular scales are sufficiently large. In this paper we look at a particularly fortuitous data set in which both E and F-region observations were made using incoherent scatter radar (ISR), GPS, lidar, and coherent scatter radar (CSR). In this event, a dense, patchy sporadic E layer was detected that exhibited type I (two-stream) coherent echoes while, at the same time, the F-layer plasma was highly structured with plasma drifts of hundreds of m/s. We examine this event in the context of a mesoscale travelling ionospheric disturbance (MSTID). The data presentation will be followed by comparison with current theories for coupling between these two regions.

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Perspectives of electrostatic coupling on various manifestations of low-latitude E and F region irregularities related to equatorial plasma bubble studied in

the Indian sector

A. K. Patra1, N. V. Rao1, N. Dashora1, T. K. Pant2, and K. Niranjan3

1: National Atmospheric Research Laboratory, Gadanki, India ([email protected]) 2: Space Physics Laboratory, VSSC, Trivandrum, India 3: Department of Physics, Andhra University, Visakhapatnam, India

Electrostatic coupling between the E and F regions of the ionosphere has become a subject of intense scientific investigation due to its relevance in exciting/suppressing plasma irregularities in a non-local sense. Recent radar observations made from low latitudes showed that the E region irregularities are disrupted during the development phase of equatorial plasma bubble. It was hypothesized that this E region manifestation is due to the effect of non-local electric field that is of equatorial plasma bubble origin. On the other hand there also exists experimental evidence of disruption of low latitude Es concurrent with large values of pre-reversal electric field. Studies suggested that this disruption is due to the shear in the vertical electric field associated with the evening equatorial F region. Notably, this electric field structure is responsible for the evening F region vortex, an important precursor of equatorial F region irregularities. A clear understanding on the two observational facts, however, has not yet emerged.

On the other hand, growth of the pre-reversal enhancement in electric field and also the growth of plasma bubble have been shown to be dependent on the low latitude E region conductivity. Considering that low latitude E region conductivity is important for the growth of the topside F region irregularities, it is expected that E region conductivity would also control the fate of the already existing F region irregularities. In the later part of the evening, when further growth of bubble does not take place, the life of the existing irregularities then would be influenced by the low latitude E region conductivity, thus deciding the fate of the irregularities in the late night hours. This becomes important since the low latitude conductivity could vary significantly due to the height-time variation of Es layer, presumably controlled by tidal and gravity wave winds.



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This paper is meant to address three important manifestations in the low latitude E and F regions in connection with the equatorial plasma bubble based on observations made using the Gadanki radar and a network of ionosonde in the Indian sector. First, the paper will deal with what happens to the E region both in terms of electron density and electron density irregularities during the development phase of equatorial plasma bubble. Importantly, it will address the two observational facts related to disruption of Es and irregularities reported earlier, but not resolved. Second, the paper will deal with the fate of the already exiting F region irregularities due to the evolving electron density structures in the low latitude E region. Third, how far the valley region irregularities are dependent on the E and F region processes.

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Simulations of strong wind shears in the mesosphere and their effects on structure of the E-layer

P. A. Bernhardt1, J. Werne2, and M.F. Larsen3 1Plasma Physics Division, Naval Research Laboratory, Washington, DC 2Colorado Research Associates, Northwest Research Associates, Inc., Boulder, CO 3Department of Physics and Astronomy, Clemson University, Clemson, SC

Wind shears are a strong candidate for the production of sporadic-E layer irregularities. Three-dimensional simulations of shear driven neutral atmospheric turbulence have been applied to the mesosphere and lower thermosphere. The two processes that generate regions of neutral turbulence in stable stratification are wind-shear instability and gravity-wave breaking. Using chemical release trails and ground based LIDAR measurements, the change in the neutral wind shear between 100 and 120 km altitude is typically 300 m/s over distances as short as 10 km. With measured wind active shears, the computed Richardson Numbers are commonly much less that 0.25 so that Kelvin-Helmholtz instabilities are excited to yield locally neutral turbulence. This turbulence couples into the E-region plasma that is simultaneously maintained by the wind shears. The resulting ionospheric irregularities can scatter radio waves and affect propagation through the sporadic-E layer. Both two- and three-dimensional computational models have been used to determine the effects of strong, unstable wind shears on the E-region.

Wind shears drive turbulence that is temporally episodic (nonstationary), spatially intermittent (inhomogeneous and anisotropic) and nearly always smaller than the grids used in atmospheric models. The kinematic viscosity determines the scale size of the turbulent structures as quantified by the Reynolds number in the region. Near 120 km altitude, the Reynolds number is about 300 and the computational resolution required for accurate modeling is about 20 meters. At 100 km altitude where the Reynolds number is closer to 3000, the computation grid for turbulence modeling needs to be spaced by at most 4 meters. The nature of the Kelvin-Helmholtz turbulence is affected by the amount of turning in the wind shear. Planer shears with no turning component commonly found in the troposphere produce Kelvin-Helmholtz (K-H) billows that have longitudinal filaments in the direction of the shear. The mesosphere, however, always has wind shears with strong turning components. The first 3-D simulations of neutral K-H driven instabilities with strong turning shears will be presented here. In these simulations, the K-H billows contain internal structures that rotate opposite to the primary billow and the longitudinal structures are organized obliquely to the largest shear component.

The neutral velocities provided by the three-dimensional neutral simulations are applied to a two-dimensional electrostatic model of the E-layer. The ions and electrons respond to the neutral turbulence forcing by producing distorted billows and plasma layering. The detailed structures are dependent on the ratio of the ion-neutral collision frequency to the ion cyclotron frequency. At 120 km altitude where these



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frequencies are nearly equal, the plasma structures clump in response to the neutral K-H turbulence. At 100 km altitude where the ions are unmagnetized because of large ion-neutral collision frequencies, the plasma forms elongated filaments in response to the neutral turbulence. In addition, large electric fields greater than 50 mV/m are initiated as the K-H instability forms coherent structures. When fully developed neutral turbulence sets in, the electric field amplitude drops and the scale size of the structures becomes smaller. Computed irregularity spectra are produced for comparison with in situ and radar scatter observations.

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E- and F-region coupling revealed by nighttime MSTID and sporadic E layer observations with the mid-latitude SuperDARN Hokkaido radar!

T. Ogawa1, N. Nishitani1, Y. Otsuka1, K. Shiokawa1, T. Tsugawa2, and A. Saito3!

1: Solar-Terrestrial Environment Laboratory, Nagoya University, Japan ([email protected]) 2: National Institute of Information and Communications Technology, Japan 3: Department of Geophysics, Graduate School of Science, Kyoto University, Japan!

The SuperDARN Hokkaido HF radar at Rikubetsu in Hokkaido, Japan (43.5oN, 143.6oE; 36.5oN geomagnetic) started operation in December 2006. This radar, equipped with 16 narrow oblique beams, can cover a wide area to the northeast of Hokkaido, and is very suitable for the studies of high- and mid-latitude ionosphere. In this paper, we present coherent radar echoes associated with nighttime medium-scale traveling ionospheric disturbances (MSTIDs) and sporadic E (Es) layers over the Sea of Okhotsk. Echo data are analyzed together with data from a dense GPS network (GEONET), which provides detailed total electron content )TEC* maps over Japan, and from a 630-nm all-sky imager at Rikubetsu. Main results are as follows: 1) Echoes associated with nighttime MSTIDs are due to F-region field-aligned irregularities (FAIs). 2) These echoes are mostly accompanied by Es-FAI echoes. 3) Spatial structures of nighttime MSTIDs observed by GEONET and the imager are well coincident with Es-FAI echo regions, and MSTID-FAI echo regions are connected with Es-FAI echo regions through the geomagnetic field, both suggesting an electrical coupling between the E- and F-region. The existence of such a coupling have been recently found over the central Japan using the MU radar, GEONET and all-sky imager at Shigaraki (34.9N; 136.1oE; 25.0oN geomagnetic). 4) Peculiar quasi-periodic echoes (QPE) from nighttime Es layers were first observed by the MU radar. We show examples of MSTID-associated QPE for the first time detected by the Hokkaido radar.

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On the instability of sporadic E layer formation under vortical neutral wind motion at mid-latitude

S. Shalimov1,2, T. Ogawa3, and Y. Otsuka3

1: Institute of Physics of the Earth, Moscow, Russia ([email protected]) 2: Space Research Institute, Moscow, Russia 3: Solar-Terrestrial Environment Laboratory, Nagoya University, Japan

Since the development of wind shear theory at mid-latitude [Whitehead, 1961; Axford, 1963] it is well known that metallic ions immersed in a zonal wind shear will converge toward a shear node, where zonal wind is zero, thus producing sporadic E layers. However, it turns out to be that under this condition



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horizontal Es layer cannot exist in a homogeneous steady-state relative to small perturbations [Gershman et al., 1968].

The idea by Gershman et al. [1968] has been developed to include also a propagating internal gravity wave as a perturbation. The instability process during initial stage of a sporadic E layer formation when the thin layer by itself does not exist is considered. The growth rate of the instability has been found and it has been shown that it depends on perturbation wavelength. The conditions for the instability are favorable when the vorticity of the neutral motion becomes antiparallel to the geomagnetic field. The vorticity may be attributed either with a large scale wind shear or with propagation of a short-period internal gravity wave. Thus we may conclude that the vorticity plays the main role in the instability of sporadic E layer formation, while the diffusion term plays stabilizing role.

Finally, a comparison of our results with recent theoretical and experimental approaches concerning the understanding of unstable sporadic E layer conditions shows the possibility of E/F layer coupling when perturbation for the sporadic E layer can be produced by the propagating MSTID in the F region.

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Observations of acoustic-gravity waves in the ionosphere generated by severe tropospheric weather

T. Sindelarova, D. Buresova, and J. Chum

Institute of Atmospheric Physics, CAS, Prague, Czech Republic ([email protected])

Weather systems in the troposphere are well known as a source of acoustic and gravity waves. Ionospheric effects of meteorological origin partially depend on geographical location and on its orography. Using high frequency continuous Doppler sounding system located in the Czech Republic, we monitor the wave activity in the bottomside ionosphere during increased meteorological activity. During three years of sounding we registered gravity waves with periods of 10-20 minutes during several convective storms, while the acoustic waves of tropospheric origin were observed only under exceptionally severe weather conditions. As at the single geographical locations weather systems develop and act under different conditions, e.g. different characteristics of convective storms in the central part of the North America and in the Europe, the observed ionospheric effects are also different. Recently we examine what kind of tropospheric weather phenomena is most efficient in generating acoustic and gravity waves effecting ionosphere above Central Europe.

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Variability and descent of mid-latitude sporadic E layers at Arecibo

N. Christakis1, C. Haldoupis2, Q. Zhou3, and C. Meek4

1: Department of Applied Mathematics, University of Crete, Heraklion, Greece ([email protected]) 2: Physics Department, University of Crete, Heraklion, Greece 3: Department of Electrical and Computer Engineering, Miami University, Oxford, Ohio, USA 4: Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada

Contrary to what the name implies, mid-latitude “sporadic E layers” (Es) follow regular patterns in variability and altitude descent which are primarily determined by the confluence of the vertical tidal wind shears in the lower thermosphere. Although there is a good deal of knowledge on these variations, mostly because of case studies with the incoherent scatter radar (ISR) at Arecibo, there are still unresolved



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questions which require further study and more observations. In the present work we use a novel method to analyze an extended data set of sporadic E layer ISR radar measurements, made at Arecibo over many years with continuous radar runs lasting from a few to several days, and with a reasonably good seasonal coverage. Here, instead of using the measured electron density as a function of altitude and time to trace the layers, we use the vertical electron density gradient. This turns out to be a fairly sensitive parameter in tracing the altitudinal layer structure and in identifying equally well both strong and weak layers. Our analysis confirms that the diurnal tide is the key agent responsible for forming and dragging the layers downwards below about 120 km and thus determining the regular occurrence of sporadic E layers. On the other hand the role of semidiurnal tides on Es variability and descent is found to be on the average less decisive. Also there is limited evidence of gravity wave effects on the diurnal variations and descent of Es. Furthermore, the general Es pattern in variability and descent does not appear to bear a systematic seasonal difference, which implies that the tidal variability does not contribute seriously to the pronounced seasonal dependence of mid-latitude sporadic E layers. Finally, a simple and well known model, based on the steady state solution of the momentum equation for the vertical ion drift, is used to fit dominant descending patterns in the observed Es traces. In this way, we obtain estimates for the amplitudes, phases as well the vertical wavelengths, and thus the vertical phase velocities, of the diurnal tide in the lower thermosphere between about 120 and 90 km.

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Ionosphere-thermosphere coupling in low latitude region

S. Watanabe1, H. Liu1 and M-Y. Yamamoto2

1: Hokkaido University, Sapporo, Japan 2: Kochi University of Engineering, Kochi, Japan

Though the ionization rate is less than 1% in the region of thermosphere, the dynamics of neutral atmosphere is strongly controlled by the plasma. The coupling process between the neutral atmosphere and the plasma has been investigated by satellites such as DE-1, AE and CHAMP. The CHAMP satellite indicated that the solar flux influences significantly the equatorial zonal wind with the maximum velocity on the magnetic equator. The winds show super rotation of thermosphere depending on the season and solar flux. Large-scale stationary electron density inhomogeneities in longitude were obtained by CHAMP and Hinotori satellites in the F-region. The 10000-km scale longitudinal variation in ionosphere may result in a strong connection between troposphere and ionosphere by diurnal atmospheric tides driven by weather in the tropics.

JAXA/ISAS launched successfully S-520-23 sounding rocket from Kagoshima Space Center (KSC) in the evening of September 2, 2007. The rocket experiment is called WIND (Wind measurement for Ionized and Neutral atmospheric Dynamics study). The purpose is to investigate the neutral atmosphere - plasma coupling process in F-region through the measurements of atmospheric circulation and super rotation in the low latitude thermosphere, and a medium scale traveling ionospheric disturbance (MS-TID) occurring in the mid-latitude ionosphere. The rocket installed Lithium release canisters as well as instruments for plasma drift velocity, plasma density and temperature and its fluctuations, and electric and magnetic fields. The Lithium gas was released at altitudes between 150km and 300km, and the lithium scattered sunlight by resonance scattering with wavelength of 670 nm. The neutral winds in the thermosphere were estimated from the movements of Lithium clouds observed by CCD imagers on ground. From the diffusion of lithium clouds, we estimated neutral density and temperature in the thermosphere.



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In this paper, we discuss the ionosphere-thermosphere coupling process from the results of CHAMP and Hinotori satellites and rocket experiment (WIND).

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Inter-annual and long-term variations observed in the ITM system

E. R. Talaat 1, J.-H. Yee1, L. J. Paxton1, James Russell III2, Martin G Mlynczak3, R. DeMajistre1, and A. Christensen4

1, The Johns Hopkins University Applied Physics Laboratory ([email protected]) 2. Hampton University 3. NASA Langley Research Center 4. Aerospace Corporation

The Ionosphere-Thermosphere-Mesosphere (ITM) region is highly variable and has a complex system of drivers including variable solar radiation, geomagnetic activity, and forcing from the lower atmosphere. Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become the most prominent dynamical features of the ITM. Planetary and gravity waves modify the zonal mean temperature and winds through dissipation and momentum deposition. The effects of these waves on the ITM are expected to depend on the level of solar activity. For all types of waves, how high they penetrate into the thermosphere depends on the temperature, wind, and viscosity profiles. Current observations have shown signatures of both gravity waves and planetary waves in upper atmospheric measurements of winds, temperature, and ion density.

The momentum deposition from upward propagating waves is thought to generate the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. Recent global observations of the low latitude neutral atmospheric and ionospheric structure revealed by TIMED/SABER, TIMED/GUVI, TOPEX, and JASON allow us to investigate the interplay between the neutral, plasma, and background fields. Specifically, we will discuss inter-annual variability observed in mesosphere and lower thermosphere zonal mean temperatures and waves and examine the solar activity effects on the low-latitude ionosphere on different timescales – including solar flare, rotational, and 11-year solar cycle effects and possible indicators of coupling between the lower and upper atmosphere.

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On the linking of large-scale wave like modulations in the TEC to the EEJ strength over India: Is it due to planetary scale waves?

S. Sripathi, S. Bose, D. Tiwari and, A. Bhattacharyya


In this paper, we present the analysis of magnetic and GPS data that suggests that there is a strong association between the equatorial electrojet (EEJ) strength and the modulations in the total electron content (TEC) as obtained from GPS observations during January to March 2006. It is well known that zonal electric field over the EEJ region drives the daytime ionization to higher altitudes through EXB drift



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and this ionization slowly descends to higher latitudes through diffusion along the magnetic field lines. The zonal electric field inturn depends on the atmospheric waves mainly associated with tides. The IMAGE satellite observations suggest that atmospheric tides can influence the equatorial ionization anomaly (EIA) dynamics through modifying the zonal electric field over the dip equator that produce EIA. Recent observations also suggest that large scale waves like quasi-2-day wave, 5-day wave and 16-day wave do influence the low latitude electrodynamics. In this context, we have performed a study to understand the association between the strength of the EEJ current and the variations in the TEC over Indian region at different stations. Wavelet analysis suggests that the EEJ strength and the TEC variations have a periodicity of nearly 16-day period. The observations further suggest that these large-scale modulations are prominently seen over EIA region. It may be noted that possible sources for the changes in TEC are mainly due to (a) Solar flux, (b) Geomagnetic storms and (c) the vertical EXB drift. Since the TEC data which we have used for the present analysis belongs to magnetically quiet period and also the solar flux does not show any periodic variations, we are left with the sources which can influence the EXB drift. Since we have identified almost similar periods in both EEJ strength and TEC, it is conjectured that these large-scale wave like modulations in TEC can be associated with atmospheric planetary scale wave phenomenon that is modifying the EEJ current and EXB drift velocity. Observations of satellite data like CHAMP and DMSP are also used to see any large-scale periodic variations in the density data during the same period and will be presented in the full length paper.

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The 7-day planetary wave oscillations in the ionosphere and MLT revealed by TEC, UKMO and AURA

Jiangang Xiong, and Weixin Wan

Institute of Geology and Geophysics, Chinese Academy of Sciences ([email protected])

The 7-day planetary wave oscillations in the ionosphere revealed by TEC are strong around 150N and 15oS, which are equatorial anomaly crest regions, around spring vernal equinox from 2004 to 2005. The oscillation in 2005 spread to equator but not in 2004. The oscillation amplitude is greater than 1TECU and it propagates westward with wave number one. The 7-day or 6.5-day oscillation in MLT has been known for many years which is strong around equinox. The oscillation in MLT has wavenumber one and their propagation direction is westward from UKMO and AURA/MLS. The propagation characteristic parameters are similar in the MLT and ionosphere. But the oscillation in the ionosphere around the autumnal equinox is weak. The oscillation in the ionosphere may not caused directly by waves in the MLT. The wind dynamo by oscillation in the MLT around equator may be the main source of the oscillation in the ionosphere around equatorial anomaly crest regions.

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Variability of vertical drifts during storm -times at equatorial latitudes

E. Pacheco, and R. Heelis

University of Texas at Dallas, USA ([email protected])

We utilize measurements from the DMSP and ROCSAT satellites of the years 2000-2003 to investigate the storm time dynamics of the equatorial topside ionosphere at different local times and longitudes during the same events. Our study focuses on the longitudinal and local time variation of the ion drift perturbations and will complement radar studies that are limited to a fixed longitude and latitude. The



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DMSP F13 and F15 satellite data are gathered consistently at four different local times at the equator near 800 km altitude. The ROCSAT satellite data are then used to verify the observed behavior. ROCSAT provides data at additional local times near 600 km altitude and also at the same local times as DMSP. We have selected data from storms for which the values of the Dst index are less than -200 nT in order to determine the appearance of systematic repeatable storm time behavior observed in satellite measurements.

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Longitudinal signatures of tidal influence on topside ionosphere at low latitudes by means of DEMETER and DMSP-f15 data

L. Bankov1, M. Parrot2, R. Heelis3, J-J. Berthelier4, and A. Vassileva1

1: Space Research Institute at the Bulgarian Academy of sciences, 6 Moskovska str. Sofia 1000 Bulgaria ([email protected]) 2: Laboratoire de Physique et Chimie de l’Environnment, CNRS, 45071Orleans-CEDEX 3: “William B. Hanson” Center for Space Science, UT Dallas, Richardson TX 75080 4: CETP/IPSL, 4 avenue de Neptune, 94100 SAINT-MAURPlasma probe data from DEMETER and DMSP-f15 satellites were used to examine the longitudinal behavior of ion density and temperature distribution in the topside equatorial ionosphere. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite was launched on June 29 2004 at near circular Sun synchronous orbit (SSO) with 98° inclination at 710-730km initial height with approximate local time of the orbital ascending node ~2230LT. Onboard satellite, thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. In parallel to DEMETER, as a part of “Defense Meteorological Satellite Program”, DMSP-f15 is on orbit operation since 1999 onto circular SSO with 96° inclination at ~830-840km with ascending node local time ~2130LT.. Onboard DMSP-f15, ionospheric plasma diagnostics was made by means of “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. Here we use SSIES-2 and IAP data to present longitudinal variations in ionospheric plasma at low latitudes during one year period of low solar activity from August 2004 to August 2005. The observed seasonal and altitude behavior of longitudinal structures are discussed in the scope of recently discovered “wave-number four” undulation of low latitude F-region plasma by non migrating tides.

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Evolution of ionospheric disturbances generated by large earthquakes

Elvira Astafyeva1,2, Kosuke Heki1, Edward Afraimovich2, Vladislav Kiryushkin2, and Sergey Shalimov3

1: Department of Natural History Sciences, Hokkaido University, Sapporo, Japan ([email protected]) 2: Institute of Solar-Terrestrial Physics SB RAS, Irkutsk, Russia 3: Institute of Physics of the Earth RAS, Moscow, Russia

Earthquakes are known to generate atmospheric disturbances. Vertical displacements of the ground induce pressure waves in the neutral atmosphere (acoustic-gravity waves) that propagate upward and grow in amplitude by several orders of magnitude as they attain ionospheric heights, since the atmospheric density decreases with height. Such waves can initiate the ionosphere plasma motion due to interaction via



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collisions between neutral and charged particles, and produce perceptible perturbations in the ionosphere electron density.

Using GPS total electron content (TEC) measurements we studied ionosphere response to the Kuril Islands Earthquakes of 04 October 1994 (M8.1) and 15 November 2006 (M7.9). High spatial resolution of the Japanese dense GPS array (GEONET) allowed us to analyze the dynamical characteristics of the observed traveling ionospheric disturbances (TIDs) in detail. This provided us more information about the processes of an atmospheric wave propagation and transformation from the ground to the ionosphere (i.e. transformation of acoustic waves to shock-acoustic waves, SAW) and then to TIDs propagating for more than 1800 km. Such observations of the evolution of disturbances in the ionosphere have been performed for the first time.

According to our observations and calculations, the shape of TEC response and velocity of the TID propagation changed with distance from the TID source.

The observed TIDs appeared in TEC records of the closest GPS receivers ~10 min after the quake in the form of N-type wave as a response to propagation of SAW. The amplitude of the signal is about 0.6 TEC units for the records in the near-field (~100-200 km) of the suspected TIDs source, and about 1 TEC units at a distance of 200-350 km. Within first 600 km the propagation velocity was about 1.3 km/s. Our results coincide with previous results of SAW investigations (Afraimovich et al., Ann.Geophys., 19, N4, 395-409, 2001; Heki and Ping, EPSL, 236, 845-855, 2005).

We managed to track the subsequent evolution of the propagating TIDs: starting from ~400-500 km out of the source the wave seems to divide into two separate waves, which henceforth propagate with different velocities - about 1.7 km/s and 600 m/s. We suggest that the TEC response in the far field of the TIDs source is a mixture of the damping SAW (the “fast” wave) and TIDs propagating in the atmospheric waveguide (the “slow” wave). Other possibility is that the record shows separation of the positive (the “fast” wave) and negative (the “slow” wave) phases of the N-type wave during its evolution.

Our observations and ionosphere response parameters estimations are in agreement with results of modeling of ionospheric variations due to earthquakes (Ahmedov and Kunitsyn, Geomagnetism and Aeronomy, 44(1), 2004; Shinagawa et al., EPS, 59, 1015–1026, 2007).

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More observations for testing the relationsphip between Sprites and subionospheric Early VLF signal perturbations

N. Ambrosiadi, C. Haldoupis, and A. Mika

Physics Department, University of Crete, Heraklion, Crete, Greece ([email protected])

The last few years there is a collaborative effort in Europe to study the physical processes in relation with “Transient Luminous Events” (TLEs), mainly sprites and elves. To this objective, a number of EuroSprite campaigns were conducted throughout the last five summers using ground-based equipment for coordinated observations during sprites occurring mostly over France. The University of Crete participated in these campaigns by contributing VLF measurements made with a narrow-band receiver in Crete, that was provided by the Stanford University. The present paper comes as continuation of work based on the analysis of EuroSprite optical and VLF observations for the purpose of investigating the effects on the nighttime D region during TLE occurrences. According to previous EuroSprite studies a nearly one-to-one relation was found to exist between sprites and “early” VLF perturbations which suggested an abrupt ionization production in the upper D region occurring concurrently with the sprite emissions. This interesting result was thought, however, to be tentative because it was based on a few



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sprite-producing storms observed during the summer 2003 EuroSprite campaign. Here we test further this result by carefully analysing a much larger data set of simultaneous spite and VLF observations obtained from several EuroSprite campaigns. Our results suggest that the relationship between sprites and early VLF perturbations is less clear than that implied from the previous EuroSprite studies. In one storm that gave 20 sprites we found all to be accompanied with early VLF perturbations, whereas in a few other storms the number of the VLF events anticipated during the observed sprites, simply were not there. Here we present and discuss these findings, whereas we also provide some improved statistics on the early VLF event properties and discuss several correlative aspects by considering in addition to the VLF signatures the characteristics of the optical sprite images and those of the causative cloud to ground lightning discharges.

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The Sumatra tsunami induced ionospheric signatures from the CHAMP satellite: a manifestation of atmosphere-ionosphere coupling via

acoustic-gravity waves

E. Alam Kherani1, Philipp Lognonne2, Halen Herbert3 and G. Occhipinti4 1Instituto Nacional de Pesquisais Espaciais, Brazil ([email protected]) 2Institute de Physique du Globo du Paris, France

During the 24 December 2004 giant Sumatra tsunami, varieties of atmospheric and ionospheric signatures are detected. The low-orbiting CHAMP satellite has passed through this region many times in 2 hours interval and provided the electron density and magnetic variations at 400 km ionospheric heights. These data are very useful in understanding the tsunami induced fluctuations. They resides together with the fluctuations from other ionospheric sources and needs to be separated. Since the CHAMP satellite provides continuous observations (in 2 hours interval) of the Sumatra region before and after the event, it is possible to differentiate the tsunami induced fluctuations from others. The power spectrum distinctly shows the peak at certain frequencies during the event while these peaks remain absent on previous days. These frequencies are found below 10 mHz which indicates the possible involvement of Acoustic-gravity waves (AGWs) during the event.

To understand the possible cause of these fluctuations, we thus focus on the energy flow mechanism based on acoustic gravity waves. In this mechanism, AGWs are induced in the atmosphere by the sea surface displacement caused by the tsunami. These AGWs propagate to the ionosphere and gives rise to the current and subsequent fluctuations. The numerical simulation model is developed to deal with this process. In this model, the acoustic gravity wave equation and hydromagnetic equations are solved numerically. The results of this model is discussed in the context of observed fluctuations from the CHAMP satellite.



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Role of equatorial anomaly in assertion of low latitude earthquake-perturbations on ionosphere

M. Devi 1, A.K. Barbara 1, Yu. Ruzhin 2, A. Depueva 2, and V. Depuev 2

1: Department of Physics, Gauhati University, Guwahati 781 014, Assam, India ([email protected] ) 2: Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow region, Russia

The paper implicates a series of observations on ionization density (foF2) & TEC from ionosonde and GPS systems, to address the involution of equatorial anomaly in assertion of earthquake induced perturbations at the ionosphere. Adapting a pool of data acquired in this process around the equatorial anomaly crest stations, we bring in here the act of inducing low latitude seismic-related disturbances to off epicenter position, through anomaly effect when relative position between epicentre and observing station is (i) within the distance (d) dictated by the equation d = exp M (km), where M is magnitude of earthquake. We also examine (ii) cases when the radial distances exceed this limit.

The admission processes of earthquake preparatory effects in modifying ionospheric features are defined here in four temporal periods (pre-morning, noon, post noon, and post sunset) and symptoms on seismic-influenced anomaly effect are pulled out as precursor features. These characteristics are recorded on adopting filtering & screening approaches from quiet day parameters, individually for each defined time frame. The main predictor parameter obtained as “enhancement followed by depletion” in density and TEC, from a few days to the event days, are discussed invoking the role of seismic related E-field working with normal fountain processes. More than 20 earthquake events with radial distance defined as has been mentioned above are presented. For Guwahati, a seismically active area on Himalayan region, for the 13 cases (M≥5), the prediction is good.

For the case (ii), it is interesting to note that the above precursor characteristics are also recorded at the observing location, if a small magnitude earthquake (M = 4÷5) is present within the zone dictated by afore-said equation. The observation is presented through more than ten events. However the dynamical and physical processes are not yet clear.


Session S9: New techniques, experiments, campaigns, and results

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The New C/NOFS neutral wind instruments: laboratory and flight validation results

G. D. Earle1, J. H. Klenzing1, P. A. Roddy2, and E. L. Patrick3

1: William B. Hanson Center for Space Sciences, The University of Texas at Dallas, USA ([email protected]) 2: Air Force Research Laboratory, Hanscom AFB, USA 3: Southwest Research Institute, San Antonio, TX, USA

The US Air Force plans to launch the Communication/Navigation Outage Forecast System (C/NOFS) satellite in 2008, with the goal of establishing the feasibility of predicting the onset of equatorial spread F. Two of the sensors aboard the satellite have never before flown in a LEO environment, yet they are critical to overall mission success. Both sensors measure the bulk motion of the neutral gas in the spacecraft reference frame; the cross-track sensor (CTS) is designed to measure motions transverse to the satellite’s velocity, and the ram wind sensor (RWS) is designed to measure the velocity component along the orbit track. In this talk we present the results of validation tests for both sensors. For the CTS this comprises flight data from two suborbital sounding rocket flights, one of which was flown in conjunction with independent chemical release measurements from a companion rocket. Validating the capabilities of the RWS cannot be achieved via a sounding rocket, so a laboratory-based study was undertaken using a heated nozzle with argon and hydrogen gases in a free-jet expansion geometry. Results of both validation efforts will be presented in order to establish likely operational limits on the accuracy and sensitivity to be expected during the C/NOFS mission.

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COSMIC observations of the equatorial ionosphere

C. Coker1, K. F. Dymond1, S. A. Budzien1 and D. Chua1

1: Naval Research Laboratory, Washington, DC, USA ([email protected])

The FORMOSAT-3 Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is comprised of six spacecraft, each with three ionospheric sensors: GPS Occultation Experiment (GOX), Tri-Band Beacon (TBB) and Tiny Ionospheric Photometer (TIP). The concept of a multi-sensor, multi-satellite system provides unprecedented sampling of the ionosphere using both radio and optical techniques. The optical sensor TIP is a compact, narrow-band, ultraviolet photometer operating at the 135.6 nm wavelength. This emission is produced by recombination of O+ ions and electrons, which is the natural decay process for the ionosphere. The strength of the emission is proportional to the square of the peak electron density. The nadir directed photometers provide 15-30 km horizontal resolution of the nighttime ionosphere with sensitivity comparable to the radio sensors.

We present observations of the equatorial ionosphere obtained from the radio and optical sensors on COSMIC. All six satellites were deployed into a single high inclination, low-earth orbit. A single satellite pass reveals the latitudinal morphology of the ionosphere, with TBB and TIP providing horizontal information and GOX providing vertical information. This combination of sensors provides the opportunity to conduct multi-sensor investigations and high resolution imaging of low and midlatitude ionospheric structures. Observations from multiple spacecraft in the same orbital plane reveal the longitudinal variability of the ionosphere at a given local time. With the migration of the satellites into six longitudinally distributed orbits, the temporal variability of the ionosphere is observed, allowing for the



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investigation of the evolution of the ionosphere over specific longitudinal sectors, while providing a global picture of equatorial ionospheric variability.

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Coordinated UV imaging of equatorial plasma bubbles using TIMED/GUVI and DMSP/SSUSI

Joseph Comberiate 1 and Larry J. Paxton1

1 Johns Hopkins Applied Physics Laboratory, Laurel, MD ([email protected])

The Global Ultraviolet Imager (GUVI), launched on-board the TIMED satellite in December 2001, and the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) on board the DMSP F16 satellite launched in October 2003 have several overlapping years of observations of the nightside ionosphere. The low earth orbit of the DMSP and TIMED satellites allows for tomographic reconstruction of altitude vs. longitude bubble cross-sections from UV disk images. GUVI is at an altitude of 625 km in an orbit that precesses through all local solar times in just 60 days, and SSUSI is at an altitude of 830 km in a fixed 8AM/8PM local solar time orbit. We have developed a technique for tomographic retrievals of electron density profiles from GUVI observations. We discuss the adaptation of the tomographic imaging technique to SSUSI data and present initial results. Case studies of coincident and near-coincident GUVI and SSUSI plasma bubble images are also presented. Electron density profile reconstructions are accompanied by discussion and analysis of plasma bubble drift rates and changes in the morphology and tilt of bubbles as they drift through the ionosphere.

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Remote oxygen sensing by ionospheric excitation (ROSIE)

Konstantinos S. Kalogerakis1, Tom G. Slanger1, and Elizabeth A. Kendall2

1: Molecular Physics Laboratory, SRI International, Menlo Park, California, USA ([email protected]) 2: Center for Geospace Studies, SRI International, Menlo Park, Callifornia, USA

The principal optical observable resulting from ionospheric modification (IM) experiments is the oxygen red line at 630 nm, originating with the O(1D - 3P) transition. Because the O(1D) atom has a radiative lifetime of 110 s, it is very sensitive to collisional relaxation, and a decay faster than the radiative rate can be attributed to collisions with atmospheric particles. In contrast to the common practice of ignoring O-atoms in interpreting such observations in the past, our recent experimental studies on the relaxation of O(1D) by O(3P) have revealed the dominant role oxygen atoms play in controlling the lifetime of O(1D) at altitudes relevant to IM experiments. Using the most up-to-date rate coefficients for collisional relaxation of O(1D) by O, N2, and O2, it is now possible to analyze reliably the red line decays observed in IM experiments and thus probe the local O-atom density in the ionosphere. In this manner, we can demonstrate an innovative approach to remotely probe O-atoms at the altitudes relevant to IM experiments, test the current models for O-atom density in the ionosphere, and study its temporal, seasonal, altitude and spatial variation in the vicinity of heating facilities. We discuss the relevance to atmospheric observations and ionospheric heating experiments, report a preliminary analysis of data that have been accumulated from a number of IM sites, and present plans for more detailed collaborative studies in the future.



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Space-based studies of low-latitude ionospheric forcing originating in the lower atmosphere

T. J. Immel1, S.L. England1, J. M. Forbes2, J. D. Huba3, M. E. Hagan4, and R. DeMajistre5

1: University of California Berkeley, USA ([email protected]) 2: University of Colorado, Boulder, USA 3: Naval Research Laboratory, Washington DC, USA 4: High Altitude Observatory, Boulder, CO, USA 5: Applied Physics Laboratory, Laurel, MD, USA

A significant portion of the energy and momentum propagating upward from the lower and middle atmosphere to ionospheric heights is carried by atmospheric tides. Since most upward-propagating tidal waves dissipate in the lower ionosphere, their direct influence on neutral and ion conditions in the main F-layer might be expected to be small. Recently however, a strong correlation between modeled tidal amplitudes at 100 km and F-layer conditions (~350 km) at low latitudes has been clearly observed in global-scale ionospheric imaging from the IMAGE, TIMED, and COSMIC missions. The modulation of electric fields in the E-region dynamo by tidal driven winds was identified as one likely mechanism for extending tidal forcing above ~150 km. This theory has been tested with the TIMEGCM and SAMI models, confirming the importance of the dayside E-region dynamo and producing changes in modeled F-layer densities with magnitudes comparable to observations. The daytime equatorial electrojet current has also been found to exhibit a strong 4- peaked zonal variation in concert with the nighttime FUV morphology. These observations support the idea that structuring of the equatorial ionospheric anomaly originates in large part during the daytime buildup of plasma densities. Only recently, however, have the global tides themselves been compared to the observed ionospheric variations. Initial comparisons with mesospheric/lower-thermospheric temperatures from TIMED show the remarkable correspondence of tides with ionospheric effects, and co-variation on the timescales of weeks and seasons. Furthermore, the global ionospheric measurements carry indications of planetary wave modulation of tidal amplitudes on timescales too short to be retrieved from the space-based temperature measurements themselves. These observations mirror the findings of earlier ground-based studies using ionosondes, with the advantage of global observations providing the zonal wavelength of the affected tidal structures, complimenting the capability of the ground-based radars to provide the wave periods. These and other results point the way to important new collaborations between space- and ground-based research teams to understand the connection of terrestrial weather to geospace.

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Effects of non-ideal biased grids on geophysical parameters obtained from RPA data

J. H. Klenzing, G. D. Earle, R. A. Heelis, and W. R. Coley

William B. Hanson Center for Space Sciences, The University of Texas at Dallas, USA ([email protected])

The use of biased grids as energy filters for charged particles has been a common practice in satellite-borne instruments such as the retarding potential analyzer (RPA). The same method of analysis is also used in the ram wind sensor (RWS), an instrument in development by the Center for Space Sciences designed to measure the ram velocity component of the neutral wind. It has been shown previously that the use of biased grids in such instruments creates a non-uniform potential in the grid plane, which leads



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to errors in inferred geophysical parameters including velocity, temperature, and composition. A simulation of ion interactions with biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, perturbations to the idealized RPA equation are discussed with the intent of quantifying the inherent uncertainty of inferred parameters due to the non-ideal grids for current flight instruments.

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Plan of imaging observation of the mesosphere, ionosphere, and plasmasphere by ISS-IMAP mission

A. Saito and IMAP working group

Kyoto University, Kyoto, Japan

ISS-IMAP (Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping) mission will make the imaging observation of the Earth's upper atmosphere from the Exposed Facility of Japanese Experiment Module on the International Space Station (EF of ISS-JEM). It was selected as one of the five missions for the sharing-port mission of EF of ISS-JEM by Japan Aerospace Exploration Agency in December 2007. It is in the Phase-A study. The scheduled launch date is in 2011. The objective of this mission is to clarify the physical mechanism of the following three processes: (1) energy transport process by the atmospheric structures whose horizontal scale is 10-100km in the upper atmosphere (2) plasma transport process up to 20,000km altitude (3) effect of the upper atmosphere on the space-borne engineering system. ISS-IMAP will measure the following three parameters in the lower latitude region than 50 degrees: (1) distribution of the atmospheric gravity wave in the mesopause (87km), the ionospheric E-region (95km), and the ionospheric F-region (250km) (2) distribution of the ionized atmosphere in the ionospheric F-region (3) distribution of O+ and He+ ions in the ionosphere and plasmasphere. Two sets of imagers are designed for the ISS-IMAP scientific instruments. They are the visible imaging spectrometer instrument (VISI) and the extreme ultraviolet imager (EUVI). VISI will measure the airglow of 630nm [O], 650nm [OH], and 762nm [O2] in the Nadir direction. The altitudes of the emission layer are 250km, 87km, and 95km, respectively. Field-of-view (FOV) of VISI consists of two slits that is perpendicular to the orbital plane and width of 85 degrees. They direct forward and backward with 42 degrees of the angle from the nadir direction. EUVI will measure the resonant scattering of He+ in 30.4nm and O+ in 83.4nm. EUVI consists of two almost identical imagers. FOV of EUVI is 15 degrees for both wave length. It points the limb direction. In the presentation, the status of the ISS-IMAP mission, the scientific objectives, and instrument specification will be presented.

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The Low-latitude Ionospheric Sensor Network (LISN)

C. E. Valladares1, J. L. Chau2, J. V. Eccles3, and R. F. Woodman4

1: Boston College ([email protected]) 2: Chau, Jicamarca Radio Observatory 3: J. V. Eccles, Space Environment Corporation 4: R. F. Woodman, Instituto Geofisico del Peru

This paper describes the characteristics and illustrates the early measurements of the first distributed observatory that is being installed in the South American region to study the low-latitude ionosphere and upper atmosphere. The LISN distributed observatory will be comprised of nearly 70 GPS receivers with



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the capability to measure Total Electron Content (TEC), amplitude and phase scintillation and Traveling Ionospheric Disturbances (TIDs). The network will include 5 ionosondes able to measure nighttime E-region densities and 5 collocated magnetometers that will be placed along the same magnetic meridian. This network of GPS receivers and ionospheric sensors span from north to south in the South American continent and west of the 55o West meridian. They will complement each other to provide new, time continuous and spatially extended observations of the background ionosphere, its motion and the embedded structures over this large dynamic region.

The LISN network is being complemented with a physics-based data-inversion that incorporates a ionosphere model and a field-line-integrated electric field model to provide a consistent representation of the ionospheric electron density, conductivities, E×B plasma drifts, and neutral winds. This new distributed observatory will bring the opportunity to understand the day-to-day variability and the stability of the low-latitude ionosphere and to make forecasts on a regional basis. This paper describes the instrumentation, presents the first measurements and discusses the scientific benefits of the LISN network.

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Modeling the incoherent scatter radar spectrumperpendicular to r B

Marco Milla and Erhan Kudeki

Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign

50 MHz Jicamarca radar is being used to make F-region incoherent scatter (IS) spectrum measurements with antenna beams pointed perpendicular to the Earth’s magnetic field. Such measurements are possible on a pulse-to-pulse basis (as opposed to ACF measurements conducted with multi-pulse procedures) because the incoherent scatter Doppler spectrum narrows down considerably at small magnetic aspect angles, i.e., when a narrow radar beam is pointed perpendicular to the geomagnetic field. In fact, the measured spectra are even narrower than theoretical predictions based on collisionless F-region models and it was recognized only recently by Sulzer and González [1999] that Coulomb collisions need to be included to have a better agreement of the theory with the data. The same paper also introduced a numerical modeling procedure for collisional IS spectra at small but non-zero aspect angles.

Fitting or inverting the measured Jicamarca spectra obtained with perpendicular to r B radar beams

requires a collisional forward model valid for zero magnetic aspect angle. We describe here how we have developed such a model and present some preliminary examples of data inversions obtained with it. Our model effectively extends the procedure of Sulzer and González [1999] into three dimensions and derives the electron and ion Gordeyev integrals from random 3D trajectories simulated for charged particles embedded in a magnetized plasma with suppressed collective interactions. The trajectories are randomized by Coulomb collisions as described by the Fokker-Planck equation of Rosenbluth et al. [1957], or, equivalently, by a generalized Langevin equation with velocity dependent friction and diffusion coefficients. A statistical analysis of the simulated trajectories shows that ion motions are well modeled by a Brownian motion process (with constant friction and diffusion coefficients), and therefore an analytical expression for the ion Gordeyev integral can be obtained as outlined in Woodman [1967]. However, simulated electron motions do not fit a Brownian model and a numerical library of electron Gordeyev integrals had to be developed for an oxygen plasma. The library spans a set of densities, temperatures, and magnetic fields as needed for Jicamarca F-region applications. The electron and ion Gordeyev integrals are then utilized in standard IS models [e.g., Kudeki and Milla, 2006] for producing theoretical IS spectra to be fitted to Jicamarca observations.



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References: Kudeki, E., and M. Milla, Incoherent scatter spectrum theory for modes propagating perpendicular to the geomagnetic field, Journal of Geophysical Research, 111, 1–3, 2006. Rosenbluth, M. N., W. M. MacDonald, and D. L. Judd, Fokker-planck equation for an inverse-square force, Physical Review, 107, 1–6, 1957. Sulzer, M. P., and S. A. González, The effect of electron Coulomb collisions on the incoherent scatter spectrum in the F region at Jicamarca, Journal of Geophysical Research, 104, 22,535–22,551, 1999. Woodman, R. F., Incoherent scattering of electromagnetic waves by a plasma, Ph.D. thesis, Harvard University, Cambridge, Massachusetts, 1967.

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Full profile incoherent scatter analysis at Jicamarca

D. L. Hysell1, F. S. Rodrigues1, J. L. Chau2, and J. D. Huba3

1: Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA ([email protected]) 2: Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima, Peru 3: Plasma Physics Division, Naval Research Laboratory, Washington, DC, USA

Incoherent scatter data from a hybrid long-pulse/double-pulse experiment at Jicamarca are analyzed using a full-profile analysis, whereby plasma density, electron and ion temperatures and light ion composition profiles are estimated simultaneously in the topside. Such an analysis is crucial at Jicamarca, where the long correlation time of the incoherent scatter signal invalidates conventional gated analysis. Results from experiments in 2006 and 2007 are presented and compared with results from the NRL ionospheric model SAMI2. The analysis provides the first comprehensive assessment of ionospheric conditions over Jicamarca at sunrise as well as the first 24-hour record of helium ion layers. Possible refinements to the experiment and the algorithm are discussed.

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Incoherent scatter measurements of F-region temperatures with the Jicamarca radar beam pointing perpendicular to B

P. Reyes, M. Milla, and E. Kudeki

Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Illinois, USA ([email protected])

The availability of a new incoherent scatter (IS) spectrum model for radar measurements perpendicular to the Earth's magnetic field [e.g., Milla and Kudeki, 2008] is giving us the opportunity to revisit the problem of estimating F-region temperatures with the Jicamarca radar beam pointing in this direction. Previously, Kudeki et al. [1999] examined the problem based on a collision-less IS model and inferred electron temperatures (not reported) about half of what was expected. This was because the measured IS spectra were narrower than what the collision-less theory predicted. The same year Sulzer and González [1999] recognized that the incorporation of Coulomb collisions into the theory would account for spectral narrowing even though their proposed collisional model did not extend to perpendicular to

r B viewing

geometry. We expect the new spectral theory of Milla and Kudeki [2008], that extends the effect of



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collisions to all magnetic aspect angles, to fit the data accurately enough so that we can estimate realistic F-region temperatures with Jicamarca measurements.

In a typical perpendicular to r B Jicamarca experiment, the radar beam covers a range of magnetic

aspect angles going from zero to about a degree, a range in which the IS spectrum sharpens quite rapidly. As a result, the beam-weighted spectrum measured by the radar is composed of a narrow peak that corresponds to the signal scattered from the close vicinity of perpendicular to

r B , and a wide aliased

component corresponding to the contributions away from perpendicularity. While the wide aliased component increases with both the electron temperature Te and the ratino of electron and ion temperatures Te Ti , the peak narrows down with Te . Furthermore the overall spectra power increases with Te Ti . However, because the wide component is essentially frequency aliased, estimation of both temperatures from a single spectrum is not straightforward. In order to improve the accuracy of the overall temperature estimation, we have configured the north and south quarters of the Jicamarca array as an interferometer. In this configuration, the phase of the cross-spectrum present a very sensitive linear dependence on Te and almost independent on the ion temperature Ti . Under these considerations, the self-spectrum and cross-spectrum constitute a better set of data that makes the estimation problem better conditioned. Here, we report on both the modeling of the beam-weighted IS spectrum and cross-spectrum measured with the Jicamarca radar, and the inversion technique used in the estimation of electron and ion temperatures at F-region heights

Rerefences

Erhan Kudeki, Santanu Bhattacharya, and Ronald F. Woodman. A new approach in incoherent scatter F region E × B drift measurements at Jicamarca. Journal of Geophysical Research, 104(A12):28145–28162, December 1999.

Marco A. Milla and Erhan Kudeki. Modeling of the incoherent scatter spectrum perpendicular to b. In 12th International Symposium on Equatorial, May 2008.

M. P. Sulzer and Sixto A. González. The effect of electron Coulomb collisions on the incoherent scatter spectrum in the F region at Jicamarca. Journal of Geophysical Research, 104(A10):22535–22551, October 1999.

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Recent progress in studying equatorial and low-latitude irregularities with Equatorial Atmosphere Radar

T. Yokoyama1, M. Yamamoto2, Y. Otsuka3, A. K. Patra4, S.-Y. Su5, S. Fukao2, and D. L. Hysell1

1: Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, USA 2: Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan 3: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan 4: National Atmospheric Research Laboratory, Tirupati, India 5: Institute of Space Science, National Central University, Chung-Li, Taiwan

The 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20ºS, 100.32ºE, -10.14º dip latitude) has the unique capability of rapid beam scanning on a pulse-to-pulse basis. EAR can take a snapshot of backscatter echoes with zonal and altitude distances of several hundred kilometers within a few minutes. Since the first operation of EAR in 2001, many important aspects, for example, onset, growth and spatial distribution of equatorial spread F, have been revealed with EAR and presented in the last ISEA meeting. We will focus on the following subjects studied in recent years.



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(1) Weak irregularities are observed in the valley region (120-160km altitudes) in the post-sunset period. These echoes have similar horizontal structure to that of F-region plumes and propagate eastward with the same velocity. (2) Plasma blobs detected by ROCSAT-1 in the northern hemisphere coincided with the resurgence of radar plumes. The zonal structure and upward drift velocity of the blobs correspond to those of the plumes on the common magnetic flux tube. These two results suggest strong electrodynamical coupling between E and F regions, and northern and southern hemispheres. (3) While the occurrence of post-sunset spread F decreases in the low solar activity period, post-midnight irregularities have been frequently observed with EAR. The characteristics of these echoes are similar to the midlatitude spread F observed with MU radar rather than equatorial spread F. They propagate westward with a structure aligned from northeast to southwest. (4) Daytime 150-km echoes are detected with EAR. The major characteristics are common to those observed in the equatorial regions. On the other hand, the echo intensity in the east-west plane is not uniform but has strong asymmetry that is opposite to equatorial observations. Because the EAR location is in transition between equatorial and midlatitude region, the EAR is an important tool to study latitudinal coupling as well as vertical coupling.

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First results on studies of the low latitude ionosphere with the CITRIS beacon receiver on STPSAT1

Carl L. Siefring and Paul A. Bernhardt

Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 ([email protected])

The Scintillation and TEC Receiver in Space (CITRIS) instrument is the newest ionospheric remote sensing sensor in space. The CITRIS receiver is one of two instruments on the United States Space Test Program STPSAT1 satellite which was launched 8 March 2007. CITRIS is in a 35° inclination orbit at an altitude of 560 km so that its measurements are focused on the low-latitude ionosphere. The CITRIS receiver is designed to lock onto low-earth-orbit (LEO) beacons such as Tri-Band-Beacon/CERTO on COSMIC, CERTO on DMSP/F15, VHF/UHF on NIMS and ground UHF/S-Band beacons that comprise the DORIS system. CITRIS operates in radio frequency bands near 150, 400, 1066 2/3 MHz, and 2036.25 MHz to obtain total electron content (TEC) and radio scintillation parameters. Full details of CITRIS have been published by Bernhardt et al. [2006].

For most of the operations with LEO beacons, the CITRIS data collection is scheduled to use beacons on orbits that have conjunctions with the CITRIS satellite within a few kilometers. Out to ranges of 6000 km the CITRIS receiver tracks the radio signals from the beacon satellites at VHF (150 MHz), UHF (400 MHz), and, when available, L-Band (1066 2/

3 MHz). At large ranges, the TEC measurements provide limb scanning profiles of the ionosphere to the west and east of the minimum distance conjunction points for the satellites. Linear regression of the TEC versus distance between satellites allows absolute calibration of the TEC data using zero TEC is obtained for zero inter-satellite distance. With this technique, the absolute TEC between beacon and receiver can be determined within 0.1 and 0.01 TEC Units (1016 m-3). In addition the phase and amplitude of the VHF, UHF and L-Band waves are analyzed to yield radio scintillation parameters Using the satellite-to-satellite measurement technique, up to 48 independent TEC scans over 21000 km range can be obtained from the CITRIS data set. Most of the CITRIS measurement data are obtained over the ocean or remote regions of the earth where ground based observations are rare.

The other mode for CITRIS is to recorded TEC and radio scintillations from the 56 ground radio beacons that are part of the French DORIS network. DORIS radiates ultra-stable radio waves at 401.25



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and 2036.25 MHz. From these signals CITRIS obtains TEC and radio amplitude at a rate of 200 samples per second. The density of DORIS beacons is large enough that there is almost always one DORIS beacon in view of the CITRIS receiver. Up to 56 separate scans of TEC and UHF scintillations are obtained per day with CITRIS. CITRIS observations with ground beacons near incoherent scatter radars, such as the Arequipa DORIS beacon near the Jicamarca radar in Peru, provide spatial scans of equatorial irregularities that can be compared with structures that drift through the radar beam.

Bernhardt, PA. and C.L. Siefring, I.J. Galysh, T.F. Rodilosso, D.E. Koch, T.L. MacDonald, M.R. Wilkens, G.P. Landis, Ionospheric Applications of the Scintillation and Tomography Receiver in Space (CITRIS) used with the DORIS Radio Beacon Network, J. Geodesy, 80, 473-485, 2006.

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New optical experiments for studying equatorial irregularities

Jonathan J. Makela1, John W. Meriwether2, Ethan S. Miller1, and Shaun J. Armstrong1

1:Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 2:Department of Physics and Astronomy, Clemson University, Clemson, SC, USA

A new narrowfield imaging system, the Portable Ionospheric Camera and Small Scale Observatory (PICASSO), was installed at the Cerro Tololo Inter-American Observatory (geographic: 30.17 S, 289.19 E; geomagnetic 16.72 S, 0.42 E) near La Sarena, Chile in August 2006. The imaging system, pointed towards the northern horizon, obtains high-resolution images of the ionosphere through the observation of the 630.0- and 777.4-nm emissions and provides excellent data on the spatio-temporal development of equatorial plasma bubbles (EPBs) associated with equatorial spread-F. The wide field-of-view in the longitudinal direction of approximately 2000 km at F-layer altitudes allows the simultaneous observation of multiple EPBs as they drift through the field of view, from which we can deduce the inter-bubble spacing which should be related to the underlying seeding mechanism. In addition, we present examples on how the images obtained from the southern hemisphere can be used with corollary instruments in the conjugate hemisphere to deduce additional properties of equatorial irregularities, such as the altitude of the scattering layer. Another new experiment is being set up in the African sector as part of the International Heliospherical Year (IHY). The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) consists of two different types of optical instruments, a wide-angle version of the PICASSO imaging system installed in Chile, and two miniaturized Fabry-Perot Interferometers (MiniME). The wide-field imaging system will be used to characterize the two-dimensional (latitude vs longitude) structure of the depletions. This will be done by measuring the natural emissions occurring in the ionosphere at wavelengths of 630.0 and 777.4 nm. The two FPI systems will be used to measure the background thermospheric neutral winds and the neutral temperature. From the FPI data, we will be able to deduce what, if any, control neutral dynamics have on the development of these irregularities. Two systems are included so we can field them at sites separated by several hundreds of kilometers in order to study wind gradients and gravity waves known to be present in the thermosphere. The instruments will enable studying thermosphere-ionosphere coupling during the passage of EPBs as well as the effects of the background neutral wind field on the development of EPBs. We present results from the two MiniME systems during their pre-deployment testing phase and discuss the technique developed for analyzing the multiple orders obtained from the MiniMEs.



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A thermospheric lidar for He 1083 nm, density and Doppler measurements

G. Swenson1, C. Carlson1, L. Waldrop1, and P. Dragic1

1: University of Illinois, Champaign-Urbana, Illinois ([email protected])

Thermospheric lidar offers a new and powerful means to obtain the temperature measurements needed to resolve many fundamental open questions of thermospheric physics. Metastable Helium atoms, which are created in the upper thermosphere via photoelectron impact on ground-state He atoms, are well-suited as targets for thermospheric lidar owing to their large resonant scattering cross section at 1083 nm. Gerrard et al. [1997] modelled and simulated the concept of a 1083 nm resonant scattering lidar for the possibility of studying Doppler winds and temperatures from the 250-700 km altitude region. The University of Illinois Remote Sensing group has developed the key technological element now enabling 1083 nm lidar measurements: a 50 W, CW, solid-state, narrow band (<1 MHz) laser, capable of being tuned to measure the Doppler broadened distribution at 1083 nm. Modelling has been extended to develop simulations of signal returns for twilight metastable populations for low latitude stations including Arecibo, PR and Jicamarca, Peru. The simulations as well as instrumental concepts will be described.

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WIND rocket campaign: Lithium release experiment in evening midlatitude thermosphere

M.-Y. Yamamoto1, Y. Yokoyama1, H. Habu2, T. Abe2, S. Watanabe3, M. Yamamoto4, Y. Otsuka5, A. Saito4, T. Ono6, and M. Nakamura2

1: Kochi University of Technology, Kochi, Japan ([email protected]) 2: Japan Aerospace Exploration Agency, Kanagawa, Japan 3: Hokkaido University, Sapporo, Japan 4: Kyoto University, Kyoto, Japan 5: Nagoya University, Nagoya, Japan 6: Tohoku University, Sendai, Japan

On September 2, 2007, as the WIND rocket campaign, the JAXA’s S-520-23 sounding rocket was launched from Uchinoura, Japan (131.08 E, 31.25 N) in order to investigate interaction of neutral and plasma atmosphere in midlatitude thermosphere especially in the evening condition of generating MSTID (Medium-Scale Travelling Ionospheric Disturbances). Main purpose of our experiment is to establish a new technology of chemical release in the thermosphere. In the WIND experiment, thermospheric neutral wind profile was measured by sequential images of 670.8 nm resonance scattering luminescence of Lithium. Three chemical releases at 230 km, 193 km, and 144 km altitudes were successfully carried out by newly developed LES (Lithium Ejection System), resulting successful triangulation from 4 independent ground sites.

The red luminescence of Lithium was clearly observed. At the beginning of 1st release, luminescence intensity more than 1 M rayleigh was observed by 125 g Lithium injection. As a preliminary result of the thermospheric neutral winds at 4 altitudes, SE-ward wind of 80 m/s or more at 250 km, SSW-ward 100 m/s wind at 200 km, SSW-ward 80 m/s wind at 150 km, and NNE-ward 60 m/s wind at 120 km were obtained, respectively. It is also found that the obtained neutral wind profile had strong wind shear in the altitude range between 120 km and 150 km. Observed initial rate of Lithium diffusion speed of 3.2 km/s at 250 km was comparable to theoretical thermal diffusion speed of 3.67 km/s in a temperature condition of 1600 K (near the boiling temperature of Lithium). Though flight velocity of the rocket itself



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might affect on the motion of Lithium vapor until about 150 s after the release, neutral wind could be derived from the sequential images sufficiently after their merging process into surrounding atmosphere.

From the ground-based GPS-TEC observations over Japan, it was in initial state of evolving the MSTID at the exact experimental period. The SE-ward neutral wind at 250 km coincides with required condition of evolving Perkins instability in the interesting altitude range of MSTID. In this talk, the neutral wind velocity profile and the Lithium diffusion in wide altitude range in the thermosphere will be discussed in detail.


Session S10: Ionospheric storms and space weather effects

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The United Nations and International Committee on Global Navigation Satellite Systems: World-wide ground-based instrument arrays

Sharafat Gadimova

Office for Outer Space Affairs, United Nations Office at Vienna, Austria

Following the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III), held in 1999, the United Nations General Assembly endorsed the “Vienna Declaration: Space Millennium for Human Development.” The Vienna Declaration called for action to improve the world–wide use of global navigation satellite systems (GNSS) for a societal benefits and economical growth, including research on climate change and the composition of the atmosphere. Since 2004 the world-wide ground-based instrument arrays for exploring atmospheric phenomena related to space weather and climate change are being established. Within the framework of an international committee on GNSS (ICG), which was established as an informal body for the purpose of promoting the use of GNSS infrastructure on a global basis and to facilitate exchange of information, GPS applications in low-cost world-wide ground based instrument arrays will be considered.

During the International Heliophysical Year, coordinated investigation programmes utilizing space- and ground-based observatories have been organized to study universal processes at work throughout the solar system. Maximum use will be made of the Internet and World Wide Web infrastructure to facilitate communication and organization. These research campaigns will operate in a similar way to the Solar and Heliospheric Observatory’s Joint Observing Projects. The resulting data sets will be processed and assembled in order to make them readily available to the global science community. Coordinated data analysis will be performed during a series of workshops and the results will be published and made available to the science community.

Individuals within the research community may participate in coordinated investigation programmes. Discipline coordinators will review all suggestions and organize similar coordinated investigation programmes (CIPs) into observing programmes that can be implemented. Observatory coordinators representing each of the instruments participating in the International Heliophysical Year will assist in this process. Later, the observing programmes will be organized into cross-disciplinary topical universal process workshops to discuss and communicate the scientific results of the International Heliophysical Year campaigns.

Reference:

N. Gopalswamy and R. Ramesh (Eds.), Proceedings of the Second UN/NASA Workshop on International Heliophysical Year and Basic Space Science, Bulletin of the Astronomical Society of India, 35 (2007) 415-758.

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Ionospheric storm fronts at low and mid latitudes

J. C. Foster1

1: MIT Haystack Observatory, Westford, Massachusetts, USA ([email protected])

In the early phases of large geomagnetic storms the low and mid-latitude ionosphere are greatly perturbed. Discrete storm fronts of enhanced ionospheric plasma at low and mid latitudes are produced in a two-stage process which spans the inner and outer regions of the ionosphere-magnetosphere system. The particular configuration of the magnetic field at low latitudes in the Atlantic sector creates a preferred



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longitude/Universal Time sector (western Atlantic/ 21 UT) for the build-up of significantly enhanced TEC on field lines inside the dusk plasmapause. At the plasmasphere boundary layer (PBL), the sub-auroral polarization stream electric field (SAPS) forms as pressure gradients at the inner edge of the magnetospheric ring current drive Region-2 field-aligned currents into the evening-sector ionosphere. Large poleward-directed electric fields at ionospheric heights are set up to drive closure currents across the low-conductivity region equatorward of the auroral electron precipitation. The inward extent of the SAPS overlaps and erodes the outer plasmasphere and mid-latitude ionosphere, drawing out extended plumes of storm enhanced density (SED) which span the dusk sector, transporting ionospheric and outer-plasmaspheric material to the noontime cusp and onto polar cap field lines.

At low latitudes, a combination of stormtime penetration electric fields, the effect of the reduced magnetic field strength in the South Atlantic magnetic anomaly, and the geographic distortion of the magnetic field in the Atlantic sector contribute to a unique set of characteristics of the low-latitude polarization electric fields at the sunset terminator. At dusk, polarization electric field effects begin at a given point in the ionosphere when the E region at either end of the magnetic field line through that point begins to go into darkness. We define the polarization terminator (PT) to be the locus of points at a given altitude for which the E-region shadow height at either end of the magnetic field line equals 100 km. Electric fields associated with the charge build-up in the E-region conductivity-gradient region due to the effects of winds or penetration electric fields are directed perpendicular to the PT and increase in magnitude as the PT is approached from the dayside. In the Atlantic sector, the electric fields at low latitudes along the PT have significant poleward as well as eastward components resulting in a westward and poleward redistribution of the plasmas at the crests of the equatorial ionization anomalies. This low-latitude plasma is swept onto field lines in the plasmasphere boundary layer which are overlapped by the SAPS electric field. The redistribution of the low-latitude ionosphere by the dusk sector PT creates an enhanced source population of high-TED plasma which feeds into the high total content storm enhanced density (SED) plumes observed during strong storms in the American sector.

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The solar wind control of the equatorial ionosphere dynamics during geomagnetic storms

L. Biktash1, T. Maruyama2, and K. Nozaki2

1: Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Acad. Sciences (IZMIRAN), Troitsk, Moscow region, 142190, Russia ([email protected]) 2: National Institute of Information and Communications Technology (NICT),4-2-1, Nukui- Kitamchi, Koganey, Tokyo 184-8795, Japan, e-mail: [email protected]

The interplanetary magnetic field, geomagnetic variations, virtual ionosphere height h'F and the critical frequency foF2 data during the geomagnetic storms are studied to demonstrate relationships between these phenomena. We study 5-min ionospheric variations using the first Western Pacific Ionosphere Campaign (1998 - 1999) observations, 5-min interplanetary magnetic field (IMF) and 5-min auroral electrojets data during a moderate geomagnetic storm. The ionospheric 5-min variations at the equatorial stations which allow calculating in detail time delays of the auroral and equatorial ionospheric phenomena are scantily known. These data allowed us to demonstrate that the auroral and the equatorial ionospheric phenomena are developed practically simultaneously. Hourly average of the ionospheric foF2 and h'F variations at near equatorial stations during a similar storm show the same behavior. We suppouse this is due to interaction between electric fields of the auroral and the equatorial ionosphere during geomagnetic storms. It is shown that the low-latitude ionosphere dynamics during these moderate storms



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was defined by the southward direction of the Bz-component of the interplanetary magnetic field. A southward IMF produces the Region 1 and Region 2 the field-aligned currents (FAC) and polar electrojet current systems. We assume that the short-term ionospheric variations during geomagnetic storms can be explained mainly by the electric field of the FAC. The electric fields of the field-aligned currents can penetrate throughout the mid-latitude ionosphere to the equator and may serve as a coupling agent between the auroral and the equatorial ionosphere. The storm wind driven electric fields which responsible for the larger amplitudes and longer lifetimes of the drift perturbations are discussed. It is shown that model simulations as disturbed ionospheric wind dynamo d o not allow explaining a significant part of the experimental data. Additional investigations of the ionospheric characteristics are required to clear up the origin of the short-term equatorial ionospheric variations.

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Low latitude ionospheric effects of major geomagnetic storms observed using TOPEX TEC data

Y.O. Migoya Orué 1, S. M. Radicella 2 and P. Coïsson 2

1: CIASUR – FRT – Universidad Tecnologica Nacional, Tucumán, Argentina 2: ARPL, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

The low latitude ionospheric effects of two major geomagnetic storms are analysed using TOPEX TEC data for specific satellite passes. The storms are the one that started on 15 July 2000 (daily F 10.7 = 226.1, R = 197.0, maximum Dst = -301; values for 16 July 2000) and the one that started on 8 November 2004 (daily F 10.7 =121.7, R = 57.0, maximum Dst = -373; values for 8 November 2004). The variation of TEC as a function of latitude along the satellite passes during day-time and night-time mostly in the region of the Pacific Ocean have been analysed comparing the storm period with quiet conditions. It has to be noted that for obvious reasons the TEC behaviour over this region cannot be observed using ground-based instruments but TOPEX data can give a reasonable overall view of the region covered by the Equatorial Anomaly. Approximately the same geographical area and local time storm conditions were considered. The results show that, during day-time, the Equatorial Anomaly TEC peaks move towards the poles by several degrees and increases their intensity by roughly a factor of three with respect to the quiet conditions behaviour. This is seen for both storms that occurred at different seasons and solar activity level. The night-time storm effect appears less defined and more complex. Clear examples of TOPEX passes showing these findings are shown and discussed.

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Vertical distribution of electron density derived from TEC data of the GRACE satellite and the ground-based GPS receivers at

mid- and low-latitudes

Yukari Goi１, Akinori Saito1, Michi Nishioka1, and Takuya Tsugawa2

1: Kyoto University, Kyoto, Japan ([email protected]) 2: National Institute of Information and Communications Technology (NICT), Tokyo, Japan

Variations of Total Electron Content (TEC) in the upper ionosphere and the plasmasphere were studied using TEC data observed by the GRACE satellite and the ground-based GPS receivers. The GPS receiver



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on the GRACE satellite measured the dual-frequency of the GPS radio wave to detect the precise location of the satellite. TEC between the GRACE satellite and the GPS satellites (GRACE-TEC) was derived from this GPS data. The altitude of the GRACE satellite was from 450km to 500 km. Therefore, the GRACE-TEC data consist of TEC of the upper ionosphere and the plasmasphere. Several types of GRACE-TEC variations were detected at mid- and low- latitudes. In the low-latitude region, Equatorial Ionization Anomaly (EIA) was frequently seen in the GRACE-TEC data. During geomagnetically quiet periods, single peak of GRACE-TEC was observed on the geomagnetic equator. This peak is attributed to EIA. During geomagnetically disturbed periods, double peaks of GRACE-TEC were frequently observed at low-latitudes. The enhanced storm time eastward electric field raised the ionosphere up to the high altitude on the equator. Thus, GRACE-TEC above 450 km altitude showed the double peaks of EIA. At mid-latitudes, three types of GRACE-TEC variations were observed. They are TEC enhancement, TEC depletion, and TEC boundary. GRACE-TEC enhancement was observed at 20:48UT on 29 May 2003 over the American sector. Storm Enhanced Density (SED) was detected by the ground-based GPS receiver at the same time. The location of GRACE-TEC enhancement and SED was coincident. That is, the GRACE satellite observed the TEC enhancement of the topside of SED. The enhancement of GRACE-TEC in SED was about 10 TEC units. This large increase of GRACE-TEC indicates that intense electron density enhancement occurred above 450 km altitude inside of the SED. The vertical distributions of electron density for the other mid- and low-latitude phenomena were analyzed with GRACE-TEC and ground-based TEC data.

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Some consequences of stormtime, global energy budgets

William J. Burke

Boston College and AFRL/RBXP, Hanscom AFB, MA 01731

Neutral mass densities ρ measured by the CHAMP and GRACE satellites, joined with information readily available from ACE at L1 and ground magnetometers, offer new opportunities to monitor the energetics of the magnetosphere-ionosphere-thermosphere system during magnetic storms. This presentation uses measurements of ρ from the GRACE satellite to drive Jacchia thermospheric models. Within the tables of the Jacchia model we identify internal quadratic relationships between ρ and exospheric temperatures T∞. We then demonstrate that T∞ is linearly related to Eth the total (gravitational and thermal) energy of the thermosphere. Further analysis shows that stormtime increases of Eth exceed, by a factor of four, the ring current’s energy estimated via the Dessler-Parker-Sckopke theorem. Thus, most stormtime energy deposition occurs at polar cap rather than auroral latitudes. This result profoundly affects understanding of the disturbance dynamo’s genesis.

Eth has two independent but additive contributions from solar ultraviolet radiation (EUV) and the solar wind (ESW). Up to now the dynamics of EUV are modeled better. During storms ESW evolves as a

driven-dissipative system: SW SWM

dE E = αE - dt τ

where EM is the driving magnetospheric electric field; α

and τ are empirically established coupling and relaxation constants. The observed e-fold decay constant τ ≈ 6.5 hours is mostly due to infrared radiative losses. EM is estimated from routine ACE measurements. Similar equations describe the solar-wind’s contributions to T∞SW and the Dst index. Solving these simultaneous equations offer the possibility of estimating ESW, T∞SW, and EM during storms when interplanetary measurements are unavailable.



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Ionospheric and magnetic field effects observed during the 2005 geomagnetic storms in the South-East Asian sector

Alina Marie Hasbi1,2 , Mohd Alauddin Mohd Ali 1,2, and Norbahiah Misran1,2

1: Electrical, Electronic and Systems Department, Faculty of Engineering, University Kebangsaan Malaysia, Malaysia ([email protected], [email protected]) 2: Institute of Space Science, Universiti Kebangsaan Malaysia, Malaysia

This paper presents the investigation of geomagnetic storm effects on the equatorial ionosphere in the South-East Asian region during two major storms in 2005. We represent the two geomagnetic storm events as Storm-A that occurred on 15 May 2005 (SSC at 0300 UT and Dstmin= -263 nT at 0300 UT on 15 May; ΣKp=44; Apmax=105; Bzmin= -44.81 nT) and Storm-B that occurred on 24 August 2005 (SSC at 0600 UT and Dstmin= -216 nT at 1100 UT on 24 August; ΣKp=48; Apmax=110; Bzmin= -55.40 nT). The interplanetary magnetic field Bz component is southwardly directed for about 3 hours indicating the formation of a storm. Simultaneous ionospheric TEC and scintillation measurements were recorded using five equatorial latitude ground-based GPS receiver stations in Malaysia and Indonesia to analyze storm properties from 14 to 17 May 2005 for Storm-A and 23 to 26 August 2005 for Storm-B. Geomagnetic field data obtained from three MAGDAS and INTERMAGNET equatorial latitude stations in South-East Asia as well as global IMF and solar wind data from MFI/SWE instruments onboard the ACE spacecraft are used to corroborate GPS-TEC variations during the storm period. Our results show that intense geomagnetic storms can perturb the ionosphere significantly at equatorial latitudes. During Storm-A, TEC exhibits enhancement features only; a TEC increase of 98% relative to the mean quiet day during the storm’s main phase and a maximum value of 96.86 TECU. Meanwhile, TEC during Storm-B exhibits enhancement-depletion features; a maximum enhancement of 150% with respect to the mean quiet day during the storm’s main phase on 24 August 2005, a maximum value of about 65 TECU and a depletion of about 40% relative to the mean quiet day which lasted for 6 hours during the recovery phase on 25 August 2005. Pronounced phase scintillation, S4 index of value close to 1.0 as well as strong Pc4 pulsations with amplitude exceeding 30 nT prevailed during the main and recovery phases of the storm. This study also shows that magnetic H, D and Z component variations are in good agreement with TEC variations.

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A comparative analysis of mid-latitude storm-time ionospheric peak parameters variability

D. Buresova1, J. Lastovicka1, L-A. McKinnell2, T. Sindelarova1, and D. Novotna1

1: Institute of Atnospheric Physics, Prague, Czech Republic ([email protected]) 2: Hermanus Geomagnetic Observatory, Hermanus, South Africa

Ionospheric variability is one of the most interesting and still insufficiently explored behaviour. The interest in ionospheric variability is stimulated partly by unresolved physical issues variability presents, and also by necessity to improve models of the ionosphere. Variety of processes in work under severe space weather conditions makes it much harder to forecast the ionospheric response. In the present study we report the results of a comparative analysis of the observed ionospheric peak parameters with International Reference Ionosphere (IRI-2001) and global foF2 model during strong-to-severe ionospheric storms that occurred in the period 1995-2006 over the Southern and Northern Hemisphere middle



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latitudes. Recently the IRI2001 model incorporated a geomagnetic activity dependence based on an empirical Storm-Time Ionospheric Correction Model (STORM). To perform a detailed comparison between observed values, medians and model-generated values the correlation coefficient, the normalised root-mean-square error (NRMSE), and the percentage improvement are calculated. The comparative analysis illustrates that the improved IRI-2001 model with the activated STORM option provides better description of the ionisation distribution under geomagnetic storm conditions. The STORM model captures more effectively the negative phases of the ionospheric storms, nevertheless, electron density enhancement and changeover of the different storm phases is reproduced with lower accuracy. Model corrections are less efficient for lower-middle latitudes and severe geomagnetic storms. As STORM model makes no storm-time corrections of hmF2, the correlation coefficient during storm main phase ranges between 0,3-0,7. Results for the prediction of foF2 during storm-time periods by the global foF2 model were also generated. In addition to the alternation of the sign of the storm effect, there are some other problems broader investigations of them are still needed. Among acute ones are, e.g. enhancements of electron density sometimes observed several hours before the onset of geomagnetic storm. We have analysed a couple of such events.

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New insights into prompt penetrating electric fields

M. C. Kelley1 and J. Retterer2

1: Cornell University, Ithaca, NY, USA ([email protected]) 2: Air Force Research Laboratory, Hanscom AFB, MA, USA

The series of strong magnetic storms in the last several years has allowed new insights into prompt penetrating electric fields (PPE). Both November storms in 2003 and 2004 had excellent radar coverage. The local time dependence of the PPE in the Peruvian sector has been clarified and examples will be presented. Also to be discussed are the suppression and triggering of convective equatorial ionospheric storms (CEIS) by PPE in one of these events, along with its successful prediction using a numerical model.

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On the relationship between interplanetary electric fields (IEF) and equatorial-electroject (EEJ).

C. Manoj1,2,3 , S. Maus1,2, and H. Lühr 4

1.CIRES, University of Colorado, ([email protected]) 2.National Geophysical Data center, NOAA 3. National Geophysical Research Institute, Hyderabad 4. GeoForschungsZentrum Potsdam

Prompt penetration of the interplanetary electric field (IEF) to the mid and low latitude ionosphere is well documented (Nishida 1968, Kikuchi et al. 1996). This effect was believed to last only up to ~30 minutes due to a shielding effect by the Region 2 current system, which requires some time for adjustment. However, recent studies (Huang et al., 2005, Kelley at al., 2007) report that the Prompt Penetrating Field can be present for longer durations (up to 10 hours) in the low-latitude ionosphere. Due to the sporadic nature of radar-based ionospheric electric field and/or magnetic field measurements, most of these studies were event based. Hence the frequency dependence of the low latitude electric field penetration to the IEF



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input is not fully understood. Comparing six years of ionospheric drift measurements at the low latitude JULIA radar with interplanetary solar wind and magnetic field measurements from the ACE satellite, we estimate a coherence spectrum between IEF and the equatorial drift velocities. The large dataset allows investigating the seasonal and local time dependence of the penetration effect. We also investigate the coherence of IEF with polar-cap-potential index (PC), sub-auroral and equatorial geomagnetic data.

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Morphology of quiet-time F2-layer disturbances at geomagnetic equator

A.H. Depueva, A.V. Mikhailov, and V.H. Depuev

Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region 142190, Russia ([email protected])

Ionospheric F2-layer disturbances not related to geomagnetic activity (Q-disturbances) were analyzed using all available NmF2 observations over Huancayo (American sector) and Kodaikanal (Indian sector) stations located at the proximity of geomagnetic equator. Both positive and negative Q-disturbances were revealed, their amplitude being comparable to usual F2-layer storm effects. The occurrence of Q-disturbances exhibits a systematic dependence on solar activity, season, and local time. Contrary to middle latitudes, negative Q-disturbances are more numerous compared to positive ones at both stations and all levels of solar activity. Long duration (≥ 3 h) disturbances are more numerous at solar minimum compared to solar maximum. The majority of negative long duration disturbances occur in the dark LT sector and they are practically absent during daytime hours. Positive long duration Q-disturbances exhibit two occurrence maxima – the nighttime-early-morning and the daytime ones. Annual variations for the occurrence of both negative and positive Q-disturbances at Huancayo exhibit a well-pronounced pattern with the occurrence maximizing in winter for all solar activity levels. On the contrary, daytime positive Q-disturbances at Huancayo are observed only in summer. At Kodaikanal annual variations for the occurrence are not distinct, although there is a tendency for a distribution with winter and summer maxima. The revealed morphology of Q-disturbances at Huancayo can be related to the observed at Jicamarca ExB vertical drifts. There are some differences between Huancayo and Kodaikanal Q-disturbance morphological patterns which cannot be attributed to small differences in ExB vertical drifts in the two longitudinal sectors.

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Large-scale traveling ionospheric disturbances observed by GPS receiver networks!

T. Tsugawa1, K. Shiokawa2, H. Hayashi2, N. Nishitani2, Y. Otsuka2, T. Ogawa2, J. Lei3, and A. Saito4!

1: National Institute of Information and Communications Technology, Koganei, Tokyo, Japan ([email protected]) 2: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi, Japan 3: High Altitude Observatory, National Center for Atmospheric Research, Colorado, USA 4: Department of Geophysics, Graduate School of Science, Kyoto University, Japan!

We report recent observations of large-scale traveling ionospheric disturbances (LSTIDs) using GPS receiver networks. LSTIDs generally have horizontal wavelengths of more than 1,000 km and periods of 30-180 min. They are believed to be ionospheric manifestations of the passage of atmospheric gravity waves that are generated at high latitudes by energy input from the magnetosphere. Dense GPS receiver



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networks in Japan (GEONET: GPS Earth Observation Network System) can provide high-resolution total electron content (TEC) maps that reveal precise spatial structure and temporal evolution of LSTIDs. Time sequences of these TEC maps give reliable wave parameters, such as wavelength, propagation velocity, direction, period, amplitude, and damping rate. Geomagnetic conjugate observations of LSTIDs between the northern and southern hemispheres revealed their non-conjugacy. On December 15, 2006, a prominent northward propagating LSTID has been observed by the GEONET and the SuperDARN Hokkaido HF radar in Japan. Comparison between the observations and the CMIT model simulation indicates that it propagated from the high latitudes of the southern hemisphere into the northern hemisphere over Japan. Statistical study of LSTIDs over Japan revealed that they can be observed even under quiet conditions. These quiet-time LSTIDs are often observed in winter and in the daytime. Their equatorward propagation direction and the seasonal and local-time variations of their occurrence are consistent with those of daytime medium-scale TIDs (MSTIDs) detected with dense and wide TEC maps over North America. The quiet-time LSTIDs and the daytime MSTIDs may be the same ionospheric phenomena.

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Large scale TIDs observed in GPS derived differential TEC

C. Borries, N. Jakowski, and V. Wilken

DLR, Institute of Communications and Navigation, Neustrelitz ([email protected])

In this study we focus on deriving measures of the activity of wavelike perturbation processes in the ionosphere, called Travelling Ionospheric Disturbances (TIDs). The TID activity has a significant impact on the accuracy and reliability of precise Global Positioning System (GPS) reference network applications. Because of its dual frequency, signals received from GPS satellites enable extracting information of the dispersive ionosphere. The European area is covered with dense networks of GPS receivers providing data with frequencies of 1/30 to 1Hz. The good data coverage of more than 150 ground stations enables calculating maps of the ionospheric disturbance activity with high accuracy. It is shown that in the course of several storms significant wave packets may be generated at high latitudes. These waves are assigned to large scale TIDs propagating equatorwards. Typical wave parameters such as velocity, wave length and direction can be estimated from the maps. The results support recent findings by other authors. In this study, additionally ionospheric radio occultation data will be used to detect the proven large scale TIDs. The differential TEC derived from low earth orbiting satellites is supposed to reveal information about the vertical spreading of these TIDs.

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IGW and electric field effects in the topside equatorial ionosphere

A.T. Karpachev

IZMIRAN, Troitsk, Moscow region, Russia ([email protected])

Internal gravity waves, IGW, and electric field effects in the topside ionosphere are considered from the ground-based and satellite sounding data for the several substorms. The (a)symmetry of the ionospheric response on the IGW passage depending on the local time and season is studied. It is shown that during the strong substorm in the equinoctial conditions the wave front is continuous and covers all longitudes, latitudes and altitudes of the topside ionosphere. During the moderate substorm the IGW effects appear



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mainly in the night-time ionosphere, the disturbed area gets narrow to the equator and the stronger wave from the winter hemisphere passes through the equator up to low latitudes of the summer hemisphere. During the weak substorm traveling ionospheric disturbance, TID, arrive at the equator only in the winter night-time ionosphere sector where the source of the disturbance was strong. The effects of the IGW and electric field of the ionospheric and magnetospheric origin were divided. The effect of the “fast ionospheric dynamo” was revealed. The propagation of the fast wave (very likely MHD wave) was observed. The IGW impact on the EA structure in the whole (including Ne, hmF2 and crest position variations) is considered.

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A new ionospheric forecast model assimilating solar wind data and ground based ionosonde observations

I. Tsagouri, K. Koutroumbas, and A. Belehaki

National Observatory of Athens, P. Penteli, Greece ([email protected])

The development of ionospheric forecasting methods is still a challenging research field that undergoes continuous evolution with the introduction of new scientific results. Based on recent advances in ionospheric storm dynamics that correlate the ionospheric storm effects with interplanetary magnetic field parameters such as its magnitude and its orientation in the north-south direction and the availability of these parameters in real time by the ACE spacecraft from the vantage L1 point, a new ionospheric forecasting method was recently introduced. The proposed method is based on the fusion of two diverse techniques: i) an autoregression forecasting algorithm capable for real time ionospheric predictions up to 24 hours ahead during all possible ionospheric conditions, namely Time Series AutoRegressive (TSAR) model and ii) an empirical storm time ionospheric model (STIM) for predicting the onset and for scaling ionospheric response during geomagnetic storms based on the solar wind parameters, providing ionospheric predictions up to 40 hours ahead. The cooperation of the two methods introduces the Solar Wind driven autoregression model for Ionospheric short term Forecast (SWIF), which presents clear advantages since it is capable to provide alerts and warnings for impending ionospheric disturbances as well as ionospheric forecasts for prediction horizon significantly greater than 24 hours ahead. Validation tests are also carried out to verify the reliability of SWIF’s estimates over Europe.

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Specification of ionospheric dynamics at low- and mid- latitudes using a physics-based data assimilation model

L. Scherliess, D.C. Thompson, and R.W. Schunk

Center for Atmospheric and Space Sciences, Utah State University, Logan, USA ([email protected])

It is well known that the ionosphere-plasmasphere-thermosphere system at low and middle latitudes is strongly coupled, and therefore, a study of ionospheric dynamics must take into account the interaction between the different domains. As shown by meteorologists and oceanographers, a powerful way of modeling complex systems is with the use of data assimilation models. We have developed two data assimilation models with different complexity and both provide global and regional specifications of the 3-dimensional ionosphere-plasmasphere plasma densities. One of these models is a Full Physics-Based Kalman filter data assimilation model, which is based on a physics-based model for the ionosphere-



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plasmasphere system, a diverse array of data sources, and an ensemble Kalman filter data assimilation technique. This model covers the ionosphere-plasmasphere system from 90 30,000 km altitude and includes 6 ion species (NO+, N2

+, O2+, O+, He+, H+) and needs to be run on a cluster of ~30 CPU

workstations. The strength of this model is that in addition to the global and regional 3-D ionosphere electron density distribution it also self-consistently determines the corresponding ionospheric drivers, including the thermospheric neutral winds and the low-latitude electric fields. The model can assimilate a variety of different data types, including GPS/TEC from hundreds of ground receivers, in situ Ne from several DMSP satellites, bottomside Ne profiles from tens of ionosondes, and occultation data from the six COSMIC satellites. We have used this model to study the dynamics of the low- and mid-latitude ionosphere during geomagnetically quiet and disturbed times over the American, Asian, and European sector, where ground-based ionospheric observations are abundant. The model was used on a case-by-case basis to determine the various driving forces and to study their temporal and spatial variability. We will present examples of the ionospheric and driver specifications obtained from our model runs with an emphasis on geomagnetically disturbed periods and compare our results with independent data.


Poster P4: Posters for Session S9 (New techniques, experiments, campaigns, and results)

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New development of digital beacon receiver based on GNU Radio

M. Yamamoto

Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Kyoto, Japan ([email protected])

The total electron content (TEC) of the ionosphere can be measured by means of the radio beacon experiment from low-earth orbit (LEO) satellites. We measure two or three frequency signals on the ground, and determine phase difference between the signals that is proportional to the TEC along the propagation pass. This is an old technique, but is still useful especially with the radio tomography observations. Advantage of the LEO satellite-beacon experiment over the GPS-TEC experiment is that it observes TEC of the ionosphere only, and each pass of the satellite is much faster. Several recent satellites like FORMOSAT-3/COSMIC and C/NOFS have tri-band beacon transmitters on board. Progress of the digital signal processing now makes it possible for us to assemble VHF/UHF receivers based on the software defined radio (SDR) technique. In this study we developed a new 2-frequency (150/400 MHz) digital beacon receiver system based on GNU Radio which is a free software toolkit for the SDR on LINUX (http://www.gnu.org/software/gnuradio/), and the Universal Software Radio Peripheral (USRP) that is the general-purpose digital transceiver board. Hardware development for the beacon receiver is limited to antenna, pre-amplifiers, and filters. Software is divided into ‘digital receiver program’, ‘observation scheduling and control program’ and ‘data analysis program’. Test of the digital receiver was conducted on August 31 and September 1, 2007 at JAXA/USC (Uchinoura Space Center). Fortunately a well-developed analog beacon receiver, CIDR (Coherent Ionosphere Doppler Receiver) from University of Texas at Austin, was operated at the same location. Comparison of TEC over four passes of FORMOSAT-3/COSMIC satellites proved that our measurements were successful. In the presentation we will show design of the beacon receiver, data analysis for TEC derivation, results from test observations, and future plan of the experiment. Finally we note that our receiver is much inexpensive compared to the commercial systems, and design information and software for the receiver is open to everybody.

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The Vector Electric Field Instrument on the C/NOFS Satellite

R. Pfaff1, J. Kujawski1, P. Uribe1, K. Bromund1, R. Fourre1, M. Acuña1, G. Le1, W. Farrell1, R. Holzworth2, M. McCarthy2, and D. Rowland1

1: NASA/Goddard Space Flight Center, Greenbelt, MD, USA ([email protected]) 2: Univ. of Washington, Seattle, WA, USA

We provide an overview of the Vector Electric Field Instrument (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. VEFI is a NASA GSFC instrument designed 1) to investigate the role of the ambient electric fields in initiating nighttime ionospheric density depletions and turbulence; 2) to determine the electric fields associated with abrupt, large amplitude, density depletions and 3) to quantify the spectrum of the wave electric fields and plasma densities (irregularities) associated with density depletions or Equatorial Spread-F. The VEFI instrument includes a vector electric field double probe detector, a Langmuir trigger probe, a flux gate magnetometer, a lightning detector and associated electronics. The heart of the instrument is the set of double probe detectors designed to measure DC and AC electric fields using 6 identical, mutually orthogonal,



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deployable 9.5 m booms tipped with 10 cm diameter spheres containing embedded preamplifiers. A description of the instrument and its sensors will be presented. If available, representative measurements will be provided.

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Paired Ionosphere-Thermosphere Orbiters (PITO): A general-purpose science mission with high capability

J. Clemmons

The Aerospace Corporation

A mission that is capable of addressing many science topics in the realm of ionosphere-thermosphere physics is described and discussed. The mission utilizes a pair of orbiting vehicles in eccentric, high-inclination, coplanar orbits. The orbits have arguments of perigee that differ by 180 degrees and are phased such that one vehicle is at perigee (200 km) while the second is at apogee (2000 km). Half an orbit later, the vehicles switch positions. Three types of science instruments are envisioned to take advantage of this scenario: those that measure local, in-situ parameters, downlooking imagers that view areas, and vertical profiling instruments. The main idea is that in addition to the two-point measurements provided by the in-situ instrumentation, context information for the low-altitude measurements is obtained by the high-altitude imagers. In addition, profiling instruments such as sounders and spaceborne lidar can be added to create vertical profiles. Such an observation system is capable of providing elements of global coverage, regional coverage, and resolution in three dimensions. Presented are candidate orbits, strawman instrument suites, approximate mission resource needs, and expected science targets.

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The Precision Expandable Radar Calibration Sphere (PERCS) for improvement of the HF radar accuracy

P. A. Bernhardt

Plasma Physics Division, Naval Research Laboratory, Washington, DC

HF radars are used to detect ionospheric irregularities, meteor trails and other moving geophysical targets. The Doppler frequency shifts provides the velocity of the moving objects. The time delay is interpreted to give the range to the reflection point taking into account the refraction of the ionosphere. The amplitude of the radar echo provides information on the size and aspect orientation of the target. All of these parameters rely on precise calibration of the HF radar. Up to now, however, there has never been an orbiting satellite designed specifically for HF radar calibration.

The Precision Expandable Radar Calibration Sphere (PERCS), scheduled for launch in 2010 or 2011, will provide a relatively simple target in space that can be used to determine the operational parameters of ground HF radars. PERCS will have a known radar cross section that is independent of observation direction within 0.5 dB. The orbital position and velocity of PERCS will be known to within one meter. The anticipated altitude of PERCS will be 500 km to that there is sufficient echo from the target for radar detection. The inclination should be over 80 degrees so that HF radars at all latitudes can use the target sphere. The computed radar cross section for the sphere is 25 dBm2 (300 square meters) with a few dB frequency dependent variations. This cross section is large enough to be usable with most ground based HF radar systems.



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The PERCS satellite will be launched in a stowed configuration that has less than one meter in diameter. After launch, the PERCS will expand to a diameter of over 10 meters. Hoberman Sphere technology will be used to produce a stable wire-frame to act as a radar scatter target. After examining a number of polyhedron structures for the wire frame, the chosen design is a 180-vertex sphere is based on a truncated Rhombic Triacontahedron. The 180 vertices are intersection points to 270 edges. Each edge is composed of hinged scissors so that the PERCS can be folded into a compact package for launch. The total sphere has 360 hubs and 1620 links to form the transformable structure. The mass of the sphere is estimated to be 160 km with 6 mm diameter links. Each of the 80 hexagon faces and 12 pentagon faces are uncovered so that the orbiting sphere has low atmospheric drag. At an altitude of 500 km, the PERCS sphere will be in orbit more than 800 days.

Analysis of the V180 wire frame with a 10.2 meter diameter shows that the radar cross section (RCS) is independent of viewing angle up to 36 MHz. In addition, there is a VHF window at 50 MHz where the backscatter cross section is independent of orientation. This makes it ideal for calibration of SuperDARN radars in the 8 to 20 MHz range as well as the meteor and E- and F-region radars near 30 and 50 MHz. The PERCS target is also invaluable for checking the antenna patterns for ionospheric heating facilities such as HAARP, EISCAT Heating and the new Arecibo HF Facility. Radar performance will be measured or validated using the radar echo data and the precise knowledge of the target RCS, position, and velocity. The wire frame structure has several advantages over a metalized spheroid “balloon” with (1) much less drag, (2) large radar cross section, and (3) low fabrication cost. After PERCS is launched, the international HF radar community for HF studies will greatly benefit by having a target the can yield radar return signal strength measurements in absolute, not relative, units.

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A new nitric oxide detector with absorption cells driven by a fast cam system

P. Muralikrishna

Instituto Nacional de Pesquisas Espaciais, S. J. Campos-SP, Brazil ([email protected])

A nitric oxide (NO) detector, making use of a newly designed fast cam-driven absorption cell system is being developed for launch on board sounding rockets, to measure the height profile of the NO gamma band day glow emission intensity and thereby to estimate the height profile of the number density of atmospheric NO in the equatorial region. Two absorption cells, one of them containing the gas NO and the other nitrogen are brought in front of the photocathode of a photomultiplier (PM) tube alternately using a cam system. Each cell remains in front of the PM tube for an interval of time fixed by the cam shape. In conventional NO detectors the absorption cells are mounted either on a rotating wheel or are moved by a cam system controlled by a step motor. In the new mechanical system presented here the movement of the cam is controlled by curve segments on a circular disc, that are cycloids of the form ϕϕ sin.dry −= designed to optimize the time needed for positioning the cells one after the other and also to make smooth the operation of the step motor responsible for the movement of the absorption cells. The cycloidal form was chosen for the cam profile after analyzing the mechanical performance characteristics of various other types of curves. The major advantage of the cycloid is the smooth variation of the gradient along it from one point to another. The gradient is what decides the motor torque needed for the movement of the shaft along the cam profile. Thus a smooth variation in the gradient guarantees smooth variation in the motor torque. The advantages of this new system over the conventional wheel mounting are also presented.



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GEO-6 project and Czech participation in

D. Kouba, J. Lastovicka, J. Boska, D. Buresova, P. Sauli, and Z. Mosna

Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic ([email protected])

GEO-6 project “Scientific research Using GNSS” is a joint project of seven institutions from six countries led by the AtosOrigin company from Spain. Its aim is to propose and broaden scientific utilization of future GNSS Galileo system. The core of the project consists from six projects in five priority areas: PA-1 Remote sensing of the ocean using GNSS reflections, PA-2a Investigating GNSS ionospheric data assimilation, PA-2b 3-D gravity wave detection and determination (both PA-2a and PA-2b are ionospheric topics), PA-3 Demonstration of capability for operational forecasting of atmospheric delays, PA-4 GNSS seismometer, PA-5 Spacecraft formation flying using global navigation satellite systems. Institute of Atmospheric Physics, Prague, Czech Republic is responsible for PA-2b. The paper will present basic description of the project with more details concerning Czech participation.

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Longitudinal variation of the low-latitude ionosphere observed by FORMOSAT-3/COSMIC

C. H. Lin1, H. F. Tsai2, C. H. Chen3, J. Y. Liu3, and C. H. Liu4

1: Plasma and Space Sciences Center, National Cheng-Kung University, Tainan, Taiwan ([email protected]) 2: Central Weather Bureau, Taipei, Taiwan 3: Institute of Space Science, National Central University, Chung-Li, Taiwan 4: Academia Sinica, Taipei, Taiwan

This study presents longitudinal structure of the low-latitude and equatorial ionosphere using the radio occultation observation of the FORMOSAT-3/COSMIC. The structure is believed to be formed due to modification of the daily dynamo electric field at regions where lower atmospheric tides are generated by latent heat release of the tropical rain storms. Changes of the dynamo electric field result in modification of the equatorial plasma fountain and the equatorial ionization anomaly (EIA). With capacity of three-dimensional global ionospheric observations, altitude ranges, local times, and monthly variations of the fascinating feature are obtained. The feature is identified at and above F-region ionosphere during 1000-2200 LT periods. A four-peaked structure is shown during March-April and August-October, while a three-peaked structure is seen during November-February. The structure is less prominent in May and June. The longitudinal structure may result from atmospheric tides in different wave modes. We also examine the corresponding wave modes of the resulting ionospheric structures.



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Continual 24-hour observations of thermospheric winds and temperatures made with the Second-generation Optimized Fabry-Perot Doppler Imager

(SOFDI)

A. J. Gerrard1 and J. W. Meriwether2

1: New Jersey Institute of Technology, New Jersey, USA ([email protected]) 2: Clemson University, South Carolina, USA

The Second generation Optimized Fabry-Perot Doppler Imager (SOFDI), a state-of-the-art triple-etalon Fabry-Perot interferometer, has been constructed, tested, and is now making continual 24-hour observations in upstate New York. The 630 nm data, originating from layer-integrated OI emission with centroid heights of 250 km at night and 220 km during the day, are analyzed so as to obtain measurements of horizontal winds and temperatures in the thermosphere. In this paper we report the most recent results from continuous 24-hour observations of these thermospheric parameters.

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Evaluation of topside equatorial spread F spectra estimators using Monte Carlo simulations

F. R. Galindo1, K. M. Kuyeng1, J. L. Chau1, and D. L. Hysell2

1: Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima 2: Department of Earth and Atmospheric Sciences, Cornell University, USA

Monte Carlo simulations of typical echoes from equatorial ionospheric irregularities as well as ground clutter are used to evaluate different aperiodic pulsing and inversion techniques. Our main objective is the estimation of the moderately overspread topside equatorial spread F (ESF) spectra where using typical periodic pulsing schemes the spectra is typically aliased if one wants to avoid range aliasing. In this work we evaluate different aperiodic pulsing as well as inversion (e.g., periodogram, Lagrange interpolation, Maximum Entropy, Gaussian Fitting,…) schemes to estimate the spectra (or its corresponding autocorrelation function (ACF)). In particular we will evaluate the pros and cons of using sequences with small and large interpulse period variations. Depending on the nature of the spectra, we will also evaluate the optimal spacing and number of pulses needed. The optimal spectra estimators combined with radar imaging techniques might represent the unique means to estimate the irregularity power and energy spectral density versus wavenumber from the ground.

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Dagik: Data-showcase system to browse multi aeronomy data in four-dimension

A. Saito1 and D. Yoshida1

1: Kyoto University, Kyoto, Japan

Dagik (DAily Geospace data In Kml) is a system to display multi-data of the geospace. It uses Google Earth as a data browser, and enables to show the data in four-dimension. Several data of the aeronomy are now available on Dagik. They are: global TEC maps by MIT/Haystack and JPL, regional TEC maps over



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Japan, EISCAT radar data, Hokkaido SuperDARN radar data, All-sky imager network data by Nagoya University, IMAGE satellite FUV image, ionosonde data in Japan by NICT, ion density data of the DMSP satellite, geomagnetic indices, and others. The motivation of Dagik is so-called “data problem”. The number of observations and the amount of the data has drastically increased in a few decades. As the number of geophysical data increased, it got widely recognized that it is important but difficult to combine the various type of data. Although World Wide Web (WWW)-based databases of geophysical data have enhanced the data exchange since middle of 1990s, it is not easy for scientists to compare and combine data with WWW-based databases. Meta-databases, such as virtual observatory projects, are one of proposed solutions to solve this “data problem”. We propose a system to show various types of geophysical data in four-dimension with real relative scale. It showcases the quicklook plot of data, and is used as a portal to the databases. Dagik (http://www-step.kugi.kyoto-u.ac.jp/dagik/) started as a data-showcase in March 2007. The more aernomy data plot is available on Dagik, the more Dagik get useful. In the presentation, the system and examples of Dagik will be introduced. We expect to develop Dagik as a science support system with feedback from the various researchers.

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Observing the spatial characteristics of TIDs with broadband HF direction finding

S. Hawlitschka

FGAN-FKIE/SDF, Wachtberg, Germany ([email protected])

Over the last years a narrow-band HF super-resolution direction finding (DF) system has been used to investigate the temporal characteristics of Traveling Ionospheric Disturbances (TIDs) at mid-latitudes. The wavelike processes were well visible in temporal variations of the azimuth of radio stations with known location. Now broad band HF super-resolution direction finding (DF) data have been used to compare the signatures of ionospheric waves at different locations. The data were acquired using the Broadband Automatic HF-Monitoring System BRAHMS which is capable to receive and store up to 4-6 MHz bandwidth continuously with 10 coherent channels. Several data sets have been recorded, covering the complete 49 m radio band for a duration of 15 h or covering the complete 41 m and the 49 m radioband with a duration of more than 4 h. The directions of the emitters were calculated using super-resolution DF algorithms such as MUSIC. The time series of the azimuth of selected emitters were analysed and compared to the time series of other emitters with different location. Thus an investigation of spatial characteristics of medium-scale ionospheric irregularities was possible. The results have been compared with simulated azimuth diagrams via a pattern recognition process. The simulations have been conducted via ray-tracing the HF waves in an disturbed ionosphere. The parameters of the simulated TIDs have been varied to match the characteristics of the observed azimuth data.

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Installation of an ionospheric station in Cyprus

H. Haralambous, G. Dekoulis, and P. Vryonides

Frederick University, 7 Y. Frederickou Str., Palouriotisa,1036 Nicosia, Cyprus

A major research initiative has been undertaken at Frederick University to establish ionospheric research in Cyprus. The foundation of this effort is the installation and operation of a fully automated DPS-4D (digisonde) developed at the University of Massachusetts Lowell’s Center for Atmospheric Research



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(UMLCAR). The deployment of the station is considered very beneficial to the ionospheric scientific community, taking into account the lack of adequate scientific infrastructure, especially at low latitudes of the European sector, for continuous ionospheric monitoring. Its operation will contribute to international networks for nowcasting and forecasting space weather effects to the Earth’s ionosphere and to the enhancement and validation of ionospheric models in the eastern Mediterranean region.

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Monitoring of ionospheric weather over Cyprus and Egypt

H. Haralambous 1, A. Mahrous 2 , P. Vryonides 1, A. Shemis 2

1: Frederick University Cyprus Frederick University,7 Y. Frederickou Str., Palouriotisa,1036 Nicosia, Cyprus 2: Helwan University Egypt

The primary objective of the initiative is to establish an ionospheric monitoring network over Cyprus and Egypt by linking the corresponding instruments in operation in the two countries: a group of three Coherent Ionospheric Doppler Receiver (CIDR) systems being deployed in a roughly north-south chain in Egypt and a modern digital DPS-4D digisonde in Cyprus. The results and the subsequent analysis of observations from coordinated measurement campaigns will aid towards improved understanding of the upper atmosphere environment over the eastern Mediterranean region and especially of ionospheric irregularities over a significant latitudinal extent also enhancing the knowledge on the coupling mechanisms between mid-latitude and low-latitude ionosphere. The cooperation in the frames of the proposal between the two countries is considered very beneficial especially taking into account the fact that both countries lack important infrastructure and a tradition of ionospheric observations.An unusual night time ionospheric phenomenon observed at Tucumán, Argentina, under quiet geomagnetic conditions

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An unusual night time ionospheric phenomenon observed at Tucumán, Argentina, under quiet geomagnetic conditions

S. M. Radicella 1, L. Ciraolo 2, M. Mosert 3, O. Abarca 3, B. Zolesi 4, M. Pezzopane 4 , R. Ezquer 5, and M. Cabrera 5

1: ARPL, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy 2: IFAC-CNR, Firenze, Italy 3: CASLEO-CONICET, San Juan, Argentina 4: Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy 5: CIASUR – FRT – Universidad Tecnologica Nacional, Tucumán, Argentina

An Advanced Ionospheric Sounder, built at the Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, was installed at Tucumán, Argentina, (Lat 26.5 S, Long 64.7 W, Dip -26) particularly interesting for its location, under the southern peak of the ionospheric equatorial anomaly. Both the ionograms and the basic ionospheric characteristics automatically scaled are available real-time on line. An unusual phenomenon was observed on October 1st, 2007 at night, a period geomagnetically quiet. After few hours of low values foF2 risen to 8.7 MHz at 6.00 UT corresponding to 2.00 LT. to decrease in two hours to below 2 MHz. Measurements of total electron content (TEC) taken at locations near Tucumán and to the north toward the geomagnetic equator allowed to study the evolution of TEC in the region during the phenomenon and to calculate the slab thickness above Tucumán. The variations of this parameter during that night were unusual because it dropped to a value of



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119 km at 2.15 LT but risen to 713 km at 4.30 UT to drop again to 238 km at 7.15 LT. These observations are confirmed by the analysis of the electron density profiles obtained from the Tucumán ionograms. They allow a careful description of the movements of ionization and expansions and contractions of the ionosphere in the region of the southern peak of the equatorial anomaly over South America difficult to explain.

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Comparisons between the observed electron density profile at the equatorial station of Ilorin, Nigeria, and the IRI model

O.A. Oladipo 1, S.M. Radicella 2, and J.O. Adeniyi 1

1:Physics Department, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria 2:ARPL, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

This study compares the observed average equatorial electron density profiles N (h) with the profiles predicted by IRI-2001 model using the two available options (B0 Table option and Gulyaeva’s option. Ionograms recorded at Ilorin, Nigeria with geographic coordinates 8.53 °N, 4.57 °E and Magnetic dip 4.1 °S were used. Only available and reliable data for January 2002 with monthly average Rz number of 114.1 and January 2006 with monthly average Rz number of 15.3 were used. For each hour both the average monthly electron density values and the corresponding standard deviation were calculated every ten kilometers of altitude up to the maximum electron density in the F2 region. The investigation is concentrated on the daytime hours (0700 LT - 1700 LT). The results confirm previous results about the electron density variability as a function of heights. It must be noted that a well-defined F1 observed at low solar activity (2006) during several hours around noon is not reproduced by either options of the model. In addition the results showed that Gulyaeva’s option underestimates electron density at all heights for the two months. While B0 Table option underestimates at F1 heights but overestimates at F2 heights for the two months. In general, B0 Table option’s prediction gives a better agreement with observation at all heights for hours around the noontime.

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Total electron content over South America usign LISN GPS data: 2007 climatology and special events

E. Silvestre1, J. Valverde1, P. Condor1, O. Veliz1, and C.Vallladares2

1: Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima,Perú 2: Boston College, Boston, USA

Since January 2007 more than 20 GPS dual-frequency receivers have been in operations as part of the Low-latitude Ionospheric Sensor (LISN) network in South America (SA). By July 2008, we expect the network to be fully operational consisting of more than 50 GPS dual frequency receivers, 5 digital ionosondes and 5 magnetometers. In this work we present preliminary total electron content (TEC) results using one year of data from 25 stations covering different latitudes and longitudes en SA. First we concentrate on the diurnal characteristics for different seasons and magnetic activity for the the different sites (and therefore latitudes and longitudes). Such climatology is compared to the TEC estimates from the latest International Reference Ionosphere (IRI) model, and to the digisonde inferred TEC values at Jicamarca. In the latter comparison GPS data from Jicamarca and/or Ancon are used. In addition two



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special events are studied in detail and compared to the climatology, i.e., the storm events of December 16th, 2007 and January 8th, 2008. Besides the TEC from GPS, for these storm events, we also make use of magnetometer data from one located under the magnetic equator (Jicamarca) and one outside the equatorial electrojet region (Piura), allowing us to get a proxy meausurement of the ExB F region drift velocity. This preliminary work, represents one of the many type of results that we expect to get with the fully operational LISN network in a much better and more reprsentative way.

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Ground observation of ionospheric scintillation and TEC within EEJ borders

A. B. Rabiu1, K. Groves2, R. S. Fayose1,3, and O. R. Bello1

1: Space Physics Lab., Dept. of Physics, Federal University of Tech., AKURE, Nigeria. ([email protected]) 2: Space Weather Center of Excellence, AFRL/VSBXI, Hanscom AFB, MA, USA. 3: Department of Physics, Adekunle Ajasin University, Akungba Akoko, Nigeria

Scintillation Network Decision Aid (SCINDA) is a real-time, data driven, communication outage forecast and alert system. Its purpose is to aid in the specification and prediction of communication degradation due to ionospheric scintillation in the equatorial region of Earth. Ultra high frequency (UHF) and L-band scintillation parameters are measured, modeled and propagated in time to provide a regional specification of the scintillation environment in an effort to mitigate the impacts on the satellite communications community. Equipment at the remote sites record scintillation parameters from available UHF Fleet Satellite Communication System and L-band (Geostationary Operational Environmental Satellite (GOES), GPS) satellite links and measure ionospheric drift velocities. SCINDA consists of a set of ground-based sensors and quasi-empirical models, developed to provide real-time alerts and short-term (< 1 hour) forecasts of scintillation impacts on UHF satellite communication and L-Band GPS signals in the Earth's equatorial regions. The SCINDA system concept is presently being demonstrated using ten equatorial stations in South America, South Asia and West Africa. Preliminary results of studies of ionospheric scintillations and total electron content within the equatorial electrojet are discussed. Response of the two parameters within the rising and setting hours of the Sun is discussed.

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Low elevation measurements of GPS ocean reflections

P. Høeg1, X. Yin1, L. Olsen1, and A. Carlström2

1: Aalborg University, Aalborg, Denmark ([email protected]) 2: Saab Space, Gothenburg, Sweden

GPS ocean reflected signals describe the height and roughness of the ocean as well as characteristics of the troposphere. The signal is weak, but still able to establish experimental knowledge on the influence of signal multi-path interference and signal disturbances caused by the atmosphere and the surroundings. We present results from GPS ocean reflection measurements made at the Haleakala summit on Maui, Hawaii, during October 2004. The altitude of the observation site (above 3000 meters) gave a long free line-of-sight view over the ocean to the horizon.

The characteristics of the reflected signal depend on the scattering properties of the sea surface and the footprint of the reflection. The footprint size and shape in turn depends on the signals incidence angle and the relative velocities of transmitter and receiver to the reflection point. The scattering properties of the sea surface are related to the roughness, which depends on sea wave characteristics. We



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present the spectral properties of the signals as received by the high precision GPS instrument, simultaneously in both phase-locked mode (PL) and open-loop mode (OL) in separate receiver channels. The instrument software has been modified for ground based signal Doppler conditions, driven by an ultra-stable rubidium frequency reference to control the receiver clock for precise timing of the measurements. The OL mode provides the in-phase and quadrature components of the signal at a sample rate of 1000 Hz, which enables investigation of spectral signatures that are normally not seen in standard GPS data. This includes effects of various sources of multi-path and atmospheric turbulence. The instrument setup consists of separate L1 and L2 antennas both oriented with the main gain lobe toward the horizon. The use of directive antennas pointed towards the horizon enables signal recordings down to the lowest layers of the atmosphere. The experiment showed valuable information on GPS signal tracking under severe disturbed tropical conditions such as multi-path interference, moist troposphere strong variations and low signal intensity. Direct determination of ocean altitudes is limited to reflected signals at higher elevations. The accuracy of a mean ocean surface is of the order of a few wavelengths. For low elevation grazing GPS signals, a radio occultation retrieval technique has been applied. The results are compared with a statistical retrieval method, named low-complexity track-before-detection (TBD), where the retrieval algorithms are based on a particle filtering approach, which in total can be view as a sequential Bayesian estimation method. We present the results from the different retrieval techniques and discuss the advantages of the TBD method for determining the ocean height and roughness parameter.

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Some results of the GPS Tec observations in the southeast Asian region

M. Le Huy1, R. Fleury2, P. L. Duchesne2, A. Bourdillon3, C. Amory-Mazaudier4, T. N. Chien1, and L. Tran Thi1

1: Institute of Geophysics, Vietnamese Academy of Science and Technology, A8, 18 Hoang Quoc Viet, Cau Giay, Hanoi, VIETNAM 2: Ecole Nationale Supérieur de Télécommunications de Brest 3: Université de Rennes 1 4: Centre d’Étude des Environnement Terrestre et Planétaire, CNRS de France

In frame of the scientific cooperation between the VAST and the CNRS, since 2005 three GSV4004 dual frequency GPS receivers are installed in Hanoi (21°02’50’’, 105o47'59"), in Hue (16°27’33’’,107°35’33’’) and in Ho Chi Minh city (10°50’54’’, 106°33’35’’) for monitoring the ionospheric scintillation and total electron content. These receivers and some ones in the Southeast asian region as Kunm in China, Ntus in Singapore and Bako in Indonesia which creates one chain of GPS receivers nearly along 105oE longitude to have ionospheric coverage from the 95°E to 120°E longitude and from 13°S to 30°N latitude. Using the pseudorange measurements recorded by these receivers, we compute the ionospheric total electron content (TEC) for each GPS station and establish the latitude, time and TEC maps. It shows that this GPS receiver chain is very good for the studies of TEC variation in the Equatorial ionization anomaly (EIA) in the Southeast Asian region. In this region where the magnetic equator is nearly parallel to the geographic one, latitude-time TEC map shows a geometry symmetrically with respect to the magnetic equator in the quite-time. It seems that it is not the case for the American region where the magnetic equator is not parallel to the geographic one. The TEC during some magnetic storms were computed from the data of these GPS receivers. It shows clearly that during the early stage of the magnetic storm, the EIA expanded poleward with large increases of the TEC, this provided evidence of a penetration magnetospheric eastward electric field and a strong plasma effect associated with the upward ExB plasma drifts. In the recovery phase, one



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to three days after the storm sudden commencement, the EIA is significantly reduced, the TEC value decreases and the crests move equatorward. These observations suggest that one to three days after the SSC onset, in the recovery phase, the ionospheric disturbance dynamo has an important influence on storm-time ionospheric electric fields at low latitudes, which significantly decreases the TEC value and affects the structure of the EIA. These observations are in agreement with the ones of some other authors. The comparisons between the vertical TEC derived from GPS data and the plasma frequency foF2 measured by ionosondes in Vietnam have been made. The influence of the atmosphere on the single-point positioning by GPS in Vietnam is also discussed.

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Study of the Total Electron Content (TEC) at an equatorial station

O. K. Obrou1, M. N. Mene1, A. T. Kobea1, K. Z. Zaka1, B. Ouattara1, and K. Groves2

1: Laboratoire de Physique de l'Atmosphère, Université de Cocody, 22 BP 582 Abidjan 22 2: Space Weather Center of Excellence , Air Force Research Laboratory, Hanscom AFB Massachusetts

The Total Electron Content (TEC) is of significant importance for the operation of ground and space based systems involving radio wave signal propagation. The equatorial ionosphere is subject to large spacio-temporal variations affecting accurate prediction of parameters such as TEC (Mendonca, 1960). The International Reference Ionosphere (IRI) is a widely used model to describe the electron density as well as TEC (Bilitza, 2001) of the ionosphere for a given location and time. Several authors (Adeniyi, 1997; Adeniyi and Radicella, 1998, Obrou et al., 2003, 2005) have studied the equatorial ionosphere with the IRI model and found larges discrepancies between the model results and the observed measurements. In this paper we compare the IRI predicted TEC with the GPS observed TEC recorded at the location of Abidjan (5.35°N, 3.98° W, dip -10.18°N) in Côte-d'Ivoire. The GPS data used are those of the Scintillation Network Decision Aid (SCINDA) deployed across the African continent. The result shows that the observed TEC overestimates the modeled TEC. However, the general trend is almost the same for both techniques apart from some fluctuation exhibit by the observed values.

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Inside LISN, an engineering perspective to its avant-garde conception

J. Valverde1, E. Silvestre1, and C. Valladares2

1: Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima, Perú ([email protected]) 2: Boston College, Boston, USA

The main goal of the project LISN is the construction of a network of ground-based sensors in South America to collect data from the equatorial ionosphere, working as a distributed observatory. On July 2008, an ensemble of 56 GPS receivers, 5 magnetometers and 5 ionosondes will provide data to a central server to be processed and distributed in real time. At the present, the network is constituted by 25 GPS stations and 2 magnetometer stations in test stage, all of them supervised by a continuous-monitoring system. This system has been developed to track the status of the network in real time, display it in the LISN web Page and send e-mail alerts. The resulting log files have provided a good means to determine the reliability of the network and the performance of the project in terms of data-hours per invested funds. An analysis of the most frequent causes of stations inactivity and their impact over the global capability of observation is presented. The result is a series of learned lessons about the construction, operation and upkeeping of a continental size multi-instrument, multi-institution real-time network.



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Some contributions of MAGDAS to the understanding of equatorial geomagnetic field behavior

A. B. Rabiu1, K. Yumoto2, I. A. Adimula3, J. O. Adeniyi3, and MAGDAS/CPMN Project group

1: Space Physics Lab., Dept. of Physics, Federal University of Tech., AKURE, Nigeria. ([email protected]) 2: Space Environment Research Centre, Kyushu University, Japan 3: Department of Physics, University of Ilorin, ILORIN, Nigeria

MAGDAS, Magnetic Data Acquisition System, is a growing network of more than 30 observatories. MAGDAS was successfully installed at the University of Ilorin, Nigeria – an equatorial station - in August 2006. MAGDAS is a strong component of International Heliophysical Year, IHY. This paper presented some of the contributions of MAGDAS to the understanding of equatorial geomagnetic field behavior. Diurnal and seasonal variations of the solar quiet daily variation in the three geomagnetic elements H, D, Z were studied. The EEJ indices were extracted for the 210 magnetic meridian and its spectral characteristics investigated. The obtained signatures of the magnetic field variations were discussed in light of literatures. This paper justified the need for a partner magnetic field observatory along same meridian as Ilorin, north or south of it, to facilitate synthesis of the equatorial electrojet effect.

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Africa and the International Heliophysical Year (IHY)

A. B. Rabiu1, B. J. Thompson2, C. Amory-Mazaudier3, M. C. Potgieter4, N. Seghouani5, D. Baylie6, O. K. Obrou7, M. C. Rabello Soares8, K. Yumoto9, K. Groves10, U. Inan11,

and D. Scherrer12

1: Department of Physics, Federal University of Technology, Akure, Nigeria. ([email protected]) 2: Laboratory for Solar & Space Physics, NASA Goddard Space Flight Center, Solar Physics Branch, Greenbelt, MD 20771, USA 3: CETP/CNRS, 4 Avenue de Neptune, 94107 Saint-Maur-des-Fossés, France 4: School of Physics, North West University. South Africa 5: Department of Astronomy & Astrophysics, Chemin de l’Observatoire, BP 63 Bouzareah, Algiers, Algeria 6: Department of Physics, Bahir Dar University, Bahir Dar, Ethiopia 7 : Laboratoire de Physique de l’Atmosphere, Universite de Cocody, Cote-D’ivoire 8: HEPL Solar Physics, Stanford University, 445 Via Palou, Stanford, CA 94305-4085, USA. 9: Space Environment Research Centre, Kyushu University, Japan 10: Space Weather Center of Excellence, Air Force Research Lab AFRL/VSBXI, Hanscom, USA 11: Space, Telecommunication, Atmosphere and Radio STAR laboratory, Department of Electrical Engineering, University of Stanford, USA. 12: Stanford Solar Center, Stanford University, USA

This paper assesses the participation of Africa in the ongoing International Heliophysical Year (IHY). IHY fosters ties between traditional/cosmic geophysics and astronomy. Astronomical Telescopes, Atmospheric Weather Electromagnetic System for Observation Modeling and Education AWESOME, Magnetic Data Acquisition System MAGDAS, Scintillation Network Decision Aid SCINDA, AMMA GPS and IGS GPS research facilities are the IHY intervention facilities already installed in African countries. The facilities are being well utilized and coordinated. National Organising Committees are being formed in individual member nations and the African Regional Committee is being strengthening towards the sensitization of the member countries and ultimate actualization of the goals of the



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International Cooperation program. Three continental IHY workshops have been held so far in Africa with participants drawn from several African states. The African IHY summer school has been scheduled for the last quarter of 2008. We describe the outreach activities across African axis during the 2006 total solar eclipse sponsored by IHY. Capacity building and technological transfer are part of the spin-off being derived from IHY. IHY is capable of providing a perfect bridge between north and south. African scientists and research institutes are already benefiting from the IHY planned international collaboration and cooperation. IHY is fostering strong intra–continental partnerships amongst African scientists.


Poster P4: Posters for Session S10 (Ionospheric storms and space weather effects)

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Irregularities at sub-auroral, middle, and low latitudes in the topside ionosphere observed during geomagnetic storms with the DEMETER and

DMSP satellites

R. Pfaff1, C. Liebrecht1, J.-J. Berthelier2, M. Parrot3, and J.-P. Lebreton4

1: NASA Goddard Space Flight Center, Greenbelt, MD, USA ([email protected]) 2: CETP, St. Maur, France 3: LPCE, Orleans, France 4: ESA, Noordwijk, Netherlands

Detailed observations of the plasma structure and irregularities that characterize the topside ionosphere at sub-auroral, middle, and low-latitudes are presented that were gathered with probes on the DEMETER and DMSP satellites during geomagnetic storms. Data from successive orbits reveal how the density structure and irregularities evolve with changes in the Dst. The observations reveal that precisely during the main phase of severe geomagnetic storms, increased ambient plasma densities and broad regions of irregularities are observed at 700 km, initially at storm commencement near the magnetic equator and then extending to mid- and sub-auroral latitudes within the ~8 hour period corresponding to the negative Dst excursions. Furthermore, intense, broadband electric and magnetic field irregularities are often observed at sub-auroral latitudes and are typically associated with the trough region and its poleward plasma density gradient. The observations provide a general framework showing how low, mid, and sub-auroral latitude plasma density structuring and associated irregularities respond to geomagnetic storms.

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Equatorial ionospheric disturbances during the October 29-31, 2003 storms

H. Kil and L. J. Paxton

Johns Hopkins University Applied Physics Laboratory ([email protected], [email protected])

We investigate the drivers of the ionospheric disturbances during the October 29-31 storms by analyzing the measurements of the ion density and velocity from the DMSP and ROCSAT-1 satellites, the optical observations from the TIMED/GUVI, and the GPS TEC. The observations of the plasma density at low latitudes during the storm show the significant enhancement and reduction of the plasma density in the American and Asian sector, respectively. The other fascinating feature is the occurrence of large equatorial plasma density depletions in the American-Atlantic sectors at night. The observed characteristics of the storm-time disturbances can be explained properly by considering the effect of the penetration electric field, thermospheric composition disturbance, and plasma instability. We will investigate the duration, local time and storm-phase dependence of the penetration electric field, the latitudinal and altitudinal extent of the composition disturbance, and the roles of the fountain effect and plasma instability for the formation of the large equatorial plasma depletions.



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Formation mechanism of quiet-time F2-layer disturbances at geomagnetic equator

A.V. Mikhailov, V.H. Depuev, and T.Yu. Leschinskaya

Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region 142190, Russia ([email protected])

The formation mechanism of ionospheric F2-layer disturbances at the geomagnetic equator not related to geomagnetic activity (Q-disturbances) was specified using model calculations. The Jicamarca ISR observations of ExB vertical drifts and DPS-4 digisonde data on NmF2 and hmF2 variations were used in model calculations for the periods of negative and positive Q-disturbances. The observed variations of ExB vertical drifts were shown to be the controlling parameter in the mechanism considered. Plasma recombination (its efficiency depends on geophysical conditions) in the lower F2-region is the integral part of the formation mechanism during nighttime hours. The F2-layer is shifted by downward drifts at the heights with different recombination efficiency. This explains the formation both positive and negative (with respect monthly median NmF2 values) Q-disturbances in the nighttime F2-region. Daytime positive Q-disturbances are due exclusively to a decrease in the vertical upward drift resulting in plasma accumulation in the F2-region. This type of disturbances can be related to a well-known counter electrojet effect which also takes place under geomagnetically quiet conditions. Rarely observed negative daytime Q-disturbances need for their explanation not only an increase of the upward plasma drift, but also a decrease in the thermospheric atomic oxygen abundance.

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Relative effects of electric field and neutral wind on positive ionospheric storms

N. Balan1, H. Alleyne1, Y. Otsuka2 and B. G. Fejer3

1: University of Sheffield, Sheffield S1 3JD, UK ([email protected]) 2: Nagoya University, Aichi 442-8507, Japan 3: Utah State University, Utah 84322-0500, USA

The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (Nmax) at low-mid latitudes in Japan longitudes (125E-145E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07-11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in Nmax around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind.



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E and F region midlatitude ionospheric drifts observed during geomagnetic storms.

J.Boska, D. Buresova D. Kouba, and P.Šauli.

Institute of Atmospheric Physics AS CR. Boční II/1401, 14131 Prague 4, Czech republic. boska@ ufa.cas.cz.

Digisonde drift measurements with DPS 4 equipment started at Průhonice observatory in January 2004. The paper deals with effects of high solar and geomagnetic activity, which were observed at Průhonice observatory in ionospheric drifts measurements during 2004 – 2007 year. Interesting changes of the ionospheric drifts were observed during several periods of a suddenly enhanced solar and geomagnetic activity.

In standard autodrifts measurements with DPS 4, the velocity of F region drifts is usually determined near peak of electron concentration profile.From 2005 we measure at Průhonice ionospheric drifts at the height interval 90 – 150 km also. In this paper we report the results of measurements of the drifts velocities in E and F regions during disturbed conditions at midlatitude station Pruhonice. Significant changes of the ionospheric drifts in both regions ( increasing of the vertical velocity, TID activity in horizontal components) were observed during several periods of a suddenly enhanced solar and geomagnetic activity in both ionospheric regions.

E region summer storm events - we observed strong increasing both horizontal components of the drift velocity, from typical value 10 -20 m/s till 50 m/s during medium events and 100m/s (during strong storm).The vertical component of the E region also increased, from quiet value 5m/s till 10- 15 m/s during medium events and 20 m/s during strong event.

E region winter storms -more dramatic increasing of all drift velocities components was observed (50 – 100 m/s vertical drift component). Significant height changes of the drift velocity height profile in the interval of heights 90 – 130 km during winter event was observed.All components of the ionospheric F region drift velocity, measured during medium and strong geomagnetic events are strongly disturbed by storm conditions. Observed drift velocity components reached during strong storm values ~100- 150 m/s during summer and ~500 m/s during winter storms. Highest increasing F region drift velocity was observed during winter ionospheric storm 14 – 16. 12. 2006.

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Night-time Sudden Commencements observed with CHAMP and Ground-based Magnetometers

K. Schlegel1, H. Lühr2, M. Rother2, and K. Yumoto3

1: Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany ([email protected]) 2: Geoforschungszentrum, Potsdam, Germany 3: Kyushu-University, Fukuoka, Japan

According to current understanding Sudden Commencements (SC) in magnetometer records are caused by a sudden compression of the magnetosphere by shocks (dynamic pressure steps) in the solar wind. So far SCs have mainly be studied with the help of magnetometer arrays, only very few systematic studies with satellite borne magnetometers have been published. We present a systematic study of 30 SCs observed by CHAMP on the night side (between 18 and 06 MLT) at low and mid-latitudes (between -45° and +45° MLat) between July 2000 and December 2006. CHAMP is a polar orbiting satellite (87.25° inclin.)



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cruising at altitudes between 360 and 430 km. The SCs are recorded with the onboard fluxgate magnetometer and identified after subtracting the main magnetic field. For comparison, ground-based magnetometer records with 1-s time resolution from stations close to the satellite track have been used.

During night-time, effects of ionospheric currents on the magnetic field are believed to be negligible, thus the SC magnetic signature represents only the effect of magnetospheric compression. The shape of the magnetic field step should therefore look very similar at satellite altitudes and on the ground. We demonstrate this with three (out of our 30 analysed) events observed at different geographical locations. Moreover, the magnitude of the magnetic field step is clearly related to the step size in the solar wind dynamic pressure.

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Study of ionopsheric scintillation using GPS signals measured at Ascension Island

M.M.J.L. van de Kamp1 and P. S. Cannon1,2

1: Dept. of Elec. and Elec. Eng, University of Bath, Bath, United Kingdom 2: Centre for RF Propagation and Atmospheric Research, QinetiQ, Malvern, United Kingdom

High cadence GPS signals have been collected on Ascension Island, in the South Atlantic, during sunspot minimum, and in Vanimo, Papua New Guinea, during sunspot maximum. Both locations lie in the equatorial crest region. Data were collected at sampling frequencies of 1 Hz at Ascension, and 0.5 Hz at Vanimo. Vertical TEC (Total Electron Content) was calculated from the differential phase of the signals received at the two GPS frequencies.

The TEC data are analysed for the properties of their spatial fluctuation spectrum. A parameter indicating the scintillation spectral strength, equivalent to the parameter CkL used in

scintillation prediction models such as WBMOD, is derived from this spectral analysis. The relation between this parameter and the more commonly used parameter S4 is analysed.

Also, the spectral slope of TEC is derived from the spatial spectrum for scale sizes smaller than 2 km (and larger than the inverse of the highest measured frequency, which is around 100 m).

The resulting spectral slope is often significantly affected by system effects such as receiver noise and phase discontinuities. This causes an apparent dependence of the slope on fluctuation strength.

The spectral slope is analysed in terms of other parameters for a subset of data for which the results should not be affected by mentioned systems effects. From this analysis, it is observed that the spectral slope is dependent on the hour of the day, both for Ascension and Vanimo. This is in agreement with results from other researchers.

The spectral slope is significantly higher in Vanimo than in Ascension. This difference could be either due to the geographical difference, or to the different measurement period (high/low sunspot number).

Using a theoretical analysis, it is shown that the value of the spectral slope, and therefore its variation, affects the abovementioned relation between scintillation spectral strength and S4. The observed variation of the spectral slope of scintillation is therefore important to be noted.



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Response of equatorial and low latitude ionosphere in Indian region during some severe geomagnetic storms: A study

S. Sripathi1, S. Bose1, D. Tiwari1, S. Banola1, B. Kakad1, A. Bhattacharyya1 and T. K. Pant2

1. Indian Institute of Geomagnetism, Navi Mumbai, India ([email protected]) 2. Space Physical Laboratory, Trivandrum, India

In this paper, the influence of some of the intense geomagnetic storms (namely 11-12 April, 2001, 20-21 November, 2003, 7-10 November, 2004, 24-25 August, 2005 and 15-16 May, 2005) on equatorial and low latitude ionosphere is investigated in the Indian longitude zone using (1) Total Electron Content (TEC) measurements obtained from Global Positioning System (GPS) receivers, which is provided by SAC under the GAGAN project (2) Ionosonde data from Trivandrum, an equatorial station (dip latitude 0.6ºN) and (3) Amplitude scintillation observations on a 251MHz signal transmitted from a geostationary satellite and recorded at Mumbai (dip latitude 13.5oN). The observations are broadly classified into three categories. While in the first case, the Bz value was nearly –50nT, with

hrnTtBz /50/ >∂∂ and it remained southward for more than 3 hrs and in the second case Bz was

nearly –50nT with hrnTtBz /10/ >∂∂ and it remained southward for longer duration (>15 hrs). In the

third case, sudden decrease of AL index associated with prompt penetration of electric field to the equatorial and low latitude region. In the first case, the enhancement in TEC is observed nearly two hours after Bz turned southward. In this case, the enhancement in TEC over equatorial ionization anomaly (EIA) region was found to be as high as 30 TEC units. Interestingly, in one of the cases i.e., 24 August 2005 we found very weak daytime anomaly but the anomaly was developed later around post sunset hours (17-19 LT). Further, the anomaly in the evening showed two peaks two hours apart. FoF2 obtained at Tirunelveli also shows a similar oscillatory behavior. While increase in TEC and latitudinal extent associated with the EIA can be understood to be due to changes in the vertical plasma drift due to the presence of zonal electric field as well as equatorward meridional neutral wind, observation of two anomaly peaks is new. This splitting of anomaly could be attributed to the storm time changes in the zonal winds. In the second case, significant TEC enhancement is seen 20-30 hrs after Bz turned southward. This could be attributed to the effect of disturbance dynamo. In the last case, strong VHF scintillations are observed at Mumbai on 11 April 2001 around 06LT, which was associated with large increase in h’F at equatorial station Trivandrum. This could be due to the penetration of storm time electric field change. Satellite observations like ROCSAT, DMSP and TIMED GUVI have also been used in addition to the ground based datasets to study the signatures of these severe geomagnetic storms over the Indian region.


Session 11: Where are we going? Outstanding questions, future trends and challenges

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Atmospheric wave dynamics and their effects on the equatorial ionosphere: What do we know, what are the unknowns, and which are the important

topics?

D. C. Fritts

NWRA/Colorado Research Associates, Boulder, CO ([email protected])

This talk will briefly review some of what we understand of neutral atmosphere wave influences in the ionosphere. The major emphasis, however, will be on where our understanding of these coupling processes is poor or absent, and which areas might be most important in advancing our knowledge of their ionospheric effects. We are developing a better understanding of the penetration of small- and large-scale waves into the thermosphere and ionosphere, and of their potential in situ sources at higher altitudes. Nevertheless, there remain significant uncertainties in how (and in some cases whether) these motions contribute to plasma processes in the ionosphere. Specific topics include 1) the amplitudes and scales of waves able to reach very high altitudes, 2) the impacts of momentum transport and mean forcing accompanying such motions, 3) the role of neutral instability dynamics in the thermosphere, and 4) potential seeding of plasma instabilities, especially ESF and RTI triggering plasma bubbles extending to much higher altitudes.

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Meteor science and layering phenomena in the lower thermosphere. Is there anything that we lack in basic knowledge

and how should we go about getting it?

J. D. Mathews

The Pennsylvania State University, University Park, PA, USA ([email protected])

The micrometeoroid mass flux into the upper atmosphere has long been recognized as providing the atomic metal ions necessary to the formation of sporadic-E and lidar-visible metal layers. While this mass flux as a function of local time, season, and latitude remains very much an issue, recent VHF and UHF HPLA (High-Power, Large Aperture) radar meteor head-echo observations have provided estimates of this flux using direct radial or 3-D Doppler and deceleration measurements that yield good particle mass estimates under reasonable assumptions. These observations have shown that the micrometeoroid speed distribution is much higher than previously assumed and that the well know visible meteor showers contribute little mass to the upper atmosphere relative to the daily sporadic meteoroid flux. Other issues now being addressed with HPLA radars include details of the meteoroid interaction with atmosphere and the related radio science and plasma physics issues that must be resolved in order to understand what the radar actually “sees”. In particular, we now recognize that the meteoroid interaction with the atmosphere is anything but simple with meteoroids undergoing fragmentation and terminal (explosive) events thus complicating observations and pointing to a significant mass flux component in nanometer particle form rather than atom-level ablation products. Observations of long-lived range-spread (meteor) trail-echoes (RSTEs) have led to the understanding that these events are caused by the rapid alignment of the meteor trails along the geomagnetic field yielding FAI-scattering. RSTE observations then enable the study of the plasma processes including diffusion and electrodynamic instabilities that drive the trail-plasma to B-field align. These studies also cast new light on the diffusion rates determined using “classical” meteor radar



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observations of decaying trail-echoes and on the formation of altitude-narrow ion layers. We note that multi-frequency, common-volume radar meteor observations will prove especially useful in resolving the issues raised.

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What else can we learn with coherent scatter radars about E and F region irregularities that we don’t know? What else can we learn about ESF and

midlatitude SF?

J. L. Chau et al.

Radio Observatorio Jicamarca, Instituto Geofísico del Perú, Lima ([email protected])

Coherent scatter radars have been used since the early 1950s to study the ionospheric E and F region irregularities at all latitudes. Since then, and in particular in last decade, such systems have proliferated around the world with varying degrees of sophistication, complexities and usage, most of them operating in the HF and VHF frequencies. Observations from these systems are currently being used to study the plasma processes behind the echoes, to diagnose the ionosphere region they are embedded in and therefore study the ionosphere electrodynamics, to characterize and forecast (?) the occurrence of scintillation activity, to complement and validate measurements done with other instruments, etc. In this presentation we present a brief overview of how current coherent radars are being used, making emphasis on their main focus and current limitations. Then, as the title and session description indicates, we will present our view of what are the current outstanding questions, how coherent radars will be and should be used in the future depending on the different research and/or operational objectives.

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What are the objective/needs for new theoretical work on E and F region plasma instabilities and electrodynamics?

J.-P St.-Maurice

University of Saskatchewan, Canada ([email protected])

The first goal of plasma instability theories is answer the very basic question: “What are the instability mechanisms responsible for the production of the irregularities that we observe?” At first sight, the generic answer is deceptively simple and based on the various ways by which the plasma can be made to depart from equilibrium: in this regard, currents and density gradients have been the foundations for many successful theoretical explanations of observed ionospheric irregularities. Theorists have also rightly pointed out that thermal gradients, shears, and even non-Maxwellian ion velocity distributions can all destabilize the plasma. Studies combining several of these processes have also been published. In spite of this, however, we are faced with a general lack of endorsement for these processes. Ironically, in spite of all these general theoretical studies and in spite of many ingenious proposals for instabilities, some irregularities, like the so-called low latitude “150 km echoes”, are basically not understood. This leads me to the thought that the first challenge for theorists is to make their theories “more relevant”. When exploring new mechanisms, we should look much more closely at all possible constraints from the observations so as to make convincing cases for particular mechanisms. Theorists should also have some brainstorm sessions together and with experimentalists to solve riddles like the 150 km echoes. It’s all about relevance.



194

The second challenge is not new but remains important and needs to be pursued as vigorously as ever. I refer of course to the need to understand the nonlinear evolution of instabilities, particularly in situations for which we know the linear excitation mechanism. This need is once again triggered by the observations, which are strongly biased to large amplitude structures and therefore often require nonlinear theories. The nonlinear work is important because it is linked to a fundamental practical application of irregularity studies, namely, their capability to tell us something about the medium (for instance about the plasma drift). The nonlinear problem goes well beyond the linear one, which simply tries to figure out the basic feedback mechanisms that lead to instability. It addresses the actual properties of the structures once nonlinear processes associated with large amplitudes have contributed to the evolution of the system. For instance, the Doppler shift of E region irregularities is still a subject of debate. In this instance I also would suggest that we have another look at observations and consider the possibility that we no longer just see only structures that have reached their saturation amplitude when we do sophisticated interferometry based observations. The smaller amplitude echoes may well have properties that differ by being more “linear-like”. Another application of nonlinear studies pertains to the general shape of F region spectra: we now have convincing evidence that the spectral width at HF frequencies has a distinct morphological signature associated with magnetospheric boundaries. Indeed it is sometimes forgotten that the spectral shape offers some very important clues: a very narrow spectrum has to be associated with weak turbulence, that is, with a slowly growing condition. We should not use power to determine the degree of turbulence, but rather we should use the spectral width. Therefore, when we look for theoretical descriptions, we should perhaps pay attention to the fact that in some cases we have strong turbulence (wide spectra), and in other cases we have weak turbulence. In the latter instance, we might want to consider whether or not a nonlinear theory is really needed. At the very least, weak turbulence should suffice. Be that as it may, we have another challeng to face: nonlinear systems offer yet another challenge in that they can trigger new instabilities nonlinearly. Neat examples of this are the trigger of m-size irregularities in the equatorial electrojet through much larger scale gradient-drift structures. At high latitudes we also have the example of Langmuir turbulence having been proposed as a trigger mechanism for large amplitude ion-acoustic waves. And finally, we must include non-local effects in the nonlinear category. What do people make for instance, of the fact that an “eigenfrequency” would in principle be a function of space? There are ways around that contradiction but they all involve nonlinear work of one form or another.

A third challenge is to figure out the role that the irregularities play in the system. In the long run, this has to be the most important challenge. But, it’s also the most difficult. With this challenge we address the fundamental issue of the plasma instabilities: if they are created by a lack of equilibrium, this also means that their role is to bring the plasma closer to its equilibrium, somehow. If currents are the trigger, then they should somehow weaken. Likewise if density gradients or shears are the trigger, they should be weakened by the instability. This brings us to the calculation of anomalous transport coefficients, which, to my taste, is still often an art more than a science. That’s partly because we have too few constraints to go by. However, every once in a while the plasma gives us useful clues that we can work with. For instance, the current profile in the equatorial electrojet gives us clues about the anomalous resistivity, while the electron heating in the high latitude electrojet gives us a wave heating rate and tells us about the importance of parallel electric fields in the nonlinear evolution of the structures (interestingly enough, in a modified two-stream instability, one way to stabilize the plasma is indeed to heat the electrons). The third challenge, in other words, is to quantify the anomalous transport coefficients that would allow us to properly adjust the global properties of the plasma through proper effective transport coefficients. This is not easy: sometimes we cannot even seem to agree on the processes that control the nonlinear evolution, as exemplified by the debate that took place regarding electron heating at high



195

latitudes, with one school of thought pushing for anomalous diffusion while another favoured parallel wave electric fields.

________________________________

Optical investigation of the ionospheric and atmospheric dynamics. How can we learn something more that is significant?

K. Shiokawa

Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan ([email protected])

The development of highly-sensitive cooled-CCD cameras makes it possible to obtain two-dimensional images of waves and disturbances in the thermosphere and the mesopause region. The quantum efficiency of a thinned and back-illuminated cooled-CCD camera is very high (more than 90 percent in visible wavelengths) compared with that of less than 20 percent for previously-used image intensifiers and multi-channel plates. Applications of these cooled-CCD cameras to rotational temperature photometers and Fabry-Perot interferometers also give useful information regarding the temperatures and wind vectors in the upper atmosphere. In this invited talk, we review optical observations of the mesosphere and the thermosphere using cooled-CCD cameras through nocturnal airglow emissions, and discuss their possibility to solve various questions on the dynamics of the mesosphere, thermosphere, and ionosphere.

________________________________

Accuracy issues of the existing thermospheric wind models. Can we rely on them in seeking solutions to wind driven problems?

M. F. Larsen1

1: Clemson University, Clemson, South Carolina, USA ([email protected])

The neutral winds are a critical driver for the electrodynamics, as well as many plasma processes, at mid and low latitudes. Obtaining better and more extensive measurements of the neutral circulation in the ionosphere has been an ongoing objective since the earliest days of ionospheric studies. The available measurement techniques generally cover limited altitude ranges and limited horizontal regions. The data coverage in the E region is especially sparse. The available data limit the development of empirical models, which, in any case, provide representations of average conditions rather than the extremes. The sparse data coverage also limits the initialization and verification of the physics-based models. The available models for characterizing the E- and F-region neutral winds, including the empirical and physics-based numerical models, will be summarized briefly. The extent to which each type of model can be expected to provide realistic drivers for E- and F-region electrodynamics will be discussed. Finally, a set of goals for improving the representation of the winds will be presented.


List of Participants

197

LIST OF PARTICIPANTS Abdu Mangalathayil Ali Brazil [email protected] Adachi Toru Japan [email protected] Alken Patrick USA [email protected] Ambrosiadi Nino Greece [email protected] Anderson David USA [email protected] Anderson Phillip USA [email protected] Arras Christina Germany [email protected] Astafyeva Elvira Japan [email protected] Balan Nanan UK [email protected] Bankov Ludmil Bulgaria [email protected] Bass Elisabeth USA [email protected] Bernhardt Paul USA [email protected] Bhattacharyya Archana India [email protected] Bhoo Pathy Nyanasegari Malaysia [email protected] Biktash Lilia Russia [email protected] Bishop Rebecca USA [email protected] Bösinger Tilmann Finland [email protected] Borries Claudia Germany [email protected] Boska Josef Czech Republic [email protected] Bourdillon Alain France [email protected] Buresova Dalia Czech Republic [email protected] Buriti Costa Ricardo Arlen Brazil [email protected] Burke William USA [email protected] Cahoy Kerri USA [email protected] Carlson Herb USA [email protected] Chau Jorge Peru [email protected] Christakis Nikos Greece [email protected] Clemesha Barclay Brazil [email protected] Clemmons James USA [email protected] Coker Clayton USA [email protected] Comberiate Joseph USA [email protected] Cosgrove Russel USA [email protected] Das Uma India [email protected] De la Beaujardieire Odile USA [email protected].

mil De Meneses Francisco Brazil [email protected] De Nardini Clezio Brazil [email protected] Depuev Victor Russia [email protected] Devi Minakshi India [email protected] Dimant Yakov USA [email protected] Duryd Lars USA [email protected] Earle Gregory USA [email protected] Fang Tzu-Wei Taiwan [email protected] Farley Donald USA [email protected] Fejer Bela USA [email protected] Fesen Cassandra USA [email protected] Foster John USA [email protected] Fritts David USA [email protected] Fukao Shoichiro Japan [email protected]



198

Gadimova Sharafat Austria [email protected] Galindo Freddy Peru [email protected] Gelinas Lynette USA [email protected] Goi Yukari Japan [email protected]. Grieger Norbert Germany [email protected] Guo Liyu USA [email protected] Gupta Surya India [email protected] Haeusler Kathrin Germany [email protected] Haldoupis Christos Greece [email protected] Haralambous Harris Cyprus [email protected] Hasbi Alina, Marie Malaysia [email protected] Haubolt Hans Austria [email protected] Hawlitschka Stefan Germany [email protected] Hedden Russel USA [email protected] Heelis Rod USA [email protected] Hoeg Per Denmark [email protected] Huba Joe USA [email protected] Hurd Lucas USA [email protected] Hussey Glenn Canada [email protected] Hysell David USA [email protected] Ilma Ronald USA [email protected] Inan Umran USA [email protected] Ishii Mamoru Japan [email protected] Kagan Ludmila Canada [email protected] Kalogerakis Konstantinos USA [email protected] Karpachev Alexander Russia [email protected] Kato Susumu Japan [email protected] Kaufmann Martin Germany [email protected] Kawatani Yoshio Japan [email protected] Kelley Michael USA [email protected] Kherani Alam Brazil [email protected] Kikuchi Takashi Japan [email protected] Kil Hyosub USA [email protected] Klenzing Jeffrey USA [email protected] Klimenko Maxim Russia [email protected] Kofman Wlodek France [email protected] Kouba Don Czech Republic [email protected] Krall Jonathan USA [email protected] Kudeki Erhan USA [email protected] Larsen Miguel USA [email protected] Lastovicka Jan Czech Republic [email protected] Le Hui Minh Vietnam [email protected] Lehmacher Gerald USA [email protected] Lieberman Ruth USA [email protected] Lin Chien Hung Taiwan [email protected] Liu Libo China [email protected] Liu Han-Li USA [email protected] Lomidze Levan Georgia [email protected] Lühr Hermann Germany hLü[email protected] Makela Jonathan USA [email protected] Malhotra Akshay USA [email protected] Mantas George Greece [email protected] Martinis Carlos USA [email protected]



199

Maruyama Takashi Japan [email protected] Maruyama Naomi USA [email protected] Mascarenhas Matheus Brazil [email protected] Mathews John USA [email protected] Meriwether John USA [email protected] Mikhaylov Andrey Russia [email protected] Milla Marco USA [email protected] Miller Kent USA [email protected] Miller Ethan USA [email protected] Muralikrishna Polinaya Brazil [email protected] Murr David USA [email protected] Nakata Hiroyuki Japan [email protected] Neubert Torsten Denmark [email protected] Nishioka Michi Japan [email protected] Novotna Dagmar Czech Republic [email protected] Oberheide Jens Germany [email protected] Obrou Olivier Ivory Coast [email protected] Ogawa Tadahiko Japan [email protected] Oppenheim Meers USA [email protected] Otsuka Yuichi Japan [email protected] Pacheco Edgardo USA [email protected].

edu Pancheva Dora Bulgaria [email protected] Pfaff Robert USA [email protected] Pi Xiaoqing USA [email protected] Pimenta Alexandre

Alvares Brazil [email protected]

Pinedo Nava Henry Peru [email protected] Radicella Sandro Italy [email protected] Rao N. Venkateswara India [email protected] Reid Iain Australia [email protected] Reyes Pablo USA [email protected] Rowland Douglas USA [email protected] Saito Akinori Japan [email protected] Scherliess Ludger USA [email protected] Shalimov Sergey Russia [email protected] Shiokawa Kazuo Japan [email protected] Sidorova Larissa Russia [email protected] Silvestre Espinoza Elisabeth Peru [email protected] Simonich Dale Brazil [email protected] Sindelarova Teresa Czech Republic [email protected] Singer Werner Germany [email protected] Sripathi Samireddipalle India [email protected] St-Maurice Jean-Pierre Canada [email protected] Stolle Claudia Germany [email protected] Sugar Glenn USA [email protected] Swartz Wesley USA [email protected] Swenson Gary USA [email protected] Takahashi Hisao Brazil [email protected] Taylor Mike USA [email protected] Tiwari Diwakar India [email protected] Tsagouri Ioanna Greece [email protected] Tsugawa Takuya Japan [email protected]



200

Tsunoda Roland USA [email protected] Uemoto Jyunpei Japan [email protected] Urbina Julio USA [email protected] Vadas Sharon USA [email protected] Valladares Cesar USA [email protected] Van de Kamp Max UK [email protected] Vasyliunas Vytenis Germany [email protected] Vincent Robert Austrralia [email protected] Wan Weixing China [email protected] Ward William Canada [email protected] Watanabe Shigeto Japan [email protected] Whalen James USA [email protected] Woodman Ronald Peru [email protected] Xiong Jiangang China [email protected] Yamamoto Masayuki Japan yamamoto.masa-yuki@kochi-

tech.ac.jp Yamamoto Mamoru Japan [email protected] Yee Sam USA [email protected] Yokoyama Tatsuhiro USA [email protected] York George USA [email protected]


First/Presenting Author Index

201

Name Program

Page Abstract

Page Abdu 19 83Adachi 28 136Adeniyi / Radicella 16 64Alken 27 124Ambrosiadi 30 150Anderson D. 27 124Anderson P. C. 21 92Arras 22 100Arras 28 132Astafyeva 30 149Astafyeva 32 165Aveiro / Denardini 16 64Ayoola 16 64Balan 26 122Balan 35 188Bankov 30 149Bass 19 81Belyey / Chau 21 93Bernhardt 29 143Bernhardt 34 175Bhattacharyya 21 91Biktash 23 105Biktash 32 166Bishop 28 131Borries 33 171Bösinger 27 127Boska 35 189Bourdillon 19 77Buresova 33 168Buriti Costa 16 65Burke 32 167Cahoy 13 50Candido / Pimenta 23 106Chanrion / Neubert

28 137

Chau 21 93Chau 37 193Choudhary / J.-P. St.-Maurice

18 74

Christakis 30 145Clemesha 14 54Clemmons 15 63Clemmons 34 175Coker 31 153Comberiate 31 154Cosgrove 28 132Das 14 57

De Meneses 22 105Denardini 18 76Denardini 21 95Depueva / Mikhaylov

33 170

Devi 16 65Devi 30 152Dimant 22 103Duryd 19 80Earle 14 52Earle 31 153England 23 106Fang 27 125Farley 11 41Fejer 20 84Fesen 27 129Foster 32 164Fritts 28 131Fritts 37 192Fukao 20 87Gadimova 32 164Galindo 34 178Gelinas 14 55Gerrard 34 178Goi 32 167Grieger 15 59Guo 15 61Gupta 19 81Gupta 22 98Häeusler 13 51Haldoupis 15 62Haralambous 34 179Haralambous 34 180Hasbi 33 168Häusler 13 51Hawlitschka 34 179Hedden 27 128Heelis 12 43Høeg 13 46Høeg 35 182Huba 23 107Huba 26 119Hurd 11 57Hussey 22 97Hysell 18 70Hysell 31 158Ilma 18 75Immel / England 31 155Inan 12 44

FIRST/PRESENTING AUTHOR INDEX



202

Ishii 23 107Kagan 18 71Kagan 21 94Kalogerakis 31 154Karpachev 23 108Karpachev 33 171Kato 13 46Kaufmann 14 56Kelley 12 43Kelley 27 123Kelley 33 169Kherani 21 92Kherani 21 94Kherani 30 151Kikuchi 20 90Kil 27 126Kil 35 187Klenzing 31 155Klimenko 26 121Klimenko 29 138Klimenko 29 138Kofman 11 Kouba 22 101Kouba 34 177Kovalev / Dimant 18 73Krall 20 85Kudeki 19 83Kumar G. K. / Patra

16 66

Larsen 13 49Larsen 21 97Larsen 37 195Lastovicka 29 137Le Hui 35 183Lehmacher 14 52Lieberman 13 48Lieberman 15 60Lima / Takahashi 16 69Lin 26 119Lin 34 177Liu H.-L. 14 54Liu L 23 108Lomidze 22 100Lu / Swartz 18 76Lühr 27 128Lühr 29 141Makela 32 161Malhorta 19 80Malhotra 22 102Manoj / Lühr 33 169Martinis 23 109Martinis 28 135Maruyama N. 23 109

Maruyama N. 26 120Maruyama T. 15 62Mascarenhas 23 110Mathews 28 133Mathews 37 192Medeiros / Taylor 13 49Mendillo 23 110Mendillo 26 119Meriwether 13 48Meriwether 27 128Mikhaylov 35 188Milla 31 157Miller 21 90Muralikrishna 18 75Muralikrishna 34 176Nakata 23 111Namgaladze / Klimenko

29 139

Nishioka 23 111Oberheide 15 58Obrou 35 184Ogawa 20 89Ogawa 30 144Oladipo / Radicella

34 181

Oppenheim 18 73Orue / Radicella 32 166Otsuka 20 85Pacheco 30 148Pancheva 15 60Park / Lühr 23 112Patra 19 78Patra 29 142Pfaff 20 86Pfaff 22 96Pfaff 28 134Pfaff 34 174Pfaff 35 187Phanikumar / Patra

22 102

Pi 26 123Pimenta 24 113Pinedo Nava 24 113Rabiu 29 140Rabiu 35 185Rabiu 35 185Rabiu / Fayose 35 182Radicella 34 180Ramkumar 28 130Rao N. V. 19 77Rao N.V. 21 98Reyes 31 158Rowland 14 53



203

Saito 30 144Saito 31 156Saito 34 178Sato / Kawatani 13 45Scherliess 33 172Schlegel / Lühr 35 189Seiradakis 17 70Shalimov 22 99Shalimov 30 144Shiokawa 37 195Sidorova 20 86Sidorova 24 114Siefring / Bernhardt

32 160

Silvestre 35 181Simonich 13 50Sindelarova 30 145Singer 15 61Sinha / Das 16 67Sripathi 20 88Sripathi 24 115Sripathi 30 147Sripathi 35 191St-Maurice 18 72St-Maurice 37 193Stolle 20 84Sugar 22 103Swartz 29 142Swenson 28 135Swenson 32 162Takahashi 20 89Talaat / Yee 30 147Taylor 14 56Tiwari 24 115Tsagouri 33 172Tsugawa 33 170Tsunoda 19 77Tsunoda 19 78Tsunoda 20 83Uemoto 26 121Urbina 28 134Vadas 14 55Vadas 28 131Vadas 24 116Valladares 31 156Valverde / Silvestre

35 184

Van de Kamp 36 190Vasyliunas 26 118Vincent 11 42Wan 27 125Ward 15 58Watanabe 30 146

Whalen 21 91Whalen 24 116Woodman 11 41Wrasse / Takahashi

16 67

Wrasse / Takahashi

16 68

Xiong 30 148Yamamoto M. 13 47Yamamoto M. 34 174Yamamoto M.-Y. 32 162Yokoyama 29 141Yokoyama 32 159Younger / Reid 28 133


205

Ithaca

When you set out on your journey to Ithaca, pray that the road is long, full of adventure, full of knowledge. The Lestrygonians and the Cyclops, the angry Poseidon -- do not fear them: You will never find such as these on your path, if your thoughts remain lofty, if a fine emotion touches your spirit and your body. The Lestrygonians and the Cyclops, the fierce Poseidon you will never encounter, if you do not carry them within your soul, if your soul does not set them up before you. Pray that the road is long. That the summer mornings are many, when, with such pleasure, with such joy you will enter ports seen for the first time; stop at Phoenician markets, and purchase fine merchandise, mother-of-pearl and coral, amber and ebony, and sensual perfumes of all kinds, as many sensual perfumes as you can; visit many Egyptian cities, to learn and learn from scholars. Always keep Ithaca in your mind. To arrive there is your ultimate goal. But do not hurry the voyage at all. It is better to let it last for many years; and to anchor at the island when you are old, rich with all you have gained on the way, not expecting that Ithaca will offer you riches. Ithaca has given you the beautiful voyage. Without her you would have never set out on the road. She has nothing more to give you. And if you find her poor, Ithaca has not deceived you. Wise as you have become, with so much experience, you must already have understood what Ithacas mean.

K. P. Kavafis, 1911

12th International Symposium12th International Symposium

on Equatorial Aeronomy

SPONSORS

National Science Foundation - Division of Atmospheric SciencesEuropean Office of Aerospace Research and DevelopmentEuropean Office of Aerospace Research and DevelopmentThe Aerospace CorporationCommittee on Space ResearchScientific Committee on Solar Terrestrial PhysicsInternational Union of Geodesy and GeophysicsInternational Union of Geomagnetism and AeronomyInternational Union of Geomagnetism and AeronomyInternational Union of Radio ScienceInternational Committee on Global Navigation Satellite SystemsGreek Ministry of National Education Physics Department, University of CreteJohn S Latsis Public Benefit FoundationJohn S. Latsis, Public Benefit FoundationAgricultural Bank of GreeceHellenic Telecommunications OrganizationLARCO General Mining and Metallurgical Company

Hosted by:The Department of PhysicsUniversity of Crete Heraklion, Crete, Greece

http://isea12 physics uoc grhttp://isea12.physics.uoc.gr

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