Исследование турбулентности магнитосферно-ионосферной плазмы в

высокоширотной области

И.В.Головчанская, Б.В.Козелов

Observations

• Dynamics Explorer 2 (DE2), altitudes 300-900 km, 1.5 year mission. • Database:• dc electric field (VEFI, double sounding technique), sensitivity 0.1 mV/m

magnetometer data (IGRF subtracted), sensitivity 1.5 nT • Resolution:16 Hz (~500 m).• Optics:• Auroral Large Imaging System (ALIS) • Field of view ±17° from magnetic zenith, • Dynamical range 2·104 • Electrodynamics:• Signal-to-noise ratio 102-103

• One-pixel resolution ~ 400 m• Substorm conditions• OMNI database• Hourly IMF and solar wind parameters

Representative events

Golovchanskaya I. V., Y. P. Maltsev, A. A. Ostapenko, High-latitude irregularities of the magnetospheric electric field and their relation to solar wind and geomagnetic conditions , J. Geophys. Res., 107, NA1, doi:10.1029/2001JA900092, 2002.

)2

)/(lnexp()2

exp(2

1)( 20

2

02

2

2

xdx

Castaing distribution:

where λ characterizes the degree of non-Gaussianity of data and lnα0 = - λ2 .

IMF By = -17.9 nT,IMF Bz = 13.4 nT

Discrimination between fluctuations on the closed and open magnetic field lines.

Kozelov B. V., I. V. Golovchanskaya, A. A. Ostapenko, and Y. V. Fedorenko, Wavelet analysis of high-latitude electric and magnetic fluctuations observed by the Dynamic Explorer 2 satellite, J. Geophys. Res., 113, A03308, doi:10.1029/2007JA012575, 2008.

IMF By = -15.1 nT,

IMF Bz = -6.7 nT

Precipitation data: LAPI on DE2.

Auroral zone

Polar cap

Turbulence occurrence regions. Relation to the IMF and large-scale Birkeland currents. Electric fields (VEFI on DE2)

)(1

0 yB

xB

j xyz

, where < > means ILAT-MLT bin averaged for ~5000 DE2 passes for 1.5 year.

Golovchanskaya I. V., A. A. Ostapenko, B. V. Kozelov, Relationship between the high-latitude electric and magneticturbulence and the Birkeland field-aligned currents, J. Geophys. Res., 111, A12301, doi:10.1029/2006JA011835, 2006.

Magnetic fields (magnetometer on DE2)

Electric field spectra and their interpretationKintner and Seyler [1985]

Data: ac electric field spectrometeron Hawkeye 1,2 Hz < f < 56 HzBalloon measurements,Altitudes 30 –40 kmf < 0.03 Hz

Doppler shifted frequencies:2f = Vsat·k

Interpretation:Kraichnan regime of electrostatic(fluid type) ionosphericturbulence (?).

Prediction: change of the slopeat 1–10 km.

Investigation of electric field spectrum slopes on larger statistics [Heppner et al., 1993] Data: ac electric field spectrometer on DE2, 4 Hz < f < 512 Hz

Findings: (1) Peculiarity around local O+ gyrofrequency (32 – 64 Hz); (2) Seasonal variation of spectrum slopes;

Turbulence source localization

E

E

P

j B

o

EP

jB

Ionospheric source Magnetospheric source

Gurnett et al., 1985 (DE1,altitude 3–4 Re),Podgorny et al., 1988, 2003 (Bulgaria-1300 ,altitude 900 km)found predominantly downward direction of the associated Poynting flux,implying a magnetospheric source of the turbulence.

Golovchanskaya I. V. and Y. P. Maltsev, On the direction of the Poynting flux related to the mesoscale electromagnetic turbulence at high latitudes, J. Geophys. Res., 109, A10203, doi:10.1029/2004JA010432, 2004 (DE2).

DE2, 1981 day 304 DE2, 1981 day 290

-120

-80

-40

0

40

80

Ex,

mV

/m

U TINV .LAT

M LT

81.5 79.17.7 7.3 23.0 20.2

63.5 54.42342 2348 2354 2400

2342 2348 2354-250

-200

-150

-100

-50

0

50

By,

nT

2400

2342 2348 2354-2000

0

2000

4000

6000

8000

P,W

/km

2

2400

-120

-80

-40

0

40

80

120

Ex,

mV

/m

77 .1

23.980.9

07.0 22.3IN V.LAT

U T

M LT

65.4

1636 1642 1648

1630 1636 1642 1648-300

-200

-100

0

100

200

300

By,

nT

1630 16 36 1642 1648-4000

0

4000

8000

12000

16000

P,W

/km

2

Downward (black circles) and upward (white diamonds) turbulent Poynting flux averaged over the polar (left) and auroral (right) latitudes versus Bz IMF.

> 75° 60 ° < < 75°

-12 -8 -4 0 4 8 12BzIM F, nT

-100

0

100

200

300

400

P,

W/k

m2

P downward

P upw ard

-12 -8 -4 0 4 8 12BzIM F, nT

-100

0

100

200

300

P,

W/k

m2

P dow nward

Pupw ard

Poynting flux δP in the auroral zone and the polar cap observed by DE2 on day 316 1981, UT = 00.

Abry P. et al., Wavelets for the analysis, estimation and synthesis of scaling data , in Self-similar Network Traffic and Performance Evaluation, [2000].

Data: dataseries combined from DE2 observations in 10 dawn-to-dusk passes over the

auroral zone and the polar cap (southward Bz IMF).

Findings: (1) similar spectra in both regions; (2) a change in the spectrum slope at scale 32 km

Non-perfect mapping of magnetospheric electric fields down to ionospheric heights? A diffusion range?

Weimer et al., Auroral zone electric fields from DE 1 and 2 at magnetic conjunctions, J. Geophys. Res., 98, A8, 7479-7494, 1985.

Scale-dependent ‘mapping’ function

0y

constP

xEj i

x

P

i

|||||| aVj i

xEaV i

x

P

||

xE

zE zx

In a static case:

Basic equations:

Assumptions:

(1) (2) (3)

(4)

Integrating over z from z = i to z = h, we have

||Vdx

EE hx

ix

(5)

Substitution of (5) into (3) yields

2

2

||202

||2

xVk

xV h

x

P

ak

20(6) where

Expanding the high-altitude potential and electric field in a Fourier series ikxh

kk

hx e )( ikxh

kk

hx eikE

and substituting into Fourier transforms of (5) and (6): ||ikVEE hx

ix h

xkkkV 220

2|| )(

we finally have for each Fourier harmonics with wave number k 20

2

20

kkk

EE

hx

ix

Modeled diffusion range for different k0 values

Alfven wave turbulence

Dubinin E. M. et al., Auroral electromagnetic disturbances at altitudes of 900 km: Alfven wave turbulence,Planet. Space Sci. ,36, N10, 949-962, 1988. Data: ICB-1300, 900 km altitude, f < 6 Hz.

Variations of Ex and By componentsin séance 2931 (2 March 1982).

Power spectra of electric and magnetic fields.

Qualitative scheme of the instability of Alfven wave with a finite amplitude.

Turbulence manifestations in aurora

Auroral observations by ALIS during substorm conditions

Golovchanskaya I. V., B. V. Kozelov, et al. Scaling behavior of auroral luminosity fluctuations observed by AuroralLarge Imaging System (ALIS), J. Geophys. Res., 113, A10303, doi:10.1029/2008JA013217, 2008.

Substorm auroral spots observed in the blue (λ = 4278 Å) emission

Substorm auroral arcs observed in the blue (λ = 4278 Å) emission

Corrections of the scaling characteristics for the effect of aspect angle broadening.

Scaling characteristics of auroral fluctuations in the horizontal plane are distorted because of field-aligned extension of auroral structures, which is determined by a type of precipitation.

Kozelov B. V. and I. V. Golovchanskaya, Effect of the aspect angle broadening on the scaling characteristics of auroral fluctuations, 35th optical meeting, Maynooth, 24-29 August, 2008.

Simulation of aspect angle distortions

• Fractional Brownian motion surface (H=0.3, 0..5, 0.7) was used as a precipitation pattern

• Two types of altitude profile were used: narrow and wide

• Region near magnetic zenith was simulated

No distortion, fBm H=0.3

Narrow profile distortion

Wide profile distortion

• The estimates of H derived in twenty realizations with applying the wavelet estimator [Abry et al., 2000] are found most robust.

• It is shown that the true Hurst exponent H can be derived for self-similar (fractal) auroral data contaminated by the effect of aspect angle broadening. The necessary formulas are provided.

Distorted values ofscaling indices vs.the true ones.

Hurst exponentsdeduced from thescaling indices.

Relations between auroral and electrodynamical scaling parameters

Intensity of auroral luminosity is proportional to the precipitation energy flux: I ~ ε.For monoenergetic precipitation: ε ~ (eV)2 where V is the field-aligned potential drop [Lyons et al., 1979] .Corrected for the effect of aspect angle broadening, scaling index αI = 0.6–0.98 and should be coincident with αV

2. As shown by Lyons et al. [1979] j|| ~ VFrom current continuity equation in case = const αj|| = αE – 1 For substorm conditions [Golovchanskaya et al., 2008] αE ~ 1.2-1.4Then αj|| ~ 0.2-0.4 Finally αV

2 ~ 0.4-0.8 Considering a large number of simplifying assumptions, this is in a reasonable agreement with αI.

Conclusions

For the high-latitude low-frequency (f < i) plasma turbulence it was possible:1. To show the relation to the IMF conditions.2. To demonstrate the coincidence of the occurrence regions in the ILAT-MLT coordinates with the focuses of the large-scale Birkeland currents/convection velocity shears. 3. To provide evidence for the magnetospheric source.4. Using particle precipitation data to discriminate between the turbulence in the auroral zone and the polar cap. 5. By application of a discrete wavelet transform method, developed for the analysis and estimation of scaling data, to find a peculiarity in the turbulence spectrum at f ~ 0.25 Hz (s ~ 30 km), and to show that it cannot be explained as a transition to the diffusion range. 6. To refute the interpretation in terms of electrostatic ionospheric turbulence.7. To consider the finite amplitude Alfvén wave turbulence as a plausible alternative.8. To study turbulence manifestations in the variations of auroral luminosity during substorm conditions with making corrections for aspect angle broadening distortions.9. Under a number of simplifying assumptions, to relate the scaling parameters of electrodynamical and optical turbulent data.

So far unresolved problems

1. A heavy need for higher resolution ( > 16 Hz) simultaneous electric and magnetic field measurements by a low-altitude polar-orbiting spacecraft.2. A plausible interpretation for the higher-frequency spectral range, including the change of the slope at the local I of O+ .3. Interpretation of the seasonal variation in the spectral slopes reported by Heppner et al. [1993]..