On the importance of IMF |BOn the importance of IMF |BYY| |

on polar cap patch formationon polar cap patch formation Qinghe ZhangQinghe Zhang11, Beichen Zhang, Beichen Zhang11, Ruiyuan Liu, Ruiyuan Liu11, M. W. , M. W. DunlopDunlop22, M. Lockwood , M. Lockwood 2, 32, 3, J. Moen, J. Moen44, Huigen Yang, Huigen Yang11, H, Hongqiao Huongqiao Hu11, Zejun Hu, Zejun Hu11, Shunlin Liu, Shunlin Liu11 , I. W. McCrea , I. W. McCrea22, ,

and M. Lesterand M. Lester55

1 SOA Key Laboratory for Polar Science, Polar Research Institute 1 SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, Chinaof China, Shanghai, China

2 SSTD, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfords2 SSTD, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK.hire, OX11 0QX, UK.

33 Space Environment Physics Group, Department of Meteorology, Space Environment Physics Group, Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB,

UKUK4 Department of Physics, University of Oslo, Blindern, Oslo, Norw4 Department of Physics, University of Oslo, Blindern, Oslo, Norw

ayay 5 Department of physics and Astronomy, University of Leicester, 5 Department of physics and Astronomy, University of Leicester,

Leicester, UKLeicester, UK

OutlineOutline IntroductionIntroduction

ObservationsObservations

DiscussionDiscussion

ConclusionConclusion

Introduction (1)Introduction (1) Polar cap patches were defined by Crowley [1996] Polar cap patches were defined by Crowley [1996]

as islands of high density ionospheric plasma surras islands of high density ionospheric plasma surrounded by plasma of half the density or less.ounded by plasma of half the density or less.

After formation by ionospheric cusp dynamics, thAfter formation by ionospheric cusp dynamics, the patches follow the convection pattern across the e patches follow the convection pattern across the pole from day to night and are pulled into the nigpole from day to night and are pulled into the nightside oval on exiting the polar cap [eg. htside oval on exiting the polar cap [eg. Buchau et aBuchau et al., 1983;l., 1983; Moen et al., 2006Moen et al., 2006 ].].

Moen et al., 2006Moen et al., 2006

Introduction (2)Introduction (2) There are three proposed mechanisms for the production of patcThere are three proposed mechanisms for the production of patc

hes [Moen et al. 2006; Lockwood et al., 2005a,b; Oksavik et al., 200hes [Moen et al. 2006; Lockwood et al., 2005a,b; Oksavik et al., 2006] : 6] :

(1)(1) IMF regulation of the cusp convection pattern, causing alternatinIMF regulation of the cusp convection pattern, causing alternating intake of high and low density plasma;g intake of high and low density plasma;

(2)(2) Plasma depletion within flow-burst channels due to enhanced recPlasma depletion within flow-burst channels due to enhanced recombination associated with newly-opened magnetic flux tubes;ombination associated with newly-opened magnetic flux tubes;

(3)(3) Plasma structuring by transient reconnection where the open closPlasma structuring by transient reconnection where the open closed boundary (OCB) leaps equatorward to a region of higher densited boundary (OCB) leaps equatorward to a region of higher density plasma, followed by poleward relaxation of that boundary carryy plasma, followed by poleward relaxation of that boundary carrying with it the high density plasma accelerated into the polar flow.ing with it the high density plasma accelerated into the polar flow.

Moen et al. [2008b] found that intake of high-density plasma mateMoen et al. [2008b] found that intake of high-density plasma material into the polar cap was independent of IMF BY, but that the dirrial into the polar cap was independent of IMF BY, but that the direction of the zonal movement of plasma depended on the IMF BY ection of the zonal movement of plasma depended on the IMF BY component, giving rise to an MLT asymmetry of occurrence rate acomponent, giving rise to an MLT asymmetry of occurrence rate around magnetic noon. round magnetic noon.

The evolutions of a PMAF associate with an FTE

Introduction (3)OCB motions associated with FTEs (Zhang, et al., JGR, 2010 ）

FTEs

A pulse reconnection will leads the oA pulse reconnection will leads the open-closed boundary (OCB) eroding tpen-closed boundary (OCB) eroding to equatorward and then relaxing baco equatorward and then relaxing back to poleward.k to poleward.

PMAFs

Introduction (4)FTEs on 1 Apr 2004 FTEs on 1 Apr 2004

(Zhang et al., Ann. Geo., 2008)

Cluster cross through the cusp into the high-latitude dayside plasma sheet, crossing the MP into MSH at about 12:00UT

A series of  FTEs were observed with mixing of magnetosheath and magnetospheric plasma populations

12:30 UT

12:36 UT

12:38 UT

Velocity Enhancement

Start time

12:32 UT

N S

End time

12:48 UT

12:54 UT

12:56 UT

13:02 UT

N S

Conjugate SuperDARN observations

Evolution time 4 - 6 minutes

The formation of polar cap patches: a The formation of polar cap patches: a case study case study (Zhang et al., JGR, 2011)(Zhang et al., JGR, 2011)

VHF field-of-view crossed aurora oval and pointed northward in Low elevation (30VHF field-of-view crossed aurora oval and pointed northward in Low elevation (30oo)) ESR located in polar cap with a beam pointed north pole in Low elevation (30ESR located in polar cap with a beam pointed north pole in Low elevation (30oo)) SuperDARN CUTLASS Finland radar beam 9 also monitored this crossing regionSuperDARN CUTLASS Finland radar beam 9 also monitored this crossing region

IMF and Solar wind IMF and Solar wind conditionsconditions

Bz <0

ESR ESR observatioobservatio

nsns Clear PolewarClear Polewar

d-moving plasd-moving plasma concentratima concentration enhancemeon enhancements (polar cap nts (polar cap “patches”) “patches”)

Cold plasma Cold plasma inside the inside the polar cap polar cap patchespatches

EISCAT VHF EISCAT VHF observationsobservations

Poleward-moviPoleward-moving flow but thing flow but thinner than that nner than that seen by ESR 32seen by ESR 32m radarm radar

Electron tempeElectron temperature much hirature much higher above the gher above the OCBOCB

Some structureSome structures cross the OCB s cross the OCB with poleward-with poleward-moving featuremoving featuress

OCB

SuperDARN CUTLASS Finland SuperDARN CUTLASS Finland radar observationsradar observations

Clear PMRClear PMRAFsAFs

Anti-sunwAnti-sunward flows ard flows with PIFswith PIFs

Cusp featuCusp feature below are below about 76bout 76oo

DiscussionDiscussion

The trough of electron density formed by the plasma convection from nightside

Polar cap extending after dayside reconnection occurred.

Poleward-moving ionospheric flows were enhanced associated with the burst reconnections

DiscussionDiscussionComparison to the observations from the Comparison to the observations from the

three radarsthree radars

DiscussioDiscussionn Model explanation of Model explanation of

the formation of polar the formation of polar cap patches and cap patches and Tongue Of Ionization (TOI)

Reconnection occurred Reconnection occurred at different locationat different location

Outside ones are faster Outside ones are faster than the inner onesthan the inner ones

Lockwood et al., 2000

Photoionisation effectPhotoionisation effect

Intermittent injectIntermittent injection of photoionisation of photoionisation-enhanced plasion-enhanced plasma into the polar cma into the polar cap opened by bursap opened by burst reconnectiont reconnection

Tongue Of Ionization (TOI)Enhanced the Ne observed by ESR

Plasma convection effectPlasma convection effect

However, the trough of electron density formed by the plasma convection from nightside

This confirm our VHF radar observations.

The electron density in F region obtained from ionospheric simulation by Dr. Zhang

ConclusionConclusion We present a number of poleward-moving events obserWe present a number of poleward-moving events obser

ved ESR, VHF Radar and CUTLASS Finland radar betweved ESR, VHF Radar and CUTLASS Finland radar between 11:30-13:00 UT on 11 Feb 2004, when the IMF is domien 11:30-13:00 UT on 11 Feb 2004, when the IMF is dominated by southward components. nated by southward components.

These events appeared quasi-periodically with a period These events appeared quasi-periodically with a period of about 10 minutes. of about 10 minutes.

Comparison to the observations from these three radarComparison to the observations from these three radars, we found that there is clear one-to-one correspondens, we found that there is clear one-to-one correspondence between the PMPCEs observed by ESR, VHF radar ance between the PMPCEs observed by ESR, VHF radar and the PMRAFs measured by CUTLASS Finland radar. Thd the PMRAFs measured by CUTLASS Finland radar. These indicated that poleward-moving events were generaese indicated that poleward-moving events were generated by photoionisation and convected into the polar cap ted by photoionisation and convected into the polar cap when bursts of reconnection opened them. when bursts of reconnection opened them.

There is clear evidence that plasma structuring into patThere is clear evidence that plasma structuring into patches was ches was dependent on the variability in IMF |Bdependent on the variability in IMF |BYY|.|.

The average duration of these events imply that the aveThe average duration of these events imply that the average evolution time of the newly open flux tube is about rage evolution time of the newly open flux tube is about 33 minutes.33 minutes.

The end.The end.

Thank you for your Thank you for your attention!!!attention!!!