On the importance of IMF |B Y | on polar cap patch formation

1. On the importance of IMF |BY| on polar cap patch formation Qinghe Zhang1, Beichen Zhang1, Ruiyuan Liu1, M. W. Dunlop2, M. Lockwood 2, 3, J. Moen4, Huigen Yang1, Hongqiao Hu1, Zejun Hu1, Shunlin Liu1 , I. W. McCrea2, and M. Lester5 1 SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, China 2 SSTD, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK. 3Space Environment Physics Group, Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, UK 4 Department of Physics, University of Oslo, Blindern, Oslo, Norway 5 Department of physics and Astronomy, University of Leicester, Leicester, UK

2. Outline • Introduction • Observations • Discussion • Conclusion

3. Introduction (1) • Polar cap patches were defined by Crowley [1996] as islands of high density ionospheric plasma surrounded by plasma of half the density or less. • After formation by ionospheric cusp dynamics, the patches follow the convection pattern across the pole from day to night and are pulled into the nightside oval on exiting the polar cap [eg. Buchau et al., 1983;Moen et al., 2006]. Moen et al., 2006

4. Introduction (2) • There are three proposed mechanisms for the production of patches [Moen et al. 2006; Lockwood et al., 2005a,b; Oksavik et al., 2006] : • IMF regulation of the cusp convection pattern, causing alternating intake of high and low density plasma; • Plasma depletion within flow-burst channels due to enhanced recombination associated with newly-opened magnetic flux tubes; • Plasma structuring by transient reconnection where the open closed boundary (OCB) leaps equatorward to a region of higher density plasma, followed by poleward relaxation of that boundary carrying with it the high density plasma accelerated into the polar flow. • Moen et al. [2008b] found that intake of high-density plasma material into the polar cap was independent of IMF BY, but that the direction of the zonal movement of plasma depended on the IMF BY component, giving rise to an MLT asymmetry of occurrence rate around magnetic noon.

5. Introduction (3) OCB motions associated with FTEs (Zhang, et al., JGR, 2010） FTEs The evolutions of a PMAF associate with an FTE PMAFs • A pulse reconnection will leads the open-closed boundary (OCB) eroding to equatorward and then relaxing back to poleward.

6. Introduction (4) FTEs on 1 Apr 2004 (Zhang et al., Ann. Geo., 2008) A series of  FTEs were observed with mixing of magnetosheath and magnetospheric plasma populations Cluster cross through the cusp into the high-latitude dayside plasma sheet, crossing the MP into MSH at about 12:00UT

7. Conjugate SuperDARN observations S N N S Velocity Enhancement Start time 12:48 UT 12:54 UT 12:30 UT 12:32 UT Evolution time 4 - 6 minutes End time 12:36 UT 12:38 UT 12:56 UT 13:02 UT

8. The formation of polar cap patches: a case study (Zhang et al., JGR, 2011) • VHF field-of-view crossed aurora oval and pointed northward in Low elevation (30o) • ESR located in polar cap with a beam pointed north pole in Low elevation (30o) • SuperDARN CUTLASS Finland radar beam 9 also monitored this crossing region

9. IMF and Solar wind conditions Bz <0

10. ESR observations • Clear Poleward-moving plasma concentration enhancements (polar cap “patches”) • Cold plasma inside the polar cap patches

11. EISCAT VHF observations • Poleward-moving flow but thinner than that seen by ESR 32m radar • Electron temperature much higher above the OCB • Some structures cross the OCB with poleward-moving features OCB

12. SuperDARN CUTLASS Finland radar observations • Clear PMRAFs • Anti-sunward flows with PIFs • Cusp feature below about 76o

13. Discussion • 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

14. DiscussionComparison to the observations from the three radars

15. Discussion • Model explanation of the formation of polar cap patches and Tongue Of Ionization (TOI) • Reconnection occurred at different location • Outside ones are faster than the inner ones Lockwood et al., 2000

16. Photoionisation effect Intermittent injection of photoionisation-enhanced plasma into the polar cap opened by burst reconnection Tongue Of Ionization (TOI) Enhanced the Ne observed by ESR

17. Plasma 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

18. Conclusion • We present a number of poleward-moving events observed ESR, VHF Radar and CUTLASS Finland radar between 11:30-13:00 UT on 11 Feb 2004, when the IMF is dominated by southward components. • These events appeared quasi-periodically with a period of about 10 minutes. • Comparison to the observations from these three radars, we found that there is clear one-to-one correspondence between the PMPCEs observed by ESR, VHF radar and the PMRAFs measured by CUTLASS Finland radar. These indicated that poleward-moving events were generated by photoionisation and convected into the polar cap when bursts of reconnection opened them. • There is clear evidence that plasma structuring into patches was dependent on the variability in IMF |BY|. • The average duration of these events imply that the average evolution time of the newly open flux tube is about 33 minutes.

21. The end. • Thank you for your attention!!!