Hemispheric Comparison of Signatures of Flux Transfer Events

1. Hemispheric Comparison of Signatures of Flux Transfer Events Kathryn McWilliams and Matt WesselUniversity of Saskatchewan Physics & Engineering Physics, University of Saskatchewan

2. FTE Models From Scholer, 1995 Physics & Engineering Physics, University of Saskatchewan

3. FTEs at the Magnetopause bipolar field variation (Russell & Elphic, 1979)

4. Flux Transfer Events at the Magnetopause (Neudegg et al., 2001) bipolar boundary-normal FTE signatures Magnetopause (Equator-S) Ionosphere (SuperDARN) poleward moving radar auroral forms (PMRAFs) Physics & Engineering Physics, University of Saskatchewan

5. Poleward Moving Radar Patches (STARE) • poleward moving patches during Aug 28, 1978, storm • patches emanate from polar cap boundary (Sofko et al., 1979; 1985) Physics & Engineering Physics, University of Saskatchewan

6. STARE Patches & GEOS-2 M’pause Crossings upwelling ions GEOS-2 footprint in patch GEOS-2 footprint poleward of patch 10X fewer upwelling ions (Sofko et al., 1979; 1985) Physics & Engineering Physics, University of Saskatchewan

7. Pulsed Ionospheric Flows (PIFs) vs. PMRAFs discrete poleward moving patches (with data gaps) PMRAFs PIFs oscillating flow magnitude (with continuous data) Physics & Engineering Physics, University of Saskatchewan

8. MHD Simulation – No Dipole Tilt • Raeder, Annales Geophysicae, 2006 • “Stagnation line” – separates northward and southward flow • Relatively smooth flow away from subsolar point (Earth-Sun line) • No evident plasmoids • Reconnection relatively smooth Physics & Engineering Physics, University of Saskatchewan

9. MHD Simulation – Large Dipole Tilt • Raeder, Annales Geophysicae, 2006 • “Stagnation line” located off Earth-Sun line, towards winter hemisphere • Reconnection X-line forms winter-ward of Sun-Earth line • Plasmoid forms in region of flow towards winter cusp • Field lines draped around plasmoid from summer cusp form second X-line • Plasmoid moves towards winter cusp • No plasmoid observed in summer hemisphere Physics & Engineering Physics, University of Saskatchewan

10. 3D Simulations – Development Along Magnetopause • Raeder, Annales Geophysicae, 2006 Physics & Engineering Physics, University of Saskatchewan

11. 2-D Electric Field in Footprint of Reconnection • Patch of SuperDARN backscatter: • footprint of reconnected field lines • measured by two overlapping SuperDARN radars (CUTLASS) • Compared patch motion to ExB drift (McWilliams et al., 2001) Physics & Engineering Physics, University of Saskatchewan

12. 2-D Electric Field in Footprint of Reconnection • patch expands and moves azimuthally • convection speed differs from patch motion at first Physics & Engineering Physics, University of Saskatchewan

13. 2-D Electric Field in Footprint of Reconnection • Two phases of motion: (1) reconnection (2) convection • FTEs are not necessarily “small” 1 2 Physics & Engineering Physics, University of Saskatchewan

14. Recent Observations • Korotova & Sibeck, GRL, 2008 • Considered m’pause crossings • Interball-1 on dayside only during northern summer months; north=summer, south=winter • Included only FTEs during neg. IMF Bz • Bz < -1 nT • Interball-1 FTEs observed exclusively in WINTER hemisphere Physics & Engineering Physics, University of Saskatchewan

15. Signatures of FTEs McWilliams et al., AG, 2004 Geotail FTEs SuperDARN poleward moving forms 18 Jan 1999 (NH winter) 4 hours UT Physics & Engineering Physics, University of Saskatchewan

16. Survey of Poleward Moving Radar Auroral Forms • only examined poleward moving forms (PMRAFs) • no modulated continuous drifts (PIFs) • Radar Frequency is important! • Before 2002 used single day and single night transmitter frequency • Con: You have to be lucky to get good propagation • Pro: Motion of patches is geophysical frequency change Physics & Engineering Physics, University of Saskatchewan

17. Survey of SuperDARN PMRAFs • Noted days when PMRAFs evident (visual inspection) • viewing angle important Physics & Engineering Physics, University of Saskatchewan

18. Comparing N&S Hem. • The “one hope” frequency makes things difficult • Not guaranteed that radio wave will refract enough to scatter back from cusp/mantle patches Kerguelen = SH Ker Han Hankasalmi = NH Physics & Engineering Physics, University of Saskatchewan

19. Question Answered! • …sort of • Simultaneous poleward moving form in winter and summer hemisphere • This is RARE Physics & Engineering Physics, University of Saskatchewan

20. Seasonal Dependence? • Hankasalmi data only • Does not run “sounding” mode, so patch motion is geophysical • Visual inspection of PMRAFs over nearly a full solar cycle • 1997 – 2006 • FTE: 1893 days • No FTE: 3468 days (~35% FTE) Physics & Engineering Physics, University of Saskatchewan

21. Probably Not… • Our day-frequency is not optimized for season • So we take what we can get • The number of days with FTEs strongly resembles the amount of ionospheric backscatter overall throughout the year • No seasonal trend in SuperDARN PMRAFs Physics & Engineering Physics, University of Saskatchewan

22. Summary and Future Work • Study motivated by simulations and observations of FTEs in winter hemisphere • Modelled plasmoids form in on winter side of Sun-Earth line • Modelled plasmoids carried through winter cusp • FTEs detected in winter hemisphere by Interball-1 • Reconnection footprint should map to both hemispheres, so particles are expected to precipitate into both hemispheres, regardless of where plasmoid forms • SuperDARN does not see seasonal dependence on occurrence of PMRAFs • Simultaneous observations by Hankasalmi and Kerguelen • More sophisticated analysis of statistics is required • More detail on duration of PMRAFs, beams involved, etc. • Relationship to upstream IMF orientation Physics & Engineering Physics, University of Saskatchewan

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24. FTEs (McWilliams et al., 2004) IMF By • FTEs observed at Geotail only under certain IMF conditions (+By and +Bz). • SuperDARN transients suggest FTEs occurred at all times, regardless of IMF orientation. IMF Bz Geotail SuperDARN PMRAFs Physics & Engineering Physics, University of Saskatchewan

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