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Magnetic Connectivity and Suprathermal Electron Distribution in Solar Wind Reconnection Events: STEREO/SWEA

This study focuses on the analysis of magnetic connectivity and suprathermal electron distribution in solar wind reconnection events using data from the STEREO/SWEA instrument. The preliminary inter-anode and inter-deflection calibrations have been done and the pitch angle distributions appear to be compatible in a relative sense. However, more refinements and absolute calibrations are still needed. The study also explores the change in connectivity between widely separated spacecraft and the potential disappearance of the strahl in reconnection events.

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Magnetic Connectivity and Suprathermal Electron Distribution in Solar Wind Reconnection Events: STEREO/SWEA

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  1. Benoit Lavraud,1 Andrea Opitz,1Jack Gosling,2 J.-A. Sauvaud,1and the IMPACT team1,3,4,51: CESR/CNRS, Toulouse, France2: LASP, Boulder, Colorado, USA3: SSL, U. Berkeley, USA4: UCLA, Los Angeles, USA5: NASA/GSFC, Maryland, USA, … Magnetic connectivity associated with SW reconnection events: STEREO/SWEA

  2. The STEREO Solar Wind Electron Analyzer (SWEA) instrument • SWEA instruments identicalon ST-A and B • Preliminary inter-anode and inter-deflection calibrations • Pitch angle distributions should be OK in relative sense • Refinements still to be done, as well as absolute calibrations TOSUN Solar wind Solar Wind e- Electrostatic deflector Electrostatic analyzer

  3. Suprathermal (>200 eV) electrons are very fast: 1AU in a matter of hours •  Magnetic topology • Check whether pitch angle distributions are compatible at ACE and STEREO • The case of solar wind reconnection events is most useful: complex and variable PADs over short periods MOTIVATION : Solar wind Heliospheric Current Sheet (HCS) [Gosling et al., 2005; 2006]

  4. Spacecraft locations on March 31, 2007 HCS = Heliospheric current sheet SUN Solar wind No SWEA dataat STEREO Aunfortunately

  5. HCS reconnection layer at ACE/WIND HCS Solar wind

  6. HCS reconnection layer at ACE/WIND RED: distribution inside the layer Solar wind  ACE & WIND are Sunward of X-line on closed field lines connected to the Sun

  7. Heliospheric current sheet reconnection layer at ST-B (Arb. Units) Solar wind Reconnection layer  Marked differences in pitch angle distrib. inside the layer

  8. Closed field lines observed at STEREO-B as well Note: Absolute PSD values are off, but relative behavior is meaningful Red: PAD inside layer Solar wind (Arb. Units)  ST-B also sunward of X-lineNext: find event with X-line in between…

  9. Closed field lines observed at STEREO-B as well (Arb. Units) Solar wind Mixed suprathermal electrons not bound to the layer Reconnection layer  Evidence for the separatrix layer outside the exhaust

  10. Closed field lines observed at STEREO-B as well Solar wind Suprathermal electrons from the other side • The existence of separatrix layers is confirmed for this event, although it is not always observed (?)

  11. Some topics of interest • Continuous nature of reconnection • X-line spatial extent • Particle acceleration/heating at X-line • Particle heating at exhaust boundaries All of the above potentially different at Earth’s magnetosphere !?

  12. CONCLUSIONS : • Although additional corrections are still to be done, SWEA pitch angle data are meaningful • The case of solar wind reconnection events is most useful for that purpose: complex and variable • SWEA observations of high energy electron leakage confirm that the boundaries of the reconnection layer are open, as expected • Other interesting topic: Is heating occurring at the boundaries? Different from Earth’s magnetopause? Solar wind

  13. MOTIVATION : • Check whether pitch angle distributions are compatible at ACE and STEREO • The case of solar wind reconnection events is most useful: complex and variable • We may observe the change in connectivity between widely separated spacecraft • For reconnection events in between the spacecraft we may contribute to the debate about strahl disappearance Solar wind [Gosling et al., 2005; 2006; Crooker and Pagel, 2008]

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