Auroral signatures of localized reconnection near the poleward edge of a dense
plasma sheet

W.S. Lewis, J.L. Burch, D.G. Mitchell, S.B. Mende, R.A. Heelis, H. Frey, 
S.A. Fuselier, M.F. Thomsen, K. Retherford


Unusual bright, localized auroral emissions well poleward of the main auroral
oval were observed by the IMAGE Far-Ultraviolet (FUV) instrument during two
consecutive auroral events that occurred late in the day on 25 September 2001
during a period of increased solar wind dynamic pressure following the arrival 
of an interplanetary shock. Bz was generally southward during the two events, 
except for a ~20-minute northward excursion, and By was predominantly negative. 
The bright spots were seen in both the electron and proton channels of the FUV
Spectrographic Imager (SI13 and 12, respectively) as well by the Wideband 
Imaging Camera (WIC). The bright spots occurred near the poleward edge of an
emission-filled region that extended to high-latitudes (>80 deg). They were not
stationary but moved sunward during the first event and antisunward during the
second.  In the latter event, they appeared together with localized brightenings
in the dayside main oval and moved in concert with them.  Bursts of energetic
(138-222 keV) O+ were observed by the IMAGE High-Energy Neutral Atom (HENA)
imager at the same time that FUV observed the high-latitude bright spots and
while the spacecraft was located on field lines that map to the emission regions.
The high-latitude bright spots, which appear near the boundary between open and
closed field lines, are likely excited by energetic particles from the plasma
sheet boundary layer, including energetic O+, that have been accelerated by
reconnection in the distant tail. The simultaneous appearance and coordinated
motion of the high-latitude bright spots and companion spots on the main oval
during the second event can be accounted for by the "reclosure" scenario
suggested by Reiff and Burch [1985].

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002