Global cause of localized high latitude aurora

H.U. Frey, S.B. Mende, T.J. Immel, G. Lu, N. Ostgaard


The FUV instrument on IMAGE frequently observes a very localized, spot-like
aurora at high latitudes poleward of the dayside auroral oval and the cusp.
The absence of simultaneous proton aurora suggests a pure electron 
precipitation, which was confirmed by a few conjugate FAST observations.  
This aurora occurs during northward IMF conditions with very low solar wind 
density (dynamic pressure).  Additionally, there is a preference of 
negative IMF B_x conditions, and B_y has to be positive.  These external 
conditions suggest reconnection at the high latitude magnetopause as the 
driving mechanism for this phenomenon.  During the first two years of 
IMAGE-FUV operations a clear seasonal dependence was found with frequent 
and long-lasting occurrence of the spot-like aurora during northern 
hemisphere summer, and extremely few events during northern winter.  We 
will describe how the seasonal changes of the dipole tilt, solar 
illumination and ionospheric conductivity influence the local occurrence
and intensity of the electron precipitation.

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