Statistical behavior of proton and electron auroras during substorms

B. J. Morsony, S. B. Mende, H. U. Frey, and T. J. Immel   


The IMAGE FUV imager can provide global maps of electron and proton 
precipitation and it is possible to observe how these maps change as a 
result of substorms.  The large body of IMAGE FUV data permits the 
performance of a superimposed epoch analysis for many substorms.  For each 
substorm the onset locations and times were determined from the Wideband 
Imaging Camera (WIC) images which represent mainly electron auroras.  For 
the superimposed epoch analysis the WIC (electron) and Spectrographic 
Imager SI12 (proton) images were transformed into rectangular magnetic 
latitude (MLAT) and magnetic local time coordinates (MLT).  Each event was 
plotted on a time scale related to the time of onset and the MLT scale was 
shifted until the onset point of each substorm was lined up at 0 relative 
magnetic local time (RMLT).  A double Gaussian was then fitted to the data 
at RMLT of -4,-2,0,+2,+4 by representing the auroral intensity, I, as a 
function of MLAT.  From the Gaussian coefficients we were able to obtain 
the mean of the peak auroral intensities, the mean location of the maximum 
intensity, and the mean position of the poleward and equatorward boundary 
of the proton and electron precipitation.  From 91 substorms we derived 
some statistically meaningful quantities.  We showed that pre-substorm 
there is an equatorward motion of the equatorward boundary of the electron 
and proton aurora.  At onset the proton auroral peak intensity increases 
only by a factor of two compared to a factor of 5 for the electrons.  
There is rapid poleward expansion of the proton aurora after onset which 
slows down after the first few minutes.  The electron onset continues 
towards higher latitudes.  The relative position of the proton and 
electron aurora and their boundaries was investigated for various RMLT 
during substorm phases.

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