Statistical Behavior of Proton and Electron Auroras During Substorms

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.