The substorm evolution was studied by performing a superposed epoch analysis of 91 substorms using IMAGE FUV data. Onset locations and times were determined from images produced by the Wideband Imaging Camera (WIC) usually dominated by electron aurora. Images taken by WIC and by the Spectrographic Imager SI12 channel, responsive to proton aurora, were transformed into rectangular magnetic latitude (ML) and magnetic local time (MLT) coordinates and plotted on a timescale related to the time of substorm onset (T = 0) and to a Relative MLT (RMLT) normalized to onset MLT. A double Gaussian was fitted to the auroral intensity data as a function of ML at RMLT of -4, -2, 0, +2, and +4. From the Gaussian coefficients the means of several parameters were plotted as a function of time. Presubstorm, there was an equatorward motion of the mean low-latitude boundary of the electron and proton aurora. There was no evidence of preonset auroral fading in the mean intensity. At onset the proton auroral peak intensity increased only by a factor of 2 compared with ~5 for the electrons. At RMLT = 0, rapid poleward expansion of the proton aurora after onset occurred. The proton expansion slowed down after the first few minutes, while the electron surge continued toward higher latitudes. The mean poleward expansion of the electron aurora reached about 3.5¿ in 5 min and reached a total expansion of 5.5¿ in an hour. The protons expanded about 2.5¿ in 5 min and expanded about 3¿ one hour after onset. The latitude width of the aurora increased at onset due to both a large poleward and a moderate equatorward expansion. There appeared to be stronger substorm-related activity in the local time range toward dawn than toward dusk. In the RMLT sector duskward of onset the proton auroras were located equatorward of the electrons and poleward in the dawnward RMLT sector.