Global multispectral auroral imaging of an isolated substorm

We analyze simultaneous visible, ultraviolet (UV), and X-ray auroral images of an isolated substorm on January 25, 1998. The total precipitating elect ron energy flux and mean energy extracted near substorm maximum from each o f the imagers are in acceptable agreement. The expansion phase visible, UV, and Xray emissions are morphologically similar, with the brightest emissio ns coming from the auroral surge. However, during the recovery phase, there are regions of bright X-ray emissions near local midnight and dawn that do not correspond to obvious features in the visible and UV images. X-ray ene rgy analysis in these regions reveals a high energy (similar to 30-100 keV) component of the precipitating electron population that contributes simila r to 30% of the total electron energy flux. The temporal development of the X rays indicates that the dawn emissions originate in a drifting electron population, while the newly revealed midnight emissions originate in a cont inuous injection of energetic electrons in a narrow local time region.