Global Multispectral Auroral Imaging of an Isolated Substorm

Abstract. We analyze simultaneous visible, ultraviolet (UV), and X-ray auroral images of an isolated substorm on January 25, 1998. The total precipitating electron energy flux and mean energy extracted near substorm maximum from each of the imagers are in acceptable agreement. The expansion phase visible, UV, and Xray emissions are morphologically similar, with the brightest emissions 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 energy analysis in these regions reveals a high energy (∼30–100 keV) component of the precipitating electron population that contributes ∼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 continuous injection of energetic electrons in a narrow local time region.