Energetic auroral electron distributions derived from global X-ray measurements and comparison with in-situ particle measurements

On May, 27, 1996, the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) on board NASA's POLAR spacecraft was imaging the southern auroral oval during an auroral substorm. Near simultaneous particle measurements by the DMSP F12 and F13 and POLAR satellites allow us to compare measured energetic electron distributions with distributions derived from the x‐ray measurements; agreement is achieved where the assumed electron distribution used in the x‐ray derivations is a reasonable approximation to the measured distribution. The PIXIE data show an energy dispersion in the precipitating electrons in the morning sector such that energy increases with increasing MLT, the result of the dependence of the electron drift speed on energy and its dominance over the loss rate due to precipitation. Strong pitch angle diffusion in the morning sector depletes the source of injected electrons creating the absence of significant electron fluxes, and thus x‐ray fluxes, above 1.5 keV in the afternoon sector.