ENERGETIC AURORAL ELECTRON DISTRIBUTIONS DERIVED FROM GLOBAL X-RAY MEASUREMENTS AND COMPARISON WITH IN-SITU PARTICLE MEASUREMENTS

On May, 27, 1996, the Polar Ionospheric Xray Imaging Experiment (PIXIE ) on board NASA's POLAR spacecraft was imaging the southern auroral ov al during an auroral substorm, Near simultaneous particle measurements by the DMSP F12 and F13 and POLAR satellites allow us to compare meas ured energetic electron distributions with distributions derived from the x-ray measurements; good agreement is achieved where the assumed e lectron distribution used in the x-ray derivations is a reasonable app roximation 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 dependen ce of the electron drift speed on energy and its dominance over the lo ss rate due to precipitation. Strong pitch angle diffusion in the morn ing sector depletes the source of injected electrons creating the abse nce of significant electron fluxes, and thus x-ray fluxes, above 1.5 k eV in the afternoon sector.