SIGNATURES OF ENERGY-TIME DISPERSED ELECTRON-FLUXES MEASURED BY FREJA

Two measurements of velocity-dispersed electron fluxes at altitudes near 1750 km are reported. The energy-time signatures of both observations are interpreted in terms of a simple time-of-flight (TOF) scenario. The first measurement occurred at low magnetic latitude (approximately 62-degrees) and consisted of three injection events. Analysis yields a source location near the equator approximately 6.5 R(E) from the spacecraft and provides evidence that the injections were periodic. The injections are interpreted as being the result of interactions with waves near the earthward edge of the equatorial plasma sheet, and the presence of fine structure in the fluxes with timescales of a few hundred ms provides new information on the injection process. Analysis of the second measurement leads to the determination of a source location about 850 km above the spacecraft. Although the simple model is able to explain the observations at small pitch angles, the measurements at large pitch angles require that the model be refined, and a modification which invokes pitch-angle diffusion is suggested.