A MULTIEVENT STUDY OF BROAD-BAND ELECTRONS OBSERVED BY THE DMSP SATELLITES AND THEIR RELATION TO RED AURORA OBSERVED AT MIDLATITUDE STATIONS

Broadband electrons during magnetic storms are characterized by an unu sually intense flux of precipitating electrons in the broadband energy range from 30 eV to 30 keV near the equatorward edge of the auroral o val (47 degrees-66 degrees magnetic latitude). Broadband electrons wer e first reported by Shiokawa et al. [1996]. In this paper, we report a multievent study of broadband electrons, using particle data obtained by the Defense Meteorological Satellite Program (DMSP) satellites dur ing 23 magnetic storms from January 1989 through May 1992. Twelve broa dband electron events are identified. Most of them are observed in the night sector, but some are observed in the morning sector. Particle d ata for successive polar passes of the DMSP multisatellites are used t o show that broadband electrons generally last for less than 30 min an d that for some events, they precipitate over a wide range of local ti mes simultaneously. On the basis of a quantitative calculation of opti cal emissions from electrons in the neutral atmosphere, we conclude th at broadband electrons are a possible cause of red auroras observed at midlatitude ground stations. We suggest that broadband electrons are associated with certain substorms during the main phase of magnetic st orms. This conjecture comes from observations of H component positive bays and Pi 2 pulsations observed at low-latitude magnetic stations an d from magnetic field variations observed at geosynchronous satellites . We conclude that the magnetospheric source of broadband electrons li es within the inner part of the plasma sheet. This conclusion is based on the facts that broadband electrons appear in latitudes where plasm a sheet particles were observed before the event and that broadband el ectrons are observed poleward of the subauroral ion drifts, a position that corresponds to the inner edge of the injected particle layer dur ing storms. High-energy particle data obtained at geosynchronous satel lites show that both strong magnetopause compressions in the dayside a nd decrease of the particle fluxes in the nightside occur in associati on with the broadband electron events. Possible mechanisms of broadban d electron production are discussed.