Longitudinal drift of substorm electrons as the reason of impulsive precipitation events and VLF emissions

摘要

Using the data from satellite CRRES and threegeostationary LANL spacecraft, the propagation of an electron cloud frommidnight to the evening sector is investigated. An electron cloud wasinjected during a weak isolated substorm that developed on a quietgeomagnetic background. It is found that within the local time sector from03:00 until at least 08:00 MLT, the propagation of electrons at perpendicularpitch-angles is well described by a simple model of drift in the dipolemagnetic field. The flux levels in the field-aligned electrons increasesimultaneously with the flux at perpendicular pitch angles, which isattributed to the pitch angle diffusion by the whistler mode. This pitch-anglediffusion leads to precipitation of electrons from a drifting cloud and anincrease in the ionospheric electron density, simultaneously observed aboveTroms?, Norway, by the EISCAT UHF radar in the morning sector(04:40–05:25 MLT). The precipitation develops as quasi-periodic pulses with a period ofabout 100 s. We discuss the models of pulsating precipitation due to thewhistler cyclotron instability and show that our observations can beexplained by such a model.