Quantitative simulation of a magnetospheric substorm 3. Plasmaspheric electric fields and evolution of the plasmapause

Abstract

Results of the Rice University substorm simulation have been used to investigate the penetration of substorm‐associated electric fields into the plasmasphere. Near 4 RE in the equatorial plane, our time dependent electric field model is characterized by eastward components in the dusk‐midnight local time sector and westward components after midnight. Except for a small region just before dusk, the model predicts eastward electric field components throughout the daytime sector. The characteristic radial component is directed inward at all local times except for a small region just after dawn. These results compare favorably with available whistler and incoherent‐scatter radar measurements obtained during magnetically disturbed periods. By assuming an initial plasmapause shape and by following the computed drift trajectories of plasma flux tubes from that initial boundary we have examined the short term evolution of the plasmapause during the substorm‐like event of September 19, 1976. We find that narrow filamentary tails can be drawn out from the plasmasphere near dusk within hours of substorm onset. These tail‐like appendages to the plasmasphere subsequently drift rapidly from the dusk sector toward the daytime magnetopause. Investigation of the large‐scale time dependent flow of plasma in the evening sector indicates that some mid‐latitude plasma flux tubes that drift eastward past the dusk terminator reverse their motion between dusk and midnight and begin to drift westward toward dusk. Such time dependent changes in flow trajectories may be related to the formation of F region ionization troughs.