Plasma injection events at synchronous orbit related to positive DST

Abstract

Synchronous orbit measurements from the University of New Hampshire ATS 6 instrument have been compared with several other types of space and ground data in a study of the plasma effects related to SI and SC (positive excursions of Dst) magnetic perturbations. It is found that plasma injections at synchronous orbit, related to SI and SC, are very similar to plasma injections associated with substorms, except that the former occur at all local times. These injections can be interpreted as the co‐location of particle boundaries on an inward propagating front. The boundaries are those due to magnetospheric convection and precipitation losses and normally are spatially dispersed as a function of energy. The compression magnetic pulse associated with SI and SC events is apparently responsible for the co‐location of these boundaries and their inward propagation. The +Dst magnetic pulse plays a role similar to that of the magnetic tail reconfiguration pulse associated with substorms. Theories of convection in steady state magnetic fields cannot account for the dispersionless character of the injection front. The electron plasma behind the injection front is a hot Maxwellian for local evening +Dst plasma events as is the case for substorms. +Dst‐related injections observed on the dayside have enhanced low‐energy electron intensities, perhaps owing to an ionospheric component. The plasma observed behind the front appears to be hot tail plasma convected to its point of observation. We show evidence that +Dst enhances magnetospheric convection independent of interplanetary magnetic field direction. Since +Dst does not necessarily trigger substorms, enhanced convection is apparently not a sufficient condition for substorm generation.