VLF plasmaspheric emissions—‘wave’ signatures of inner magnetosphere boundaries

Abstract

VLF quarter-gyrofrequency emissions have been observed in the plasmasphere by low-altitude (up to 2500 km) Intercosmos satellites. Their experimental characteristics indicate that the origin and the distribution function of resonant electrons and the type of instability leading to their production can differ during various phases of magnetospheric disturbances. Their close connection to the earthward edge of the lowest energy plasma sheet electron fluxes during active periods is shown. During recovery periods following magnetospheric substorms, they persist (together with other symptoms of a certain internal plasmaspheric structure—subauroral T e -peaks, SAR arcs, etc.) at roughly the same L-value within the new, more distant plasmapause. A new kind of instability is mentioned which could lead to their production during the recovery phase of magnetospheric substorms.