Transpolar exospheric plasma: 1. Plasmasphere termination

Abstract

From an examination of many transpolar exospheric electron concentration distributions along tracks of the Alouette 1 satellite at a fixed direction to the earth-sun line, it is found that there is an approximately characteristic profile for a given direction. It is suggested that this implies a fixed concentration distribution over the polar regions under which the earth rotates. If it is assumed that the ionospheric trough at high latitudes is a demarcation between solar-produced ionization lying inside the plasmasphere and aurorally associated ionization at high latitudes, the midlatitude termination is the low-latitude wall of the trough. From a study of many topside sounder records obtained during the polar winter, the position of this termination is located at the F peak at all local times, and its motions investigated. Its position is found to be most clearly defined and correlated with Kp in the 1800 LT region, when the plasmapause is most unstable. However, when the trough is compared with the position of the plasmapause projected back along field lines, systematic differences in position are apparent that may be related to field line distortions in the magnetosphere.