A correlated study of ELF waves and electron precipitation on Ogo 6

Abstract

The Ogo 6 ELF chorus records from the search coil magnetometer have been compared with simultaneous electron precipitation records. The chorus signals observed in the vicinity of field lines passing through the outer magnetosphere were characteristically accompanied by electron precipitation in the same region. Both the chorus and the precipitation records consisted of a series of sharp peaks. Although in some cases chorus and precipitation peaks appeared to be associated, the observed peaks did not in general coincide. Comparison of the chorus measurements on Ogo 6 and Ogo 5 suggests a model in which the chorus is ducted along field lines to within less than 1 RE above the Ogo 6 orbit after which it diverges from the field lines and is deflected toward the local vertical. The result is equatorward skewing of the average wave pattern with respect to the precipitation pattern. Some of the emerging waves with an initial equatorward component pf velocity may suffer reflection at the plasmapause. It is suggested that the resultant low-latitude chorus boundary at the Ogo 6 orbit is close to the magnetic field line marking the low-altitude boundary of the plasmasphere and may be an indicator of this plasmapause position under a wide range of magnetospheric conditions.