Drift mirror instability in the magnetosphere: Particle and field oscillations and electron heating

The published L = 5 equatorial magnetosphere particle and field data from the April 18, 1965, geomagnetic storm are reanalyzed in the context of the drift mirror instability theory developed by Hasegawa. These data, together with previously unpublished electron pitch-angle data, are shown to satisfy the requirements and consequences of the instability. Additional particle data observed during a 1967 substorm by an experiment on ATS 1 are also presented to show that the observation of the April 18 instability was not an isolated occurrence in the magnetosphere. The data also contain evidence for electron heating during the time of the instability.