Particle substorms observed at the geostationary orbit

A correlation study of the sudden intensity increases seen in the 50–150 kev and 150–500 kev energy channels of the ATS 1 electron spectrometer with the occurrence of magnetic substorms recorded at midnight has been made. As a result of this study, the following conclusions applicable for times of moderate magnetic activity are arrived at: (1) Electrons are produced in the 50–150 kev energy range as observed at 6.6 RE during a magnetic substorm. The spectrum is soft since electrons are not always observable in the second energy window. (2) The electrons are produced at or near the midnight meridian and then drift on closed field lines around the earth. (3) The electron bunch produced as a result of the substorm in 75% of the 60 events studied is associated with precipitation observed by riometers as it drifts. An apparent dependence of precipitation on the level of substorm activity as given by the AE index suggests that the electrons are often produced of sufficient intensity to exceed a stable upper limit for trapped electrons at 6.6 RE. (4) The frequency of occurrence of such particle substorms indicates that they might represent a quasi-steady source of electrons for the trapped radiation.