Satellite observations of impulsive Bremsstrahlung X ray events associated with substorms

With bremsstrahlung X ray data taken on a polar‐orbiting satellite a study has been made of impulsive electron (>50 keV) precipitation events at high latitudes, many of which occurred in the vicinity of local midnight near the beginning of a magnetic substorm. The impulsive events were truly temporal in character and lasted for times of the order of 5 min or less. The angular distributions of the X rays measured at the satellite indicated that the electron precipitation occurred generally near the energetic electron (>155 keV) trapping boundary with a tendency often to be somewhat poleward of that boundary. Just prior to the onset of several of the events there was a significant decrease in X ray flux. The energy spectra often softened during the pronounced increases in X ray flux. For some of the events the maximum total rate of precipitation of electrons of >50 keV into the atmosphere was ∼1023 particles/s over the broad region of observation spanning a MLT range of about 6 hours near the midnight sector. The total energy dissipation rates by electrons of >50 keV over the same MLT interval were found to be in the range from 2.5 × 1014 to 2.8 × 1016 ergs/s.