Observations of energetic electrons at synchronous altitude: 1. General features and diurnal variations

Energetic electron fluxes above four integral thresholds (Ee > 300 kev, >450 kev, 1.05 Mev, and 1.9 Mev) were measured at synchronous altitude (R = 6.6 RE) during the first half of 1967 on board the ATS 1, satellite (1966–110A). The fluxes show a diurnal variation with the noon-to-midnight ratio being larger for the more energetic electron groups and being larger, on the average, for magnetically disturbed days. Magnetic storms produce a great deal of fine structure in the electron fluxes, with changes occurring on the time scale of minutes; the effect of such storms is to depress the fluxes. Recovery to prestorm level is an energy-dependent process that proceeds more slowly for more energetic electrons and apparently in a stepwise manner.