High‐resolution energetic particle measurements at 6.6 RE, 1. Electron micropulsations

The three papers dealing with data from satellites 1976‐059A and 1977‐007A which we present in this issue represent the first publication of data from the new series of charged particle analyzer (CPA) instruments designed to measure energetic particle fluxes at geosynchronous altitudes. This first report presents new results on electron micropulsation phenomena and includes a concise description of the instrument. We often observe highly periodic modulations which persist for times as long as 2 hours in the spin‐averaged counting rate data. These flux oscillations occur most frequently in the 30‐ to 300‐keV electron data but are occasionally seen in higher‐energy electron or low‐energy proton data. The pitch angle distributions of the observed modulated fluxes may be either ‘cigar‐shaped’ or ‘pancake‐shaped.’ Oscillations at different energies are in phase, although the gross counting rate may be changing in an energy‐time dispersive manner. The occurrence distribution of these modulations in local time suggests that they are related to Pc 5 geomagnetic micropulsations observed at ground stations.