Auroral-zone electron precipitation accompanying a sudden impulse in the geomagnetic field

The precipitation of electrons on the auroral zone has been observed with various forms of geomagnetic activity: positive and negative bays, giant and micropulsations, as well as the sudden commencement of geomagnetic storms. Under these conditions as well as others of relative magnetic quiet, the electron influx displays various types of time variations, most readily observed through bremsstrahlung reaching balloon altitudes. The range of these temporal features extends from microbursts [Anderson and Milton, 1964] of less than 1-second duration to pulsations [Barcus et al., 1966] with intervals between consecutive peaks from 5 to 15 seconds and beyond to long-period pulsations [Anger et al., 1963] where the time scale reaches up to several hundred seconds between peaks. All of these variations were identified after the observation of electron precipitation at the sudden commencement of magnetic storms [cf., e.g. Brown, 1966]. In addition, the earlier SC observations were made either with instruments or in conditions where little time resolution was possible.