SAMPEX observations of precipitation bursts in the outer radiation belt

The occurrence frequency of precipitation bursts of > 1 MeV electrons in th e outer radiation belt is examined using data from the SAMPEX satellite. El ectron burst characteristics shown in this paper include the dependence of the precipitation on magnetic local time, radial distance and geomagnetic a ctivity. Precipitation bursts with timescales <1 s, i.e., microbursts, are studied in detail, including their dependence on the phases of geomagnetic storms. It is found that precipitation bursts occur typically in the region between L = 4 and L = 6. Microbursts tend to occur at L Bower than the bur s ts with timescales of several tens of seconds. The number of observed mic robursts significantly increases during storms, appearing mainly in the mor ning sector early in the recovery phase of storms. These findings suggest t hat the microbursts may be due to interactions with electron whistler waves , which take place near the dawnside plasmapause in the density irregularit ies that are perhaps created in the "recovering" plasmasphere. The prevalen ce of bursty precipitation indicates that this enhanced loss component of t he relativistic electron flux should be taken into account in any quantitat ive model of relativistic electron acceleration processes.