RELATIVISTIC (E> 0.6, > 2.0, AND > 4.0 MeV) ELECTRON ACCELERATION AT GEOSYNCHRONOUS ORBIT DURING HIGH-INTENSITY, LONG-DURATION, CONTINUOUS AE ACTIVITY (HILDCAA) EVENTS

Abstract

Radiation-belt relativistic (E > 0.6, > 2.0, and > 4.0?MeV) electron acceleration is studied for solar cycle 23 (1995-2008). High-intensity, long-duration, continuous AE activity (HILDCAA) events are considered as the basis of the analyses. All of the 35 HILDCAA events under study were found to be characterized by flux enhancements of magnetospheric relativistic electrons of all three energies compared to the pre-event flux levels. For the E > 2.0?MeV electron fluxes, enhancement of >50% occurred during 100% of HILDCAAs. Cluster-4 passes were examined for electromagnetic chorus waves in the 5 0.6, > 2.0, and > 4.0?MeV electrons occurred ~1.0?day, ~1.5?days, and ~2.5?days after the statistical HILDCAA onset, respectively. The statistical acceleration rates for the three energy ranges were ~1.8?? 105, 2.2?? 103, and 1.0?? 101 cm?2 s?1 sr?1 d?1, respectively. The relativistic electron-decay timescales were determined to be ~7.7, 5.5, and 4.0?days for the three energy ranges, respectively. The HILDCAAs were divided into short-duration (D ? 3?days) and long-duration (D > 3?days) events to study the dependence of relativistic electron variation on HILDCAA duration. For long-duration events, the flux enhancements during HILDCAAs with respect to pre-event fluxes were ~290%, 520%, and 82% for E > 0.6, > 2.0, and > 4.0?MeV electrons, respectively. The enhancements were ~250%, 400%, and 27% respectively, for short-duration events. The results are discussed with respect to the current understanding of radiation-belt dynamics.