Precipitation of MeV and Sub-MeV Electrons Due to Combined Effects of EMIC and ULFWaves

摘要

We explore the mechanism of MeV and sub-MeV electron precipitations into the atmosphere in the outer radiation belt, through quasi-linear pitch-angle scattering by electromagnetic ion cyclotron (EMIC) waves, when strong compressional Pc4-Pc5 ultralow-frequency (ULF) waves are simultaneously present. Theoretically, the opposite magnetic field and density modulations produced by such ULF waves can significantly reduce the minimum electron energy for cyclotron resonance with EMIC waves, and this could potentially lead to the loss of lower energy (MeV and sub-MeV) electrons. Statistical satellite observations of simultaneous, intense EMIC and ULF waves reveal the parameter domains most conducive to such lower energy electron losses, which are shown to be mostly located near the geosynchronous orbit. Selected events further suggest that such a mechanism could be efficient in the outer radiation belt and that even larger effects might occur during strong injections from the plasma sheet.