Multipoint Measurements of Energetic Particle Deep Penetration into the Low L Region

Abstract:

Energetic electrons in the inner magnetosphere are distributed into two regions: the inner radiation belt and the outer radiation belt, while the slot region in between separating the two belts. The deep penetration of energetic electrons into the slot region and inner belt is thought to be a major source process of inner belt electrons and thus has attracted a lot of attention. Energetic particle measurements from the Van Allen Probes revealed significant differences of deep penetration into L<4 of energetic particles with different energies and/or species. The deep penetrations of tens to hundreds of keV electrons into low L region occur frequently and the penetration frequency and depth are energy dependent, while deep penetrations of MeV electrons and hundreds of keV ions are much rarer; and MLT dependent deep penetration has also been observed. In this study, focusing on multiple events, we use multipoint measurements of energetic particle deep penetration to understand the systematic differences in differential deep penetrations of energetic particles of different energies and species, and the results help us gain more insight into the underlying physical processes. Simultaneous in situ observations at same L shells but different magnetic local times during deep penetration events are shown and detailed energy spectra and pitch angle distributions are investigated. Timing and MLT dependence of deep penetrations are also revealed and the underlying physical processes are discussed. The multipoint measurements shed lights on the physical processes responsible for the energetic particle penetration into the low L region.