Global distributions of suprathermal electrons observed on THEMIS and potential mechanisms for access into the plasmasphere

Abstract

Statistical results on the global distribution of suprathermal electron (0.1–10 keV) fluxes are shown both outside and inside the plasmasphere separately, using electron data from THEMIS. Significant electron fluxes are found within the plasmasphere, although they are nevertheless smaller than the populations outside the plasmasphere. Electron fluxes outside of the plasmapause increase with stronger magnetic activity on the nightside and decrease as a function of increasing magnetic local time (MLT). Inside the plasmasphere, electron fluxes increase just inside of the plasmapause, particularly from the midnight to the dawn sector during active times, while electron distributions are less MLT‐dependent during quiet times. Inside the plasmasphere, electron fluxes are larger and more stable at smaller L shells at higher energy (a few to 10 keV), while electron fluxes decrease at smaller L shells at lower energy (less than a few keV). Our new statistical results on the suprathermal electron distribution both inside and outside the plasmasphere provide essential information for the evaluation of wave propagation characteristics. Case analyses have been performed in order to understand potential mechanisms responsible for electron access into the plasmasphere. The first case analysis shows that during a relatively quiet time following a disturbed interval, deeply injected suprathermal electrons remain trapped at low L shells during the refilling of the plasmasphere and eventually form the plasmaspheric population. The second case analysis suggests that a combination of locally enhanced electric field and subsequent energy‐dependent azimuthal magnetic drift may be able to trap the suprathermal electrons inside the plasmasphere during a geomagnetically active period.