On the Energy‐Dependent Deep (L < 3.5) Penetration of Radiation Belt Electrons

Abstract

Energetic electrons in the inner magnetosphere are normally trapped in two regions: the inner and outer radiation belts. The inner belt is relatively stable, while the outer belt is highly dynamic, with electron fluxes varying by orders of magnitude within days during geomagnetic storms. The slot region, usually devoid of energetic electrons, separates the two belts. During geomagnetically active times, outer belt electrons can extend to lower L (distance to the center of Earth in units of Earth radii in the equatorial plane) and even fill the slot region (Blake et al., 1992;Li et al., 1993). The dynamic variations of radiation belt particles are the result of a complex competition between acceleration, transport, and loss mechanisms. The most important source process for inner belt electrons is inward radial transport from the outer belt (Cunningham et al., 2018;Selesnick, 2016) with cosmic ray albedo neutron decay (CRAND) contributing at the inner edge of the inner belt (Li et al., 2017;Xiang et al., 2019;Zhang et al., 2019). The energy-dependence of outer belt electrons penetrating inward can help quantify the populations of electrons transported to the inner belt during a certain event, which is important for determining source and loss processes of inner electrons. This study will focus on the mechanism responsible for the energy-dependent penetration of outer belt electrons into the low L region (L < 3.5). Our study provides