Electron source associated with dipolarization at the outer boundary of the radiation belts: Non‐storm cases

Abstract

We examine the strength of the electron source associated with dipolarization at the outer boundary of the radiation belts using multisatellite observations from THEMIS. This topic is relevant to the determination on the relative roles of inward radial diffusion versus internal local acceleration for the origin of the relativistic electrons in the outer radiation belt. We focus on the electron phase space density (PSD) as a function of the first adiabatic invariant (μ) for equatorially mirroring population over a broad energy range. It is found that the source strength associated with dipolarization for non‐storm periods at the outer boundary of the radiation belts can be well above the observed fluxes of relativistic electrons inside the outer radiation belt. The PSD change due to the magnetic field strength variation dominates over PSD change from the energy flux increase with dipolarization, resulting in a strong anticorrelation between magnetic field strength and PSD values at a given μ. If observations from closely spaced satellites during the same event can be used to indicate radial transport of electrons with dipolarization, then the observed PSD at these satellites indicates frequent occurrence of non‐adiabatic process during their radial transport.