Roles of Radial Diffusion and Chorus-driven Diffusion in the Outer Belt Relativistic Electron Acceleration During the Non-Storm Period of 13–15 January 2013

The acceleration mechanisms of relativistic electrons in the outer radiation belt have been widely investigated during geomagnetic storms. However, non-storm time acceleration of relativistic electrons attracts less attention and its underlying mechanism has yet well understood. Here we investigate a rapid acceleration event for > ~MeV relativistic electron at L* > 5 after moderate substorm during the non-storm period of 13-15 January, 2013. To clarify the roles of potential physical mechanisms, a 3D numerical simulation including two typical radial diffusion models and event-specific chorus waves is conducted. The simulation results are further compared with Van Allen Prboe observations. The comparison shows that the dominant mechanism for the relativistic electron acceleration during this non-storm event exhibit clear energy-dependence. Specifically, radial diffusion plays a dominant role in ~MeV electron acceleration whereas local diffusion driven by chorus waves primarily accelerate ~2 MeV electrons. In addition, the combination of both mechanisms facilitates the acceleration process more effectively than either alone and can well capture the enhanced magnitude of electron phase space densities, thus underscoring a robust cooperative role in relativistic electron acceleration. Our results suggest the competition and incorporation of radial diffusion and local acceleration driven by chorus in relativistic electron acceleration. Our study advances the understanding of relativistic electron acceleration mechanisms during non-storm periods, providing insights for optimizing radiation belt modeling and prediction.