Quantitative assessment of earth's radiation belt electron acceleration

The highly dynamical evolution of the Earth's Van Allen radiation belt electron fluxes is due to competitions between various loss and acceleration processes. In this paper, we focus on analyzing an interesting event, where electrons experienced very rapid acceleration from hundreds of keV to multi-MeV within 12-16 hours in the heart of the outer radiation belt. Using 3D particle diffusion code, we simulate radiation belt electron evolution by including important physical processes, such as radial diffusion due to interaction with ultra-low-frequency waves, as well as pitch angle and energy diffusion driven by whistler-mode chorus waves. A quantitative comparison against the Van Allen Probes electron measurements clearly shows that chorus waves play a critical role in accelerating electrons to multiple MeV through producing the growing peaks in electron phase space density and the characteristic flat-top pitch angle distributions, while radial diffusion plays an important role in redistributing electrons from the developing peaks to other locations.