Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events

We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17-18 March 2013 and non-storm time of 19-20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17-18 March 2013, the SYM-H minimum reached -130nT, intense chorus waves (peak B-w similar to 140pT) occurred at 3.5<L<5.5, and several hundred keV to several MeV electron fluxes increased by similar to 2 orders of magnitude mostly at 3.5<L<5.5. During 19-20 September 2013, the SYM-H remained higher than -30nT, modestly intense chorus waves (peak B-w similar to 80pT) occurred at L>5.5, and electron fluxes at energies up to 3MeV increased by a factor of similar to 5 at L>5.5. The two electron flux enhancement events were simulated using the available wave distribution and diffusion coefficients from the GEM focus group Quantitative Assessment of Radiation Belt Modeling. By comparing the individual roles of local electron heating and radial transport, our simulation indicates that resonant interaction with chorus waves is the dominant process that accounts for the electron flux enhancement during the storm time event particularly near the flux peak locations, while radial diffusion by ultralow-frequency waves plays a dominant role in the enhancement during the non-storm time event. Incorporation of both processes reasonably reproduces the observed location and magnitude of electron flux enhancement.