Modeling advective transport of radiation belt electrons

Abstract

The relativistic electron dynamics in the radiation belts falls into two categories: diffusive processes, in which particles are scattered randomly, and advective processes, in which particles are collectively driven in one direction in energy or space. In this work, we focus on advection which can occur on a timescale faster than diffusion for CME shock compressions of the dayside magnetosphere. Test-particle simulations are done in the electric and magnetic fields generated by the LFM global MHD model, and the advection coefficient is calculated. Then, the advection coefficient is applied to the transport equation with advection term included and solved for phase space density time evolution. The calculation is done for 17 March 2015 and 6–7 September 2017 CME-shock events, using realistic initial conditions measured by Van Allen Probes, all showing inward motion of electrons on the time scale of minutes. The result is compared with the phase space density calculated based on full test-particle simulations in MHD fields. The inward shift in phase space density is found to be comparable for both methods, while solving the transport equation is much faster once advection coefficients are modeled.