Simulating the Earth's Outer Radiation Belt Electron Fluxes and Their Upper Limit: A Unified Physics-Based Model Driven by the AL Index

Abstract

Using particle and wave measurements from the Van Allen Probes, a 2-D Fokker-Planck simulation model driven by the time-integrated auroral index (AL) value is developed. Simulations for a large sample of 186 storm-time events are conducted, demonstrating that the AL-driven model can reproduce flux enhancement of the MeV electrons. More importantly, the relativistic electron flux enhancement is determined by the sustained strong substorm activity. Enhanced substorm activity results in increased chorus wave intensity and reduced background electron density, which creates the required condition for local electron acceleration by chorus waves to MeV energies. The appearance of higher energy electrons in radiation belts requires a higher level of cumulative AL activity after the storm commencement, which acts as a type of switch, turning on progressively higher energies for longer and more intense substorms, at critical thresholds.