Long-Term Radiation Belt Electron Dynamics Driven by Chorus Waves

Debates have been lasting for decades on how to characterize resonant interactions between magnetospheric electrons and plasma waves. Practically, quasilinear theory is applied to model the evolution of electron populations. Under this framework, electron dynamics are approximated as diffusion processes described by Fokker-Planck equation, which are governed by the time-averaged wave power spectrum only. For wave modes such as chorus, fine structures including discreteness and frequency chirping are left out. These structures, together with the intense, coherent nature of chorus waves, could possibly induce nonlinear electron motions which are rapid in phase space. Quantifying the deviation from quasilinear theory is important for accurate space weather forecasts.

Self-consistent PIC simulations can generate chorus waves with all key features realistic. By performing test-particle simulations with PIC-originated chorus waves, we track an ensemble of electrons for several bounce periods to make detailed comparisons between the evolution of its distribution function and quasilinear theory. Varying L-shell and wave packet spacings in PIC simulations shows the sensitivity of our results.