Temporal evolution of relativistic electrons induced by fast magnetosonic waves in the radiation belts

We study the influence of fast magnetosonic ( MS) waves on the temporal evolution of the phase space density (PSD) of relativistic electrons in the outer radiation belts. We evaluate the bounce-averaged pitch angle, momentum and cross-diffusion rates, and find that all the diffusion rates are most pronounced within a limited region of pitch angles: similar to 50 degrees-70 degrees. Consequently, numerical solutions of a 2D momentum-pitch angle diffusion equation show that significant increases in electron PSDs at energies of 1 MeV or above occur primarily within such a limited region of pitch angles. Moreover, neglecting cross-diffusion rates generally produces relatively large overestimates in the PSD evolution. The current results suggest that MS waves are primarily responsible for acceleration of relativistic (>1 MeV) electrons around relatively high pitch angles.