Evolution of Radiation Belt Electron Pitch Angle Distribution Due to Combined Scattering by Plasmaspheric Hiss and Magnetosonic Waves

Abstract

Both magnetosonic (MS) waves and plasmaspheric hiss can resonantly scatter outer radiation belt electrons, leading to various electron pitch angle distribution. Based on electron diffusion coefficients calculations and 2-D Fokker-Planck diffusion simulations, we perform a parametric study to quantitatively investigate the net electron scattering effect and the relative contributions of simultaneously occurring hiss and MS waves with groups of different wave amplitude combinations. It is found that the combined scattering effects are dominated by pitch angle scattering due to hiss emissions at L = 4, when their amplitude is comparable to or stronger than that of MS waves, thereby producing the butterfly, top-hat, flat-top, and pancake pitch angle distributions, while the butterfly distributions can evolve over a broader energy range when MS waves join the combined scattering effects. Our results demonstrate that the relative intensities of various plasma waves play an essential role in controlling the radiation belt electron dynamics.