Parametric Dependence of Polarization Reversal Effects on the Particle Pitch Angle Scattering by EMIC Waves

Abstract

AbstractElectromagnetic ion cyclotron (EMIC) waves play an important role in the loss of radiation belt electrons and ring current protons. After EMIC waves are excited near the magnetic equator, they will propagate to high latitudes and suffer a polarization reversal from left‐handed to right‐handed polarized at the crossover frequency. To improve the current understanding of the EMIC wave‐induced loss of radiation belt electrons and ring current protons, we perform a detailed analysis of the sensitivity of polarization reversal effects to L‐shell, electron number density, and wave frequency spectrum. Our results show that polarization reversal contributes significantly to the pitch angle diffusion coefficients at low pitch angles extending to the loss cone angle for various parameter sets. Compared with the diffusion coefficients only using L‐mode dispersion relation, inclusion of polarization reversal mainly enhances the electron scattering loss at several MeV and weaken the proton scattering loss over a broad energy range from a few keV to 1 MeV. While the increase of electron diffusion coefficients can be up to a factor of 5, the decrease of proton diffusion coefficients can be larger than an order of magnitude. As L‐shell or electron density increases, the affected resonant region by polarization reversal for both electrons and protons tends to expand to lower energies, while an increase of peak wave frequency will shift the resonant region to higher energies. Our results confirm the vital importance of including polarization reversal in understanding the EMIC wave‐induced scattering loss of radiation belt electrons and ring current protons.