Resonance broadening effect for relativistic electron interaction with electromagnetic ion cyclotron waves

Relativistic electron scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms for > 1 MeV electron flux depletion in the Earth's radiation belts. Resonant electron interaction with EMIC waves is traditionally described by quasi-linear diffusion equations, although spacecraft observations often report EMIC waves with intensities sufficiently large to trigger nonlinear resonant interaction with electrons. An important consequence of such nonlinear interaction is the resonance broadening effect due to high wave amplitudes. In this study, we quantify this resonance broadening effect in electron pitch-angle diffusion rates. We show that resonance broadening can significantly increase the pitch-angle range of EMIC-scattered electrons. This increase is especially important for & SIM; 1 MeV electrons, where, without the resonance broadening, only those near the loss cone (with low fluxes) can resonate with EMIC waves. Published under an exclusive license by AIP Publishing.