Modeling of relativistic electron precipitation into the atmosphere by Electromagnetic Ion Cyclotron Waves

Abstract:

Radiation belt electron loss (dropout) during storm main phase is a long-standing scientific question. One of potential loss mechanisms is resonant scattering due to electromagnetic ion cyclotron (EMIC) waves. We will first review the observation and models of EMIC waves in the magnetosphere, especially EMIC wave storm-time dependence. Then the dynamics of relativistic electrons traveling through a parallel-propagating EMIC wave in the Earth's dipole field are modeled via test particle simulations. For the first time, both resonant and nonresonant scattering in pitch angle are considered. Resonant electrons tend to experience nonlinear phase bunching, leading to advection towards larger pitch angles and thus impeding loss into the atmosphere. On the other hand, nonresonant electrons, with energies below the minimum resonant energy down to 100's of keV, are scattered stochastically in pitch angle and can be scattered into the atmospheric loss cone at a rate comparable to strong diffusion limit for wave amplitudes above 2 nT. This nonresonant effect, which is excluded from current quasi-linear theory, can be an efficient loss mechanism of relativistic electrons in the radiation belts.