Rapid precipitation of radiation belt electrons induced by EMIC rising-tone emissions localized in longitude inside and outside the plasmapuase

We perform test particle simulations for four different cases with proton-band or helium-band EMIC waves occurring outside or inside the plasmapause, respectively developing wave models based on the nonlinear wave growth theory [Omura et al., JGR, 2010; Shoji and Omura, JGR, 2013]. Assuming a pair of EMIC rising-tone emissions occurring at the equator and propagating northward and southward in a region localized in longitude, we study their effects on a whole radiation belt electron distribution all around the Earth. The electrons drift eastward in the dipole magnetic field, and some of them encounter the localized waves. In the wave generation region, we monitor fluxes of electrons being lost into the atmosphere. Nonlinear wave potentials generated by coherent EMIC rising-tone emissions trap a fraction of resonant electrons, resulting in efficient scattering to lower pitch angles [Omura and Zhao, JGR, 2012, 2013; Kubota et al., JGR, 2015]. Through the nonlinear wave trapping alone, however, we note that electrons scattered in pitch angle cannot enter into the loss cone. Based on theoretical and numerical analyses, we find that the electrons are precipitated into the atmosphere rapidly not only by the nonlinear wave trapping but also by another nonlinear scattering named SLPA (Scattering at Low Pitch Angle). The efficiency of electron precipitation as a function of kinetic energy varies significantly depending on the wave frequency range and the plasma density. In the time evolution of an electron distribution observed locally in longitude, we also find echoes of electron depletion by the localized EMIC emissions.