Relativistic electron precipitation due to nonlinear pitch-angle scattering by EMIC triggered emissions

We show that the anomalous cyclotron resonance between relativistic electrons and EMIC triggered emissions [1,2] takes place very effectively near the magnetic equator because of the rising-tone frequency and the variation of the ambient magnetic field. Efficient precipitations are caused by nonlinear trapping of relativistic electrons by electromagnetic wave potentials formed by EMIC triggered emissions. Frequency sweep rates of rising-tone emissions and the inhomogeneous magnetic field play essential roles in the nonlinear trapping of resonant electrons, transferring them to lower pitch angles [3]. We derive the necessary conditions of the wave amplitude, kinetic energies, and pitch angles that must be satisfied for the nonlinear wave trapping. We have conducted test particle simulations with a large number of relativistic electrons undergoing mirror motion in a parabolic magnetic field near the magnetic equator [4]. In the presence of coherent EMIC triggered emissions with increasing frequencies, a substantial amount of relativistic electrons is trapped by the wave, and the relativistic electrons at high pitch angles are guided to lower pitch angles within a short time scale much less than a second, resulting in rapid precipitation of relativistic electrons or relativistic electron microbursts.