Energetic Electron Precipitation Induced by Oblique Whistler Mode Chorus Emissions

Abstract

AbstractEnergetic electron acceleration and precipitation in the Earth's outer radiation belt are highly associated with wave‐particle interactions between whistler mode chorus waves and electrons. We perform test particle simulations to investigate electrons interacting with parallel and oblique chorus emissions with maximum amplitude 2.1 nT and 370 pT at L = 4.5. We build up a database of Green's functions, which are treated as results of the input electrons interacting with one chorus emission. The loss process of electrons caused by consecutive chorus emissions in the outer radiation belt are traced by applying the convolution integrals of distribution functions and the Green's functions. Oblique chorus emissions lead to more electron precipitation than parallel chorus emissions in the range 370 pT–2.1 nT. By checking the resonance condition and resonant energies, we find that electrons are difficult to be scattered into the loss cone directly by Landau resonance. We propose a two‐step precipitation process for oblique chorus emissions that contributes to more electron loss: (a) Through Landau resonance interaction with a chorus emission, electrons at high pitch angles are effectively accelerated in the parallel direction, and their pitch angles become lower. (b) The electrons bounce back toward the equator, and they are pushed into loss cone through nonlinear scattering due to cyclotron resonance with another chorus emission. The combination of Landau resonance and cyclotron resonance by oblique chorus emissions results in a higher precipitation rate than the single cyclotron resonance by purely parallel chorus emissions.