Formation processes of radiation belt electron fluxes interacting with localized oblique whistler mode chorus emissions

Abstract:

Generation process of energetic electrons in the Earth’s radiation belt is an unsolved problem. Whistler mode wave is believed to be a factor that accelerates electrons from energies keV to MeV through nonlinear wave-particle interactions. Oblique whistler mode waves are observed frequently in dayside and dawnside of the Earth’s magnetosphere around the outer radiation belt. We perform electron accelerations and pitch angle scatterings of wave-particle interactions between lower-band oblique whistler mode chorus emissions and electrons in this study. Electron acceleration in velocity perpendicular to the background magnetic field of resonant electrons plays an important role in both cyclotron and Landau resonances. We utilized Green’s function method to demonstrate the nonlinear wave-particle interactions.

We build up Green’s functions for a large number of electrons interacting oblique whistler mode chorus emissions. The formation processes of the outer radiation belt electron fluxes interacting with consecutive chorus emissions are traced by applying the convolution integrals for the Green’s functions. We trace the evolution of the radiation belt electron fluxes for a few minutes and find that MeV electrons are generated promptly due to the combination of cyclotron resonance and Landau resonance of wave-particle interactions. We compare the formation processes among 3 different wave models: (1) purely parallel waves; (2) gradually increasing wave normal angles from 0 degree to 20 degrees; and (3) gradually increasing wave normal angles from 0 degree to 60 degrees. The results show that case 3 can accelerate 10-30 keV electrons to MeV faster than the others. We further trace the formation processes of MeV electron fluxes for oblique chorus emissions localized in longitude for an hour, and then compare the results among several different longitudinal ranges. The acceleration rate of electrons is highly related to the longitudinal range of chorus occurrence.