Nonlinear Evolution of Radiation Belt Electron Fluxes Interacting With Oblique Whistler Mode Chorus Emissions
Yikai Hsieh, Y. Kubota, Yoshiharu Omura
Abstract
Abstract Nonlinear whistler mode wave‐particle interaction is one of the processes to generate relativistic electrons in the Earth's outer radiation belt. Applying test particle simulations with a pair of whistler mode chorus emissions, we traced a large number of electrons in various initial conditions along an magnetic field line to build a set of Green's functions for analyzing evolution of the electron distribution under the chorus emissions. Employing convolution integral for the Green's functions, we tracked the formation of relativistic electron fluxes from an injected energetic electron through interaction with consecutive chorus emissions. We compared the simulation results among a purely parallel wave model and two oblique wave models with wave normal angles gradually increased from 0° to 20° and 60°. Multiple resonances result in a higher probability of nonlinear trapping. Hence, the trapped electrons for the oblique cases are scattered to a wider range of pitch angles than those for the parallel case. Oblique chorus can accelerate 10–30 keV electrons to MeV level rapidly in several wave emission cycles (about 10 s), which is much faster than that of the parallel wave model. The study shows comprehensive evolutions of electron fluxes interacting with oblique chorus emissions through cyclotron and Landau resonances in the outer radiation belt.