Nonlinear spatiotemporal evolution of whistler mode chorus waves in Earth's inner magnetosphere

Abstract

We analyze the nonlinear evolution of whistler mode chorus waves propagating along a magnetic field line from their equatorial source. We solve wave evolution equations off the equator for the wave magnetic field amplitude and wave frequency, subject to boundary conditions at the equator comprising model "chorus equations" that describe the generation of a seed chorus element. The electron distribution function is assumed to evolve adiabatically along a field line. The wave profiles exhibit nonlinear convective growth followed by saturation. Convective growth is due to nonlinear wave trapping, and the saturation process is partly due to a combination of adiabatic effects and a decreasing resonant current with latitude. Notwithstanding computationally expensive full-scale kinetic simulations, our study appears to be the first to analyze the nonlinear evolution and saturation of whistler mode waves off the equator.