Particle simulations of whistler-mode rising-tone emissions triggered by waves with different amplitudes

Abstract

We perform self-consistent electromagnetic particle simulations to analyze whistler-mode triggered emissions in the magnetosphere. The whistler-mode triggering waves with different wave amplitudes and a constant frequency are injected at the equator. With triggering wave amplitudes greater than the threshold for the nonlinear wave growth, rising-tone emissions are successfully excited near the equator. The detailed time evolutions of amplitudes and frequencies of the rising-tone emissions show similar development. A recent theoretical study found the optimum amplitude of triggering waves for rising-tone emissions. The optimum amplitude condition is confirmed by the simulations. A triggering wave with an amplitude much greater than the optimum amplitude cannot trigger a rising emission. In a process where triggered emissions develop, phase-organized resonant electrons clearly appear in the velocity-phase space, contributing to the nonlinear wave growth. The simulation study shows that amplitudes and frequency sweep rates of triggered emissions do not depend on the amplitude of a triggering wave.