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

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.