Particle-in-Cell Simulation of Rising-Tone Magnetosonic Waves

Recent observations have reported that magnetosonic waves can exhibit rising-tone structures in the frequency-time spectrogram. However, the generation mechanism has not been identified yet. In this paper, we investigate the generation of rising-tone magnetosonic waves in the terrestrial magnetosphere using 1-D particle-in-cell (PIC) simulations, in which the plasma consists of three components: cool electrons, cool protons and ring distribution protons. We find that the magnetosonic waves excited by the ring distribution protons can form a rising-tone structure with frequency of the structure ranging from about0.5 Omega(lh) to nearly Omega(lh), where Omega(lh) is the lower hybrid frequency. It is further demonstrated that the rising frequency of magnetosonic waves can be accounted for by the scattering of ring distribution protons. Moreover, the rising-tone timescale obtained by PIC simulation is compared with the satellite observation. Our findings provide some new insights to understand the nonlinear evolution of plasma waves in the Earth's magnetosphere.