Oral Presentation

On the Generation and Expansion of the Chorus Waves Observed After the Injection of Electrons at the Onset of a Substorm

Author(s): Ling-Hsiao Lyu and Yu-Chun Huang (Institute of Space Science and Engineering, National Central University)

Presenter: Ling-Hsiao Lyu (National Central University)

In this study, we show a possible mechanism that can explain the observed quasi-periodic broad-band emissions of whistler-chorus waves after the injection of electrons at the onset of a substorm. It is found that the injected electrons will gain significant kinetic energy from the convection electric field when they drift toward the dawn side due to the grad-B drift and the curvature drift. The mirror points will move toward the magnetic equator when the electrons move toward the inner L-shell. The gyro motion and the bounce motion of these energetic electrons can emit broad-band backscattering waves with frequencies below the electrons’ gyrofrequency. Namely, for an observer located beyond the mirror points can observe the sub-electron-gyrofrequency chorus waves during half cycle of the electrons’ bounce motion. The expansions of the localized chorus waves are studied based on the group velocity distribution of the chorus waves. Our results show that the group velocity distribution of the chorus waves can naturally explain the frequency gap at half of the electrons’ gyrofrequency.