A study of the plasma wave enhancements in the Earth’s equatorial plasmasphere using the resonance conditions

To improve our understanding of the mechanism generating plasma waves from instabilities, a comparison of observations and linear growth-rate calculations is presented. We use the initial parameters inferred from observational data obtained around the plasma-wave generation region obtained by the Akebono satellite. The linear growth rates of waves of different modes are calculated under cyclotron interaction process conditions, and compared with simulation results and observations. By employing numerical experiments, we first show that upper hybrid-, Z-, and whistler-mode waves are excited through instabilities driven by a ring-type velocity distribution. The results suggest a possibility that energetic electrons with energies of some tens of keV confined around the geomagnetic equator are responsible for the observed enhancements of Z- and whistler-mode waves.