Masafumi Shoji,Yoshizumi Miyoshi(Nagoya University)
In the Earth’s inner magnetosphere, electromagnetic plasma waves are thought to be responsible for energy exchange between charged particles in space plasmas. Especially, electromagnetic ion cyclotron (EMIC) waves affect to the wide energy range of ions and relativistic electrons. Such an energy exchange process is evidenced by phase space holes identified in the ion distribution function and measurements of the dot product of the plasma wave electric field and the ion velocity. We developed a method to detect the interactions directly by the THEMIS spacecraft data. In this study, we focused on the interactions between the EMIC waves and the energetic ions. Calculating the phase difference between the wave electromagnetic fields and particle velocities, we obtain the distribution of the ions in the phase angle, and the values indicating the nonlinear resonant currents. We showed the evidence of the nonlinear energy transfer from the energetic ions to the EMIC waves with the rising frequency. Using this method, we identify ion-holes in the distribution function and the resulting nonlinear EMIC wave evolution. This ion holes are key to wave growth and frequency drift by the ion currents through nonlinear wave particle interactions, which are identified by a computer simulation in this study.
hoji, M., Y. Miyoshi, Y. Katoh, K. Keika, V. Angelopoulos, S.
Kasahara, K. Asamura, S. Nakamura, and Y. Omura,Ion hole formation and
nonlinear generation of Electromagnetic Ion Cyclotron waves: THEMIS
observations, Geophys. Res. Lett., 44, 8730-8738,