[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P06] Direct detection of proton pitch angle scattering by EMIC waves: Arase observations

*Kenya Terasawa¹, Masafumi Shoji¹, Yoshizumi Miyoshi¹, Satoko Nakamura¹, Kazushi Asamura², Yasumasa Kasaba³, Satoshi Kasahara⁴, Ayako Matsuoka⁵, Iku Shinohara⁶ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.Planetary Plasma and Atmospheric Research Center, Tohoku University, 4.The university of Tokyo, 5.Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, 6.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science)

Energy exchange between charged particles and electromagnetic ion cyclotron waves (EMIC waves) have been supposed to contribute acceleration and scattering of ions in the magnetosphere.It has been suggested theoretically that when energy is transferred from ions to EMIC waves, the pitch angle of ions decreases and ions precipitate into the Earth's ionosphere. It was difficult for conventional observations to measure changes of pitch angle and energy through wave-particle interaction. We have developed the WPIA method that can directly calculate the phase differences between the velocity vector of gyrating ions and electric/magnetic fields of EMIC waves, and the method successfully detected energy exchange between EMIC waves and ions associated with rising tone (Shoji+, 2017) and falling tone (Shoji+, 2021). However, there have been no studies about the pitch angle scattering of protons by EMIC waves with the WPIA methods. On June 21, 2021, the Arase satellite successfully observed intense EMIC waves by PWE/EFD and MGF and deformation of the pitch angle distribution of ions by LEPi simultaneously. For this event, we applied the WPIA analysis and calculated v x B as well as v・E. The results show that significant Lorentz force works to decrease pitch angles of ions. At the same time, several protons increase their energy with increasing their pitch angles. These are the first direct evidence of the pitch angle scattering between EMIC waves and ions in the space plasma. In this presentation, we discuss what parameters contribute to the saturation and decay of EMIC wave amplitudes.