[P-EM13] Dynamics of the Inner Magnetospheric System

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

*寺澤 賢哉¹、小路 真史¹、三好 由純¹、中村 紗都子¹、浅村 和史²、笠羽 康正³、笠原 慧⁴、松岡 彩子⁵、篠原 育⁶ (1.名古屋大学宇宙地球環境研究所、2.宇宙航空研究開発機構宇宙科学研究本部、3.東北大学 惑星プラズマ・大気研究センター、4.東京大学、5.京都大学 理学研究科 地磁気世界資料解析センター、6.宇宙航空研究開発機構／宇宙科学研究所 )

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.