[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P16] Direct Measurement of Pitch Angle Scattering in EMIC-Proton Interactions by the WPIA method

*竹内 亘平¹、三好 由純¹、浅村 和史²、寺澤 賢哉¹、Jun Chae-Woo¹、笠原 禎也³、笠羽 康正⁴、松田 昇也³、土屋 史紀⁴、熊本 篤志⁴、堀 智昭¹、新堀 淳樹¹、松岡 彩子⁵、寺本 万里子⁶、山本 和弘¹、篠原 育²、北村 成寿¹ (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　宇宙科学研究所、3.金沢大学、4.東北大学、5.京都大学、6.九州工業大学)

Electromagnetic ion cyclotron waves (EMIC), a type of plasma waves, are known to exchange energy with ions through a process called wave-particle interaction. This interaction is supposed to contribute to the acceleration and scattering of ions in the magnetosphere. The Wave-Particle Interaction Analysis (WPIA) is a method that enables direct and quantitative measurement of such interactions. By applying WPIA to observational data from the Arase satellite, Shoji et al. (2017, 2021) successfully demonstrated the direct detection of energy transfer between EMIC waves and ions, as well as frequency variations in EMIC waves. However, direct observations of the Lorentz force, which is responsible for pitch-angle scattering, remains. In this study, we applied the WPIA method to the Arase satellite observations to directly detect the pitch angle changes caused by the Lorentz force. We analyzed an event on October 27, 2022, when the Arase satellite observed intense proton-band EMIC waves associated with pitch angle scattering.
By calculating V×B, which represents change of pitch angle, and V・E, which represents energy exchange between protons and EMIC waves, we successfully detected proton energy loss. Simultaneously, we found that the Lorentz force induced by the plasma waves caused pitch angle changes toward the loss cone.