[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-12] Observation and Numerical Simulation of Cold Ions Energized by EMIC Waves

*Khan-Hyuk Kim¹、Chae-Woo Jun²、Jong-Woo Kwon³、Junhyun Lee¹、Kazuo Shiokawa²、Yoshizumi Miyoshi²、Eun-Hwa Kim^4,5、Kyungguk Min⁶、Jungjoon Seough⁷、Kazushi Asamura⁸、Iku Shinohara⁸、Ayako Matsuoka⁹、Shoichiro Yokota¹⁰、Yoshiya Kasahara¹¹、Satoshi Kasahara¹²、Tomoaki Hori²、Kunihiro Keika¹²、Atsushi Kumamoto¹³、Fuminori Tsuchiya¹³ (1.School of Space Research, Kyung Hee University, Yongin, Gyeonggi, Republic of Korea、2.Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan、3.Division of Atmospheric Sciences, Korea Polar Research Institute, Incheon, Republic of Korea、4.Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey, USA、5.Department of Physics, Andrews University, Berrien Springs, Michigan, USA、6.Department of Astronomy and Space Science, Chungnam National University, Daejeon, Republic of Korea、7.Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea、8.ISAS/JAXA, Sagamihara, Japan、9.Kyoto University, Kyoto, Japan、10.Osaka University, Osaka, Japan、11.Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan、12.University of Tokyo, Tokyo, Japan、13.Tohoku University, Sendai, Japan)

キーワード：H-band EMIC waves , Energized cold He+ ions, Plasmatrough, Hybrid simulation

This is the first report of significant energization (up to 7000 eV) of low-energy He⁺ ions, which occurred simultaneously with H-band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He⁺ flux enhancements is mostly above 1000 eV. At some interval, the He⁺ ions are energized up to ~7000 eV. The H-band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left-handed or right-handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non-parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He⁺ energization. The simulations show that cold He⁺ ions are energized up to more than 1000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He⁺ gyrofrequency is a primary factor for transverse energization of cold He⁺ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He⁺ ions observed by Arase is attributed to H-band EMIC waves excited near the local helium gyrofrequency.