[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P28] Precipitation of high-energy electrons into the mesosphere associated with pulsating aurorae: Arase and EISCAT conjugate observations

*Yuya Obayashi¹, Yoshizumi Miyoshi¹, Kazuteru Takahashi¹, Keisuke Hosokawa², Yasunobu Ogawa³, Shinji Saito⁴, Shin-ichiro Oyama¹, Kazushi Asamura⁵, Yoichi Kazama⁶, Shiang-Yu Wang⁶, Satoshi Kasahara⁷, Shoichiro Yokota⁸, Takefumi Mitani⁵, Takeshi Takashima⁵, Iku Shinohara⁵, Chae-Woo Jun¹, Tomoaki Hori¹, Kunihiro Keika⁷, Yoshiya Kasahara⁹, Shoya Matsuda⁹, Fuminori Tsuchiya¹⁰, Atsushi Kumamoto¹⁰, Satoko Nakamura¹, Ayako Matsuoka¹¹, Kero Antti¹², Pekka Verronen^12,13, Esa Turunen¹² (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.University of Electro-Communications, 3.National Institute of Polar Research, 4.National Institute of Information and Communication Technology, 5.ISAS, JAXA, 6.Academia Sinica, Taiwan, 7.The University of Tokyo, 8.Osaka University, 9.Kanazawa University, 10.Tohoku University, 11.Kyoto University, 12.Sodankyla Geophysical Observatory, Finland, 13.Finnish Meteorological Institute, Helsinki, Finland)

Keywords:Arase, EISCAT, pulsating aurora

Wave-particle interactions with lower band whistler-mode chorus waves (LBC) near the equator result in electron precipitation with energies ranging from 1-100 keV, leading to the pulsating aurora (PsA). Recent studies have shown that sub-relativistic/relativistic electrons with energies of several hundred of keV to several MeV are scattered by chorus waves that propagates to high latitudes along the field line, and these electrons precipitate into the mesosphere at an altitude of 60-80 km simultaneously with PsA (Miyoshi et al., 2015, 2020, 2021). We investigate high-energy electron precipitation during PsA events at Tromsø, Norway, from 02:00 to 06:00 UT on March 12, 2022, using data from the Arase satellite and the EISCAT radar. We estimate the electron energy spectrum from EISCAT observations. The analysis confirmed that electron precipitation occurred in wide energy range, and particularly strong precipitation was observed at energies of several tens of keV, and the estimated maximum energy of the precipitating electrons is ~300 keV. We then derived the pitch angle diffusion coefficient of electrons through chorus wave particle interactions using the Arase/PWE OFA data. Our result indicates that the estimated life time from a quasi-linear theory is comparable to the theoretical strong diffusion limit, implying that the observed plasma waves in the magnetosphere drive strong precipitation observed by the EISCAT radar. Moreover, our analysis confirms that chorus waves propagate to the higher latitudes can resonate more energetic electrons as shown in the estimation of the pitch angle diffusion coefficient. Considering these analyses, we conclude that the pitch angle scattering by LBC along the field line leads to wide energy electron precipitation from a few keV to more than 100 keV during PsA, as observed by the EISCAT radar.