[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-P15] Initial study of a substorm onset auroral arc on 28 December 2018 by a ground EMCCD camera and the Arase satellite at L~5

*Liwei Chen¹, Kazuo Shiokawa¹, Yoshizumi Miyoshi¹, Shin-ichiro Oyama¹, Yasunobu Ogawa², Keisuke Hosokawa¹², Ryuho Kataoka², Yoichi Kazama⁵, Shiang-Yu Wang³, Sunny W. Y. Tam⁵, Tzu-Fang Chang^1,4, Bo-Jhou Wang⁵, Kazushi Asamura⁶, Satoshi Kasahara⁷, Shoichiro Yokota⁸, Tomoaki Hori¹, Kunihiro Keika⁷, Yasumasa Kasaba⁹, Masafumi Shoji¹, Yoshiya Kasahara¹⁰, Ayako Matsuoka¹¹, Iku Shinohara⁶ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Polar Research, 3.National Cheng Kung University, 4.Institute of Space and Plasma Sciences, National Cheng Kung University, 5.Institute of Astronomy and Astrophysics, Academia Sinica, 6.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 7.University of Tokyo, 8.Osaka University, 9.Tohoku University, 10.Kanazawa University, 11.Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, 12.The University of Electro-Communications)

Keywords:substorm, auroral arc, conjugate observation

While many substrom-related observations have been made, few conjugate observations of substorm auroral arcs have been reported in the inner magnetosphere at L~4-6. In this study we present a conjugate observation of a substorm brightening auroral arc during a substorm onset observed by the Arase satellite and a ground-bases EMCCD camera. The event was observed at Gakona, Alaska (62.39^oN, 214.78^oE) on 28 December 2018. The camera showed that a west-east auroral arc moved from the east at ~0730 UT and subsequently broke up poleward at ~0743 UT. The ionospheric footprint of the Arase satellite was moving equatorward from the northwest to the southeast around the center in the field-of-view of the EMCCD camera. The maximum AE index reached ~600 nT during the auroral breakup, indicating the occurrence of a substorm. The particle data of low energy electrons and medium energy ions show the characteristic variations and energizations around the timing of the arc crossing by Arase. The magnetic and electric field data presented a series of quasi-periodic fluctuations, and their cross products show a series of field-aligned Poynting flux flowing earthward and equator-ward alternately at the timing around the crossing. Based on these observations we will discuss the generation mechanisms of the substorm auroral arc in the source region in the inner magnetosphere.