[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P02] Arase observations of field and plasma characteristics in the source region of a storm-time auroral brightening arc

*Liwei Chen¹, Kazuo Shiokawa¹, Yoshizumi Miyoshi¹, Shin-ichiro Oyama^1,2, Chae-Woo Jun¹, Yasunobu Ogawa², Keisuke Hosokawa³, Yoichi Kazama⁵, Shiang-Yu Wang⁵, Sunny Wing-Yee Tam⁴, Tzu-Fang Chang^1,4, Bo-Jhou Wang⁵, Kazushi Asamura⁶, Satoshi Kasahara⁷, Shoichiro Yokota⁸, Tomoaki Hori¹, Kunihiro Keika⁷, Yasumasa Kasaba⁹, Atsushi Kumamoto⁹, Fuminori Tsuchiya⁹, Masafumi Shoji¹, Yoshiya Kasahara¹⁰, Ayako Matsuoka¹¹, Iku Shinohara⁶, Shun Imajo¹¹ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Polar Research, 3.The University of Electro-Communications, 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)

Keywords:Substorm, Aurora, inner-magnetosphere

Since the plasma and electromagnetic conditions can be very different with quiet time during geomagnetic storm, there will be differences between substorms that occur during geomagnetic quiet time and storm time. In this presentation, we show a unique auroral substorm study during a geomagnetic storm using a ground-based all-sky camera and the Arase satellite at L~6. The auroral arcs of interest were observed on September 8, 2017, at Tromsø, Norway (69.6^oN, 19.2^oE, in geographic coordinates; 66.7°N in geomagnetic coordinates). The ground-based electron-multiplying charge-coupled device (EMCCD) camera observed that the auroral arcs in the south edge of field-of-view (FOV) started their poleward expansion at ~2040 UT, while the footprint of the Arase satellite was moving southeastward and crossed the poleward-expanding arc at the southwestern edge of FOV at ~2043 UT. The Dst index indicates that this substorm occurred during the recovery phase of a geomagnetic storm with a minimum Dst of -122 nT at 0200 UT on September 8. The ion and electron energy spectra from the Arase on-board omnidirectional particle measurements show clear ion and electron flux enhancements before and at the timing of the footprint crossing of the poleward-expanding aurora. A series of field-aligned Poynting flux enhancements were found to appear simultaneously with the ion and electron flux enhancement. The magnetic field data suggest the existence of field-aligned current (FAC) when the satellite footprint crosses the poleward-expanding arc. From these observations, we suggest that a pressure gradient at high magnetic latitudes in the inner magnetosphere contributes to the formation of FAC and the auroral poleward expansion. In the presentation, we will also discuss these results with previous conjugate observations of substorm auroral brightening during geomagnetically quiet time, in light of differences of magnetospheric processes between quiet-time and storm-time substorms in the inner magnetosphere.