[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-P04] Geotail, MMS, Arase, and Cluster satellite observations of slow earthward flow before a substorm onset

*Akimasa Ieda¹, Naritoshi Kitamura¹, Rumi Nakamura^1,2, Yoshizumi Miyoshi¹, Tomoaki Hori¹, Shinobu Machida¹, Masahito Nose¹, Tsugunobu Nagai³, Yukinaga Miyashita⁴, Yoshifumi Saito³, Shoichiro Yokota⁵, Barbara L Giles⁶, Daniel J Gershman⁶, Christopher T Russell⁷, Fuminori Tsuchiya⁸, Atsushi Kumamoto⁸, Yoshiya Kasahara⁹, Satoko Nakamura¹, Ayako Matsuoka¹⁰, Iku Shinohara³, Kazushi Asamura³, Shiang-Yu Wang¹¹, Yoichi Kazama¹¹, Chae-Woo Jun¹, Satoshi Kasahara¹², Kunihiro Keika¹², Takefumi Mitani³, Takeshi Takashima³, Nana Higashio³, Christopher M Carr¹³, Iannis Dandouras¹⁴, Andrew Fazakerley¹⁵, Patrick W Daly¹⁶ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Austrian Academy of Sciences, 3.JAXA, 4.KASSI, 5.Osaka University, 6.NASA/GSFC, 7.UCLA, 8.Tohoku University, 9.Kanazawa University, 10.Kyoto University, 11.ASIAA, 12.University of Tokyo, 13.Imperial college London, 14.Université de Toulouse, 15.University College London, 16.MPI für Sonnensystemforschung)

Keywords:substorm, magnetotail, magnetic reconnection

A substorm onset occurred at 1749 UT on August 4, 2017, with a peak of -700 nT in the AL index. Geotail, MMS, Arase, and Cluster satellites were located in the pre-midnight sector and observed magnetic dipolarization within 2 min of the onset. Geotail and MMS were located in the plasma sheet boundary layer of the magnetotail and were separated by 2 Earth radius (Re): Geotail was located at (X, Y) = (-16.8, 3.1) Re in aberrated GSM coordinates, and MMS was located at (X, Y) = (-18.4, 3.0) Re. Geotail and MMS were located 2.4 and 1.4 Re north of a model neutral sheet, respectively. Geotail observed a slow earthward ion flow (150 km/s) 5 min before the substorm onset. MMS satellites were located closer to the neutral sheet but did not detect a corresponding ion flow. Therefore, the slow earthward flow does not indicate the classic near-Earth magnetic reconnection.