*Akimasa Ieda1, Naritoshi Kitamura1, Rumi Nakamura1,2, 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.