[P-EM16] Dynamics of Earth's Inner Magnetosphere and Initial Results from Arase

[PEM16-06] Magnetic field dipolarization and its associated ion flux variations in the deep inner magnetosphere: Arase and Michibiki-1 satellite observations

*Masahito Nose¹, Ayako Matsuoka², Satoshi Kasahara³, Shoichiro Yokota⁴, Mariko Teramoto⁵, Kunihiro Keika³, Reiko Nomura⁶, Akiko Fujimoto⁷, Nana Higashio⁶, Hideki Koshiishi⁶, Shun Imajo¹, Yoshimasa Tanaka⁸, Manabu Shinohara⁹, Iku Shinohara², Yoshizumi Miyoshi⁵ (1.Graduate School of Science, Kyoto University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.Graduate School of Science, The University of Tokyo, 4.Graduate School of Science, Osaka University, 5.Institute for Space-Earth Environmental Research, Nagoya University, 6.Tsukuba Space Center, Japan Aerospace Exploration Agency, 7.International Center for Space Weather Science and Education, Kyusyu University, 8.National Institute of Polar Research, 9.Kagoshima National College of Technology)

The Arase satellite observed clear dipolarization signatures at L~4.6–4.8 and magnetic local time (MLT)~5.5–5.7 h around 15:00 UT on 27 March 2017 when Dst~−70 nT. Strong magnetic field fluctuations were embedded in the dipolarization and their characteristic frequency was close to the local gyrofrequency of O⁺ ions. After the dipolarization, O⁺ flux was enhanced at 5–20 keV, while H⁺ flux showed no clear variations. These observations provide evidence for the selective acceleration of O⁺ ions by the magnetic fluctuations. At the same time, the Michibiki-1 satellite was located at L=6.6–7.1 and MLT=22.2–23.9 h. In four events out of six, magnetic field dipolarization was not identified at premidnight by Michibiki-1 but near dawn by Arase. This surprising MLT distribution of dipolarization in the inner magnetosphere may be attributed to an eastward skewing of partial ring current that is created during the storm main phase.