[P-EM13] Inner magnetosphere: Recent understanding and new insights

[PEM13-25] Multiple Satellite Observations of Oxygen Torus in the Inner Magnetosphere

*Masahito Nose¹, Ayako Matsuoka², Atsushi Kumamoto³, Yoshiya Kasahara⁴, J Goldstein^5,6, Mariko Teramoto¹, Fuminori Tsuchiya³, Shoya Matsuda², Masafumi Shoji¹, Shun Imajo¹, Oimatsu Satoshi⁷, Kazuhiro Yamamoto⁷, Yuki Obana⁸, Reiko Nomura⁹, Akiko Fujimoto¹⁰, Iku Shinohara², Yoshizumi Miyoshi¹, W S Kurth¹¹, C A Kletzing¹¹, C W Smith¹², R J MacDowall¹³ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.Graduate School of Science, Tohoku University, 4.Information Media Center, Kanazawa University, 5.Space Science and Engineering Division, Southwest Research Institute, 6.University of Texas at San Antonio, 7.Graduate School of Science, Kyoto University, 8.Faculty of Engineering, Osaka Electro-Communication University, 9.National Astronomical Observatory of Japan, 10.Kyushu Institute of Technology, 11.Department of Physics and Astronomy, University of Iowa, 12.Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, 13.Solar System Exploration Division, Goddard Space Flight Center)

A recent study employing the Arase and Van Allen Probes A satellites at different MLT revealed an event in which the inner magnetospheric O⁺ density enhancement (know as the dense oxygen torus) does not extend over all MLT. Rather, the torus is skewed toward the dawn sector, being described more precisely as a crescent-shaped torus or a pinched torus [Nosé et al., 2018]. In the reported event of 24 April 2017, Arase flying in the morning sector detected an enhancement of the average plasma mass up to ~3.5 amu around L=4.9–5.2, while Van Allen Probe A flying in the afternoon sector observed no clear enhancements in the average plasma mass. In the present study, we focus on simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probes A and B satellites on 12 September 2017. For this event the orbital configuration of the satellites is opposite to that in the study by Nosé et al. [2018]; that is, Arase is in the afternoon and the Van Allen Probes are in the morning. It is found that only Probe B observed a clear enhancement in the average plasma mass up to ~4 amu around L=3.5 and MLT=9.0 hr. This result demonstrates that the crescent-shaped O⁺ torus is not a unique (single-event) occurrence, and thus may be a general feature of the density enhancement in the inner magnetosphere.