[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P22] A Comparative study of ring current ion and electron fluxes in two moderate geomagnetic storms based on Arase measurements

*Yuki Obana¹, Akimasa Yoshikawa¹, Naomi Maruyama², Atsuki Shinbori³, Satoko Nakamura³, Chae-Woo Jun³, Tomoaki Hori³, Yoshizumi Miyoshi³, Kumiko K. Hashimoto⁴, Atsushi Kumamoto⁵, Masahiro Kitahara⁵, Fuminori Tsuchiya⁵, Yoshiya Kasahara⁶, Ayako Matsuoka⁷, Yochi Kazama⁸, Shiang-Yu Wang⁸, Kazushi Asamura⁹, Iku Shinohara⁹, Shoichiro Yokota¹⁰, Kunihiro Keika¹¹, Satoshi Kasahara¹¹ (1.Kyushu University, 2.University of Colorado Boulder, 3.Nagoya Univsersity, 4.Kibi International University, 5.Tohoku University, 6.Kanazawa University, 7.World Data Center for Geomagnetism, Kyoto, 8.Academia Sinica, 9.ISAS, JAXA, 10.Osaka University, 11.The University of Tokyo)

Keywords:inner-magnetosphere, plasmasphere, ring current

Using the low-energy and mid-energy plasma instrument (LEPi, LEPe, MPEi, MEPe) onboard the Arase satellite, we can comprehensively investigate the fluxes of electrons and ions with different energies. Also, the in-situ electron density can be estimated by using the upper hybrid resonance frequencies detected from the plasma wave spectrum obtained by the plasma wave experiment (PWE).

The geomagnetic storm that commenced on 8 September 2017 has a Dst minimum of -147nT and appears to be a medium-sized magnetic storm at first glance, but it is known that it was a peculiar magnetic storm in various ways. For example, it is an extreme erosion of the plasmasphere to around L=1.5, and a strong SAPS generation.

Our previous research suggested that this extreme erosion of the plasmasphere was the result of a convective electric field that continued to penetrate into the magnetic equatorial region for more than 6 hours, however, the reason for the continuation of the convection field was unclear. We therefore compare the evolution of ring current particles during this peculiar magnetic storm to the magnetic storm which commenced on 25 August 2018, which has a similar Dst minimum (-175nT).

The following are the current results.
The nightside plasmasphere was almost entirely eroded during the main phase of the 2017 storm. On the other hand, the plasmasphere was eroded to around L = 2.5 in the main phase of the 2018 storm. Furthermore, in the main phase of the 2018 storm, H⁺, He⁺, and O⁺ in the energy range of 10-180 keV and electrons in the energy range 7-25 keV show a sharp increase around L~4, so that the plasma sheet injection seems to stop around L~4. On the other hand, in the main phase of the 2017 storm, the ion flux peaked around L~3 and gradually decreased to around L~2. At the 2017 storm, fluxes of the 50-180 keV H⁺ and 10-120 keV O⁺ increased significantly around L=2-4.

In this talk, we will show the details of the evolution of ring current electrons and ion fluxes, and discuss how the characteristics of the two geomagnetic storms are different.