[P-EM11] Dynamics of the Inner Magnetospheric System

[PEM11-P14] Characteristics of oxygen ion supply and energization in the inner magnetosphere during magnetic storms: Arase observations

*Kunihiro Keika¹, Retsu Miyamoto¹, Satoshi Kasahara¹, Shoichiro Yokota², Tomoaki Hori³, Yoshizumi Miyoshi³, Iku Shinohara⁴, Ayako Matsuoka⁵ (1.Graduate School of Science, The University of Tokyo , 2.Graduate School of Science, Osaka University, 3.Institute for Space-Earth Environmental Research, Nagoya University, 4.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 5.Graduate School of Science, Kyoto University)

Keywords:inner magnetosphere, ring current, oxygen ions of ionospheric origin, magnetic storms

This study investigates the supply and energization of singly-charged oxygen ions (O+) in the inner magnetosphere. O+, which originate from the upper ionosphere, can make a significant contribution to the ion pressure in the inner magnetosphere when the ion pressure is enhanced and in turn a magnetic storm occurs. It is well known that the pressure ratio of O+ to hydrogen ions (H+) increases as a storm develops. Our recent studies [Keika et al., 2018, GRL; 2022, JGR] indicated that the O/H ratio differs between ion energy ranges at radial distances of >5; the ratio is higher for higher energies. A preliminary study that focuses on impulsive pressure variations shows that the ratio increases mostly at the time of substorm injections. We here examine (1) occurrence characteristics of the energy-dependent O/H ratios associated with substorm injections and (2) temporal and spatial variations of phase space densities during the entire period of a storm including both main and recovery phases. We also perform (3) a statistical study using Arase data for about 50 magnetic storms that occurred in Years 2017-2021. These analyses aim to determine the dependence of the O/H ratio on energy (or magnetic moment, mu), locations, storm phases, and solar wind drivers. This comprehensive study will provide important clues to a better understanding of O+ supply and preferential energization in the inner magnetosphere and near-Earth magnetotail.

[1] Keika, K., et al., https://doi.org/10.1029/2018GL080047

[2] Keika, K., et al., https://doi. org/10.1029/2021JA029786