[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-06] Arase satellite observation of energetic ions to study the O+_H charge-exchange reaction

*Akimasa Ieda¹, Naritoshi Kitamura¹, Yoshizumi Miyoshi¹, Tomoaki Hori¹, Kazuhiro Yamamoto¹, Chae-Woo Jun¹, Shoichiro Yokota², Satoshi Kasahara³, Kunihiro Keika³, Iku Shinohara⁴ (1.Institute for space-Earth environmental research, Nagoya university, 2.Osaka university, 3.The university of Tokyo, 4.Institute of space and astronautical science)

Keywords:ring current, charge-exchange, magnetic storm, geocorona

The magnetic storm is characterized by the ring current that is located at several earth radii from Earth. The ring current develops during the storm main phase and decays during the storm recovery phase. The decay of ring current is often associated with the decay of atomic oxygen ions at 10-100 keV through charge-exchange reactions with geocoronal neutral hydrogen atoms. However, the charge-exchange cross section of this particle pair (O+_H) has been unclear at this energy range in theory and laboratory experiment. In this study, we clarify this charge-exchange cross section using Arase satellite observations. We selected a non-substorm interval during the recovery phase of a magnetic storm in May 2024 and compared 10-180 keV ions over a satellite pass and those of the next pass 9 hours later. The result of the comparison indicates that the charge-exchange cross section is close to each other between the O+_H and H+_H pairs at approximately 40 keV. This result indicates that the O+_H cross section measured by the past laboratory measurement was inaccurate by a factor of 2-10 at 10-100 keV. Conventional O+_H cross sections have been deduced at 10-100 keV using indirect methods like interpolation. Our result suggests that such cross sections are accurate within a factor of two.