[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P09] Low energy ions observed by Arase during spacecraft charging events

*Yumika Sue¹, Satoshi Kasahara¹, Kazushi Asamura², Ayako Matsuoka³, Rino Takahara¹, Yoshizumi Miyoshi⁴ (1.The university of Tokyo , 2.Japan Aerospace Exploration Agency, 3.Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, 4.Institute for Space-Earth Environement Research, Nagoya University)

Keywords:Arase, Spacecraft charging, FALEO

In the inner magnetosphere, energy-dispersed flux enhancements of field-aligned low-energy oxygen ions (FALEO) are observed during magnetic disturbances. This phenomenon is thought to be the result of O+ ions’ upwelling from the ionosphere reaching the inner magnetosphere with some acceleration and is important to understand the mechanism of atmospheric outflows.
However, it has been unclear how often such O+ outflows are observed during magnetic disturbances. In this research, taking advantage of spacecraft charging, we observed very low-energy oxygen ions, which were difficult to detect in previous research. We identified 26 events of very-low-energy proton (VLEP) flux enhancements due to spacecraft charging, observed by LEP-i onboard Arase satellite in 2017-2023.
All are accompanied by O+ flux enhancements. Some events are characterized by O+ energy higher than protons by a few hundred eV to a few keV, and others are with almost the same energy as protons. In addition, all of those ions have field-aligned pitch angle distribution. These indicate that during magnetic disturbance events in which VLEP are observed, O+ outflows always exist, with or without significant acceleration (FALEO or very-low-energy oxygen ions, VLEO, respectively).
Directions of VLEO are ionosphere-to-equator or opposite, similar to recent FALEO studies.