[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P19] Long term variations of He++ ions in the inner magnetosphere; Arasa LEPi observations

*西田 結衣¹、永谷 朱佳理¹、三好 由純¹、浅村 和史²、Kistler Lynn³、篠原 育² (1.名古屋大学宇宙地球環境研究所、2.宇宙航空研究開発機構、3.ニューハンプシャー大学)

キーワード：あらせ衛星、内部磁気圏、アルファ粒子

He++ ions present in the Earth's magnetosphere is believed to originate from the solar wind; however the detailed variations in them are not yet understood. Observations of various types of ions have been conducted since 2017 using the two ion analyzers, LEP-i and MEP-i, onboard the Arase satellite. Note that satellites that have measured He++ ions in the inner magnetosphere are limited, with only the Arase satellite having done so in the 2010s. Therefore, it is crucial to utilize the valuable observational data from LEP-i. In this study, we analyzed Time-of-Flight (TOF) data from LEP-i to investigate the long-term variations of He++ ions in the inner magnetosphere and their dependence on solar activity. The observations from the Arase satellite have been conducted from April 1, 2017, to the present. This period corresponds to the declining phase of Solar Cycle 24 through Solar Cycle 25. Analyzing the observational data obtained with LEP-i, we find that there is a strong correlation between the He++ ion counts and Kp and F10.7. We will discuss the long-term variations of He++ ions by comparing the previous observations by GEOS-1/2.