[P-EM16] Dynamics of Earth's Inner Magnetosphere and Initial Results from Arase

[PEM16-P15] Oxygen torus near the plasmapause observed by Arase

*能勢 正仁¹、松岡 彩子²、熊本 篤志³、笠原 禎也⁴、寺本 万里子⁵、土屋 史紀³、松田 昇也⁵、小路 真史⁵、尾花 由紀⁶、今城 峻¹、生松 聡¹、山本 和弘¹、野村 麗子⁷、藤本 晶子⁸、篠原 育²、三好 由純⁵ (1.京都大学大学院理学研究科、2.宇宙航空研究開発機構宇宙科学研究所、3.東北大学大学院理学研究科、4.金沢大学総合メディア基盤センター、5.名古屋大学宇宙地球環境研究所、6.大阪電気通信大学工学部、7.宇宙航空研究開発機構つくば宇宙センター、8.九州大学国際宇宙天気科学・教育センター)

Using the magnetic field and plasma wave data obtained by the fluxgate magnetometer (MGF) and plasma wave experiment/high-frequency wave receiver and onboard frequency analyzer (PWE/HFA and OFA) instruments on board the Arase satellite, we search for enhancements of O⁺ ion density in the deep inner magnetosphere known as “the oxygen torus”. We estimate the local plasma mass density (rho_L) and the local electron number density (n_eL) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band, respectively. The average ion mass (M) can be calculated by M~rho_L/n_eL under the assumption of quasi-neutrality of plasma. Preliminary analysis of some events at dawn, in which toroidal standing Alfvén waves appear clearly during the storm recovery phase, reveals that M is enhanced in the vicinity of the plasmapause, implying formation of the oxygen torus. In presentation, we will show more detailed analysis results and discuss the formation mechanism of the oxygen torus.