[P-EM13] Dynamics of Magnetosphere and Ionosphere

[PEM13-04] Ionization of the mesosphere during substorm growth phase

*村瀬 清華¹、片岡 龍峰²、西山 尚典²、西村 耕司²、橋本 大志²、田中 良昌²、門倉 昭²、冨川 喜弘²、堤 雅基²、佐藤 薫³、笠原 慧³、三谷 烈史⁴、横田 勝一郎⁹、堀 智昭⁷、桂華 邦裕³、東尾 奈々⁵、高島 健⁴、笠原 禎也⁶、松田 昇也⁴、小路 真史⁷、松岡 彩子⁴、篠原 育⁴、三好 由純⁷、佐藤 達彦⁸ (1.総合研究大学院大学、2.国立極地研究所、3.東京大学、4.宇宙航空研究開発機構 宇宙科学研究所、5.宇宙航空研究開発機構、6.金沢大学、7.名古屋大学、8.日本原子力研究開発機構、9.大阪大学)

キーワード：大気電離、高エネルギー電子降下、サブストーム成長相

We report two mesospheric ionization events, both occurred during a substorm growth phase. The ionization reached at 68 km altitude at 2305 UT on 25 May 2017, and at 0000 UT on 25 July 2018, as identified by the PANSY radar at Syowa Station. Theoretically, the deep ionization events can be caused by the thinning of the magnetotail because of the small curvature radius of magnetic field lines at equator, which is comparable to the gyro radius of energetic electrons. Fortunately, the footprints of the Arase satellite passed nearby the Syowa Station during these two events, and we cannot find associated plasma waves to scatter energetic electrons, as expected from the curvature theory. In this study, we quantitatively evaluate the mesospheric ionization profiles by comparing the intensity of cosmic noise absorption as observed by the imaging riometer at Syowa Station, and the simulated one using the PHITS code with the input data of energetic electron flux as observed by the Arase satellite.