[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-13] 超低周波波動によって駆動される高緯度電離圏振動：SuperDARNレーダーとGNSS-TEC法を用いた同時観測結果

*新堀 淳樹¹、細川 敬祐²、堀 智昭¹、寺本 万里子³、Pavlo Ponomarenko⁴、尾花 由紀⁵、西谷 望¹、行松 彰⁶、大塚 雄一¹、西岡 未知⁷、Perwitasari Septi⁷、熊本 篤志⁸、土屋 史紀⁹、松田 昇也¹⁰、笠原 禎也¹⁰、松岡 彩子¹¹、三好 由純¹、篠原 育¹² (1.名古屋大学宇宙地球環境研究所、2.電気通信大学、3.九州工業大学、4.サスカチュアン大学、5.九州大学国際宇宙惑星環境研究センター、6.国立極地研究所、7.情報通信研究機構、8.東北大学大学院理学研究科地球物理学専攻、9.東北大学惑星プラズマ・大気研究センター、10.金沢大学、11.京都大学大学院理学研究科附属地磁気世界資料解析センター、12.JAXA宇宙科学研究所)

キーワード：高緯度電離圏、超低周波波動、SuperDARNレーダー、GNSS-TEC、外部電場、アルベン波

To elucidate the generation mechanism of ionospheric electron density variation from sub-auroral to high latitudes associated with Pc 5 ultra-low frequency (ULF) waves, we analyzed global navigation satellite system (GNSS)-total electron content (TEC), ionospheric plasma flow observed by the Super Dual Auroral Radar Network (SuperDARN), and electron density in the inner magnetosphere measured by the Arase satellite. On 23 November 2022, the SuperDARN Prince George (PGR) radar in the dusk sector detected meridional plasma flow oscillations with a period and amplitude of 5 min and 10-60 m/s, respectively. The plasma flow oscillations started at around 01:10 UT and persisted at least until 03:30 UT over a magnetic latitude range of 65-72 degrees, having a larger amplitude with increasing magnetic latitude. The electron density showed no sharp gradient in this inner magnetosphere pass, indicating that the plasmasphere extended beyond the apogee of the Arase satellite (6.1 Re) under a very quiet geomagnetic condition. A detailed comparison between the SuperDARN radar and GNSS-TEC data shows that the meridional plasma flow oscillations appeared in the mid-latitude trough and auroral oval (increased TEC region). The equatorward boundary of the auroral oval was located at 72-74 degrees in magnetic latitude. The 15-min detrended TEC measured over Fort Simpson, inside the field-of-view of PGR, showed a similar oscillation to the ionospheric plasma flow variation. Applying a spectral analysis to the detrended TEC and meridional plasma flow oscillations, we identified a phase difference of ~135 degrees (~1.9 min) between them. This result is consistent with a simple model calculation with an oscillating electric field with a period of 5 min and an amplitude of 30 m/s for the ExB drift. On the basis of these observational and model calculation results, the TEC oscillation can be explained by the upward and downward motion of the ionosphere due to an external electric field caused by Alfvén waves propagating along magnetic field lines from the duskside magnetosphere.