[P-EM15] 太陽地球系結合過程の研究基盤形成

[PEM15-P12] Thermoshperic He variations associated with two storms on February and March, 2023: the NIRAS-2 observations at Longyearbyen (78.1°N, 16.0°E), Svalbard.

*西山 尚典^1,2、鍵谷 将人³、津田 卓雄⁴、Bag Tikemani¹、岩佐 祐希⁵、小川 泰信^1,2、Sigernes Fred⁶ (1.国立極地研究所、2.総合研究大学院大学 極域科学専攻、3.東北大学 惑星プラズマ・大気研究センター、4.電気通信大学、5.産業技術総合研究所 計量標準総合センター 、6.University centre in Svalbard)

キーワード：準安定性ヘリウム原子、上部熱圏、地上分光観測、磁気嵐、極冠域、EISCATスヴァールバルレーダー

Despite the low density of neutral metastable helium, He(2³S), in the upper thermosphere and lower exosphere (typically less than 10 atoms cm^-3), its bright, ~1 kR, emission signature at 1083 nm makes this airglow feature an attractive potential candidate for remote sensing of the neutral atmospheric temperature and dynamics in this region. Our SWIR imaging spectrograph installed at the KHO Longyearbyen (78.1°N, 16.0°E), NIRAS-2, has a capability to measure the metastable He emission that is blended with Q-branch of OH (5,2) emission. It actually demonstrated that strong enhancement of the He emission took place during twilight conditions when metastable He in the upper thermosphere was sufficiently illuminated. Preliminary analysis was done for He variations associated with two magnetic storms on February and March, 2023. After onset of the February storm, nighttime He column denisty estimated from intensity of the He emission was decreased immediately, and the depression lasted at least a few days. MSIS 2.1calculation can reproduce the He depression above KHO, and suggest that He density at 450 km was reduced to 30% of one during quiet conditions. In this presentation, we would like to show more detailed analysis results.