[P-CG18] 惑星大気圏・電磁圏

[PCG18-12] 火星ダストストーム発達中における水素および酸素大気光の周期変動

*益永 圭¹、寺田 直樹²、吉田 奈央²、黒田 剛史²、吉岡 和夫³、木村 智樹²、土屋 史紀²、村上 豪⁴、山崎 敦⁴、吉川 一朗³ (1.コロラド大学、2.東北大学、3.東京大学、4.宇宙科学研究所)

キーワード：火星、ひさき衛星、大気光、ダストストーム

Analyzing extreme ultraviolet (EUV) spectra of the Martian upper atmosphere obtained from the Hisaki space telescope, we study variations of hydrogen (HI Ly-β) and oxygen (OI 135.6 nm) airglow during a rapid expansion of a regional dust storm that occurred in Mars Year 33. We find that Ly-β brightness did not vary with the solar EUV flux but significantly increased over the observation period (L_S=213°-232°), while OI 135.6 mainly varied with the solar EUV flux. After subtracting the seasonal and solar effects from Ly-β and OI 135.6 nm brightness, respectively, it was found that their residual brightness varied with a ~6-8-day periodicity and that the OI 135.6 nm residual brightness approximately varied in quadrature with that of Ly-β. The variation level for both emissions was ~20-40% for the whole disk. This indicates that when hydrogen atoms are globally produced by water vapor transported from the lower atmosphere during the dust storm expansion, the amount of oxygen atoms significantly decreases in the upper atmosphere of Mars. In this presentation, we discuss a role of atmospheric waves such as baroclinic waves that usually present in the northern hemispheric lower atmosphere in this season as a possible candidate to cause the periodic airglow variations in the upper atmosphere. We also discuss a cause of the anti-correlation between the hydrogen and oxygen airglow emissions, by analyzing variations of other emission lines such as OII 83.4 nm and ArI 106.6 nm, and CO bands as well as the hydrogen and oxygen emissions.