講演情報
[PPS04-11]Interaction between the thermosphere and the cloud-level atmosphere of Venus inferred from simultaneous observations by Hisaki and Akatsuki★Invited Papers
*奈良 佑亮1、今村 剛1、吉川 一朗1、吉岡 和夫1、益永 圭2、山崎 敦3、渡部 重十4、山田 学5、Lee Yeon Joo1、寺田 直樹6、関 華奈子7 (1.東京大学大学院新領域創成科学研究科、2.Swedish Institute of Space Physics、3.宇宙航空研究開発機構宇宙科学研究所、4.北海道情報大学、5.千葉工業大学、6.東北大学地球物理学専攻惑星大気物理学分野、7.東京大学大学院理学系研究科)
キーワード：
金星、あかつき、ひさき、同時観測
Recent studies on the Venus’ upper atmosphere suggest that atmospheric waves may propagate from the middle atmosphere to the thermosphere (e.g., Masunaga et al., 2017). To understand the role of vertically propagating waves, simultaneous observations of the cloud-level atmosphere and the thermosphere of Venus are necessary.
Hisaki and Akatsuki observed Venus simultaneously in June 2017 and we analyzed the EUV OI (130.4 nm and 135.6 nm) dayglow obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on Hisaki and the UV contrast (365 nm) obtained by the Ultraviolet Imager (UVI) on Akatsuki. The OI emissions reflect the column density of the oxygen and the electron in the thermosphere, and the UV images reflect the spatial distributions of unidentified absorbers at the cloud top.
Analyzing the time series of the OI dayglow emissions and the UV contrast obtained by UVI, we identified periodicities of 3.5 days in both data. The wind velocity deduced with cloud tracking from UV images suggests that the 3.5-day periodicity can be associated with Kelvin waves at the cloud top; however, Kelvin waves should decay with height through radiative damping and will not reach the thermosphere. We propose an indirect process in which the Kelvin waves change the wind field periodically and this oscillating wind influences the vertical propagation of small-scale gravity waves.
Hisaki and Akatsuki observed Venus simultaneously in June 2017 and we analyzed the EUV OI (130.4 nm and 135.6 nm) dayglow obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on Hisaki and the UV contrast (365 nm) obtained by the Ultraviolet Imager (UVI) on Akatsuki. The OI emissions reflect the column density of the oxygen and the electron in the thermosphere, and the UV images reflect the spatial distributions of unidentified absorbers at the cloud top.
Analyzing the time series of the OI dayglow emissions and the UV contrast obtained by UVI, we identified periodicities of 3.5 days in both data. The wind velocity deduced with cloud tracking from UV images suggests that the 3.5-day periodicity can be associated with Kelvin waves at the cloud top; however, Kelvin waves should decay with height through radiative damping and will not reach the thermosphere. We propose an indirect process in which the Kelvin waves change the wind field periodically and this oscillating wind influences the vertical propagation of small-scale gravity waves.