[P-PS06] [EJ] あかつき金星周回1.5年とその科学成果

[PPS06-02] Mesoscale to planetary-scale motions in the Venus atmosphere revealed by cloud tracking with Akatsuki IR and UV images

*堀之内 武¹、村上 真也²、佐藤 毅彦²、渡部 重十³、神山 徹⁴、小郷原 一智⁵、今村 剛⁶、高木 征弘⁷、樫村 博基⁸、Peralta Javier²、Limaye Sanjay¹⁰、佐藤 隆雄²、中村 正人²、山田 学⁹ (1.北海道大学地球環境科学研究院、2.宇宙科学研究所、3.北海道情報大学、4.産総研、5.滋賀県立大学、6.東京大学、7.京都産業大学、8.神戸大学、9.千葉工業大学、10.University of Wisconsin、11.Southwest Research Institute)

キーワード：Venus, Atmosphere, Jet, Mesoscale motion, Hydrodynamic instability, Superrotation

Since its orbital insertion on Dec 7, 2015, Akatsuki has been providing us with high quality images at multiple wavelengths for both the dayside and the nightside of Venus [1]. In this presentation, we present results based on cloud tracking. Owing to the high quality and a newly developed cloud tracking algorithm with novel error evaluation [2,3], we are able to conduct cloud tracking with unprecedented quality and resolution. In earlier studies, snapshots of wind distributions are shown mainly for demonstrations, but now we are able to seize it with confidence. We found sub-planetary-scale (down to mesoscale in terms of the Earth’s atmosphere) divergent and vertical motions on the dayside cloud top of Venus by using images from UVI, the ultraviolet imager of Akatsuki. The result suggests the existence of quasi-two-dimensional turbulent motion as well as mesoscale three-dimensional features. We also found a jet-like flow in the lower-cloud layer from the night-side images from IR2, an infrared imager of Akatsuki. The equatorial jet has not been reported previously, so its emergence indicates some temporal variability at this level. Further study is ongoing. For example, we have found vortical motions that are likely associated with barotropic instability.