Cloud structure of Venus revealed by new observations using Akatsuki spacecraft and ground-based telescope

• Project/Area Number: 19K14786
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Hokkaido Information University
• Principal Investigator: Sato Takao 北海道情報大学, 経営情報学部, 准教授 (50633509)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥2,990,000 (Direct Cost: ¥2,300,000、Indirect Cost: ¥690,000); Fiscal Year 2021: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000); Fiscal Year 2020: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000); Fiscal Year 2019: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
• Keywords: 金星 / 雲層構造 / 探査機「あかつき」 / 地上望遠鏡 / 放射伝達 / 微量大気

Outline of Research at the Start

金星は地球の双子星だが全く異なる気候進化を遂げた．その大きな要因である厚い硫酸雲を探査機と地上望遠鏡から観測的に調べる．研究は3つの小課題に分けて実施する．まず，探査機「あかつき」の2μmカメラ画像から雲の高度や厚みの緯度及び地方時依存性を明らかにする．また雲構造を変化させる大気運動を調べるため，鉛直運動の指標となる一酸化炭素分布を推定し雲追跡手法で得られる水平風との関係を調査する．さらに，地上望遠鏡を用いた近赤外高分散分光観測から雲形成や大気運動の指標となる微量大気の時空間変動を調べる．研究成果は大気大循環モデルやデータ同化手法による大気現象の再現や気候システムの解明に必要な制約情報となる．

Outline of Final Research Achievements

Optically thick clouds of sulfuric acid on Venus were observationally investigated by new observations using Akatsuki spacecraft and a ground-based telescope, IRTF. From near-infrared images of Akatsuki, the cloud tops were found to have an equatorially symmetric structure. The average cloud top altitude showed a gradual decrease from low to mid latitudes. It rapidly dropped from mid to high latitudes. The cloud tops on Venus are basically stable for nearly ten years in light of previous studies using past spacecraft data. The stationary gravity wave features first discovered in mid-infrared images of Akatsuki were also seen in the near-infrared images. The bright contrast of the features could be interpreted as resulting from the difference in cloud top altitude of a few hundred meters. The cloud tops derived from CO2 lines obtained by a high-resolution infrared spectroscopy using IRTF qualitatively supported the results from the near-infrared images of Akatsuki.

Academic Significance and Societal Importance of the Research Achievements

全球を覆う光学的に厚い硫酸雲は金星全体の熱収支を支配しており，この振る舞いが金星の気候進化に大きく影響してきたと考えられる．従って，雲層構造の空間分布とその時間変動の理解は，金星の気候システムを解明する上で重要な基礎情報となる．本研究では，欧州探査機Venus Express以降では唯一となる雲層の詳細観測を実施した探査機「あかつき」と地上望遠鏡による観測データを用いて，雲頂高度分布と山岳波に起因した定在構造を含む微細構造について新たな知見を得た．これらは大気大循環モデルやデータ同化手法による大気現象の再現や気候システムの解明に必要な制約情報となった．

Research Products

• [Journal Article] A new constraint on HCl abundance at the cloud top of Venus (2023)
  • Author(s): Sato Takao M.、Sagawa Hideo
  • Journal Title: Icarus Volume: 390 Pages: 115307-115307
  • DOI: 10.1016/j.icarus.2022.115307
  • Peer Reviewed
• [Journal Article] Correlation of Venusian Mesoscale Cloud Morphology Between Images Acquired at Various Wavelengths (2022)
  • Author(s): Narita M.、Imamura T.、Lee Y. J.、Watanabe S.、Yamazaki A.、Satoh T.、Taguchi M.、Sato T. M.、Fukuhara T.、Yamada M.、Kouyama T.、Iwagami N.
  • Journal Title: Journal of Geophysical Research: Planets Volume: 127 Issue: 6
  • DOI: 10.1029/2022je007228
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Modeling a point-spread function originating from multiple reflection of light in the substrate of array sensor: the case of Akatsuki/IR2 (2022)
  • Author(s): Satoh Takehiko、Uemizu Kazunori、Ueno Munetaka、Kimata Masafumi、Sato Takao M.
  • Journal Title: Proceedings of SPIE - The International Society for Optical Engineering Volume: 12264 Pages: 18-18
  • DOI: 10.1117/12.2638444
  • Peer Reviewed
• [Journal Article] Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR (2021)
  • Author(s): Masahiro Akiba, Makoto Taguchi, Tetsuya Fukuhara, Takeshi Imamura, Toru Kouyama, Takao M. Sato
  • Journal Title: J. Geophys. Res.: Planets Volume: 126 Issue: 10
  • DOI: 10.1029/2020je006808
  • Peer Reviewed / Open Access
• [Journal Article] Unveiling of nightside cloud-top circulation of Venus atmosphere (2021)
  • Author(s): Kiichi Fukuya, Takeshi Imamura, Makoto Taguchi, Tetsuya Fukuhara, Toru Kouyama, Takeshi Horinouchi, Javier Peralta, Masahiko Futaguchi, Takeru Yamada, Takao M. Sato, Atsushi Yamazaki, Shin-ya Murakami, Takehiko Satoh, Masahiro Takagi, Masato Nakamura
  • Journal Title: Nature Volume: 595 Issue: 7868 Pages: 511-515
  • DOI: 10.1038/s41586-021-03636-7
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Venus night-side photometry with “cleaned” Akatsuki/IR2 data: Aerosol properties and variations of carbon monoxide (2021)
  • Author(s): Satoh Takehiko、Vun Choon Wei、Kimata Masafumi、Horinouchi Takeshi、Sato Takao M.
  • Journal Title: Icarus Volume: 355 Pages: 114134-114134
  • DOI: 10.1016/j.icarus.2020.114134
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] How waves and turbulence maintain the super-rotation of Venus’ atmosphere (2020)
  • Author(s): Horinouchi Takeshi、Hayashi Yoshi-Yuki、Watanabe Shigeto、Yamada Manabu、Yamazaki Atsushi、Kouyama Toru、Taguchi Makoto、Fukuhara Tetsuya、Takagi Masahiro、Ogohara Kazunori、Murakami Shin-ya、Peralta Javier、Limaye Sanjay S.、Imamura Takeshi、Nakamura Masato、Sato Takao M.、Satoh Takehiko
  • Journal Title: Science Volume: 368 Issue: 6489 Pages: 405-409
  • DOI: 10.1126/science.aaz4439
  • NAID: 120006863171
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations (2020)
  • Author(s): Sato T.M.、Satoh T.、Sagawa H.、Manago N.、Lee Y.J.、Murakami S.、Ogohara K.、Hashimoto G.L.、Kasaba Y.、Yamazaki A.、Yamada M.、Watanabe S.、Imamura T.、Nakamura M.
  • Journal Title: Icarus Volume: 345 Pages: 113682-113682
  • DOI: 10.1016/j.icarus.2020.113682
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Global Structure of Thermal Tides in the Upper Cloud Layer of Venus Revealed by LIR on Board Akatsuki (2019)
  • Author(s): Kouyama T.、Taguchi M.、Fukuhara T.、Imamura T.、Horinouchi T.、Sato T. M.、Murakami S.、Hashimoto G. L.、Lee Y. J.、Futaguchi M.、Yamada T.、Akiba M.、Satoh T.、Nakamura M.
  • Journal Title: Geophysical Research Letters Volume: 46 Issue: 16 Pages: 9457-9465
  • DOI: 10.1029/2019gl083820
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Constraints on Venus Lightning From Akatsuki's First 3 Years in Orbit (2019)
  • Author(s): Lorenz Ralph D.、Imai Masataka、Takahashi Yukihiro、Sato Mitsuteru、Yamazaki Atsushi、Sato Takao M.、Imamura Takeshi、Satoh Takehiko、Nakamura Masato
  • Journal Title: Geophysical Research Letters Volume: 46 Issue: 14 Pages: 7955-7961
  • DOI: 10.1029/2019gl083311
  • Peer Reviewed / Int'l Joint Research
• [Presentation] A new constraint on HCl abundance at the cloud top of Venus (2023)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: NOMAD SWT Meeting #23
  • Int'l Joint Research / Invited
• [Presentation] A new constraint on HCl abundance at the cloud top of Venus (2023)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: Venus Surface and Atmosphere Conference
  • Int'l Joint Research
• [Presentation] A new constraint on HCl abundance at the cloud top of Venus (2022)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: 第152回地球電磁気・地球惑星圏学会
• [Presentation] A new constraint on HCl abundance at the cloud top of Venus by IRTF/iSHELL observations (2022)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: Japan Geoscience Union Meeting 2022
  • Int'l Joint Research / Invited
• [Presentation] Inconsistency of HCl abundance at the cloud top of Venus between ground-based and VEX/SOIR measurements (2022)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: 第23回惑星圏研究会
• [Presentation] Retrieval of HCl abundance at the cloud top of Venus from IRTF/iSHELL spectra (2021)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: 第150回地球電磁気・地球惑星圏学会
• [Presentation] Ground-based measurements of HCl abundance at the cloud top of Venus (2021)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: Europlanet Science Congress 2021
  • Int'l Joint Research
• [Presentation] Spatial distribution of HCl abundance at the cloud top of Venus retrieved from IRTF/iSHELL spectra (2021)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: Japan Geoscience Union Meeting 2021
• [Presentation] 地球型惑星の大気化学 (2021)
  • Author(s): 佐藤隆雄
  • Organizer: 第22回惑星圏研究会
  • Invited
• [Presentation] Initial results of HCl abundance at the cloud top of Venus retrieved from IRTF/iSHELL spectra (2020)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: 第148回地球電磁気・地球惑星圏学会
• [Presentation] Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations (2020)
  • Author(s): Sato, T.M., Satoh, T., Sagawa, H., Manago, N., Lee, Y.J., Murakami, S., Ogohara, K., Hashimoto, G.L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Nakamura, M.
  • Organizer: JpGU-AGU Joint Meeting 2020
  • Int'l Joint Research
• [Presentation] High resolution 3-4 micron spectroscopy of Venus' atmosphere by IRTF/iSHELL (2020)
  • Author(s): Sato, T.M., Sagawa, H.
  • Organizer: 第21回惑星圏研究会2020
• [Presentation] Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations (2019)
  • Author(s): Sato, T.M., Satoh, T., Sagawa, H., Manago, N., Lee, Y.J., Murakami, S., Ogohara, K., Hashimoto, G.L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Nakamura, M.
  • Organizer: 第146回地球電磁気・地球惑星圏学会
• [Presentation] Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations (2019)
  • Author(s): Sato, T.M., Satoh, T., Sagawa, H., Manago, N., Lee, Y.J., Murakami, S., Ogohara, K., Hashimoto, G.L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Nakamura, M.
  • Organizer: EPSC-DPS Joint Meeting 2019
  • Int'l Joint Research
• [Presentation] Mapping of Venus' cloud top altitude from Akatsuki IR2 dayside images (2019)
  • Author(s): Sato, T.M., Satoh, T., Sagawa, H., Manago, N., Lee, Y.J., Murakami, S., Ogohara, K., Hashimoto, G.L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Nakamura, M.
  • Organizer: International Venus Conference 2019
  • Int'l Joint Research
• [Presentation] Cloud top structure of Venus retrieved from the Akatsuki IR2 dayside observations (2019)
  • Author(s): Sato, T.M., Satoh, T., Sagawa, H., Manago, N., Lee, Y.J., Murakami, S., Ogohara, K., Hashimoto, G.L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Nakamura, M.
  • Organizer: Japan Geoscience Union Meeting 2019
  • Int'l Joint Research / Invited