Venus cloud structure and origin of UV contrast

2017 Fiscal Year Annual Research Report

• Project/Area Number: 16K17816
• Research Institution: Japan Aerospace EXploration Agency
• Principal Investigator: 佐藤 隆雄 国立研究開発法人宇宙航空研究開発機構, 宇宙科学研究所, 宇宙航空プロジェクト研究員 (50633509)
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: 金星 / 大気 / 雲 / リモートセンシング / あかつき / 地上望遠鏡観測

Outline of Annual Research Achievements

金星に存在する雲や紫外模様を形成する未知吸収物質は惑星全体の熱入力を支配しており，雲層構造や未知吸収物質の時空間変動の把握は，気候システムの理解に必要な基礎情報となる．本研究課題では，「あかつき」が取得している紫外から中間赤外にわたる撮像データと地上望遠鏡による連携観測データを用いて，金星の雲頂構造と紫外線模様起源の解明を目的としている．当該年度は下記に示す事柄について研究を行った．
「あかつき」搭載2ミクロンカメラ（IR2）の昼面画像を用いた金星雲頂構造の推定
二酸化炭素吸収帯における反射太陽光強度を観測したIR2の2.02ミクロン画像（2016年4月4日-5月25日）を用いて，放射伝達計算に基づき雲頂高度を導出する手法を考案した．雲頂は，低中緯度では比較的一様で高度70kmに位置するが，緯度45度付近を境に下降し両極域では63km付近に存在するという結果を得た．また低中緯度に広がる紫外模様に類似した微細構造の明暗は雲頂高低差で約100m程度しかないことを突き止めた．
「あかつき」搭載2ミクロンカメラ（IR2）の昼面画像を用いた金星雲頂における定在構造の特徴
雲頂高度を可視化するIR2の2.02ミクロン画像を用いて（スーパーローテーションに流されない）雲頂における定在構造を昨年度に引き続き調べた．IR2の全観測期間（2015年12月11日-2016年12月9日）で54例の定在構造を発見し，中間赤外カメラ（LIR）が発見した惑星規模の定在構造（Fukuhara et al., 2017; Kouyama et al., 2018）同様地形起源であることが分かった．一方で，より低高度の情報を有するIR2の1.73, 2.26, 2.32ミクロン画像には定在構造は存在しておらず，定在構造を引き起こす大気重力波の特性を反映していると考えられる．

Research Products

• [Journal Article] Initial products of Akatsuki 1-μm camera (2018)
  • Author(s): Iwagami, N. et al. (Sato, T.M., 28名中20番目)
  • Journal Title: Earth, Planets and Space Volume: 70 Pages: -
  • DOI: 10.1186/s40623-017-0773-5
  • Peer Reviewed / Open Access
• [Journal Article] Ultraviolet imager on Venus orbiter Akatsuki and its initial results (2018)
  • Author(s): Yamazaki, A. et al. (Sato, T.M., 26名中10番目)
  • Journal Title: Earth, Planets and Space Volume: 70 Pages: -
  • DOI: 10.1186/s40623-017-0772-6
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images (2018)
  • Author(s): Limaye, S.S. et al. (Sato, T.M., 30名中6番目)
  • Journal Title: Earth, Planets and Space Volume: 70 Pages: -
  • DOI: 10.1186/s40623-018-0789-5
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Scattering Properties of the Venusian Clouds Observed by the UV Imager on board Akatsuki (2017)
  • Author(s): Lee, Y.J., Yamazaki, A., Imamura, T., Yamada, M., Watanabe, S., Sato, T.M., Ogohara, K., Hashimoto, G.L., Murakami, S.
  • Journal Title: The Astronomical Journal Volume: 154 Pages: 44～44
  • DOI: 10.3847/1538-3881/aa78a5
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Stationary waves and slowly moving features in the night upper clouds of Venus (2017)
  • Author(s): Peralta, J., Hueso, R., Sanchez-Lavega, A., Lee, Y.J., Garcia-Munoz, A., Kouyama, T., Sagawa, H., Sato, T.M., Piccioni, G., Tellmann, S., Imamura, T., Satoh, T.
  • Journal Title: Nature Astronomy Volume: 1 Pages: 0187～0187
  • DOI: 10.1038/s41550-017-0187
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki (2017)
  • Author(s): Horinouchi, T., Murakami, S., Satoh, T., Peralta, J., Ogohara, K., Kouyama, T., Imamura, T., Kashimura, H., Limaye, S.S., Nakamura, M., Sato, T.M., Takagi, M., Watanabe, S., Yamada, M., Yamazaki, A., Young, E.F.
  • Journal Title: Nature Geoscience Volume: 10 Pages: 646～651
  • DOI: 10.1038/ngeo3016
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki (2017)
  • Author(s): Imamura, T. et al. (Sato, T.M., 39名中7番目)
  • Journal Title: Earth, Planets and Space Volume: 69 Pages: -
  • DOI: 10.1186/s40623-017-0722-3
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Absolute calibration of brightness temperature of the Venus disk observed by the Longwave Infrared Camera onboard Akatsuki (2017)
  • Author(s): Fukuhara, T. et al. (Sato, T.M., 30名中8番目)
  • Journal Title: Earth, Planets and Space Volume: 69 Pages: -
  • DOI: 10.1186/s40623-017-0727-y
  • Peer Reviewed / Open Access
• [Journal Article] Performance of Akatsuki/IR2 in Venus orbit: the first year (2017)
  • Author(s): Satoh, T. et al. (Sato, T.M., 28名中2番目)
  • Journal Title: Earth, Planets and Space Volume: 69 Pages: -
  • DOI: 10.1186/s40623-017-0736-x
  • Peer Reviewed / Open Access
• [Journal Article] Overview of Akatsuki data products: definition of data levels, method and accuracy of geometric correction (2017)
  • Author(s): Ogohara, K. et al. (Sato, T.M., 31名中18番目)
  • Journal Title: Earth, Planets and Space Volume: 69 Pages: -
  • DOI: 10.1186/s40623-017-0749-5
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Topographical and Local Time Dependence of Large Stationary Gravity Waves Observed at the Cloud Top of Venus (2017)
  • Author(s): Kouyama, T. et al. (Sato, T.M., 26名中5番目)
  • Journal Title: Geophysical Research Letters Volume: 44 Pages: 12,098～12,105
  • DOI: doi.org/10.1002/2017GL075792
  • Peer Reviewed
• [Presentation] Stationary features at the Venus cloud top seen in Akatsuki/IR2 2.02-μm dayside images (2017)
  • Author(s): Takao M. Sato, Shin-ya Murakami, Takeshi Horinouchi, Takehiko Satoh, Javier Peralta, Takeshi Imamura
  • Organizer: JpGU-AGU Joint Meeting 2017
  • Int'l Joint Research
• [Presentation] Coordinated observation of Venus cloud top with Subaru and Akatsuki (2017)
  • Author(s): Takao M. Sato, Hideo Sagawa, Toru Kouyama, Makoto Taguchi, Yeon Joo Lee, Javier Peralta, Masahiro Takagi, George Hashimoto, Takehiko Satoh, Yasumasa Kasaba, Shohei Aoki, Tetsuya Fukuhara, Atsushi Yamazaki, Takeshi Imamura, Masato Nakamura
  • Organizer: JpGU-AGU Joint Meeting 2017
  • Int'l Joint Research
• [Presentation] Venus cloud top structure seen by the coordinated Subaru and Akatsuki observations (2017)
  • Author(s): Takao M. Sato, Hideo Sagawa, Toru Kouyama, Makoto Taguchi, Yeon Joo Lee, Javier Peralta, Masahiro Takagi, George L. Hashimoto, Takehiko Satoh, Yasumasa Kasaba, Shohei Aoki, Tetsuya Fukuhara, Atsushi Yamazaki, Takeshi Imamura, Masato Nakamura
  • Organizer: European Planetary Science Congress 2017
  • Int'l Joint Research
• [Presentation] Radiative transfer modeling for analyses with Akatsuki/IR2 images (2017)
  • Author(s): Takao M. Sato, Takehiko Satoh, George L. Hashimoto, Yeon Joo Lee, Hideo Sagawa, Yasumasa Kasaba
  • Organizer: 49th Annual Division for Planerary Sceiences Meeting
  • Int'l Joint Research