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The first assimilation of Akatsuki single-layer winds and its validation with Venusian atmospheric waves excited by solar heating. Sci Rep 2022; 12:14577. [PMID: 36028537 PMCID: PMC9418169 DOI: 10.1038/s41598-022-18634-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Accepted: 08/16/2022] [Indexed: 11/08/2022] Open
Abstract
The planetary missions including the Venus Climate Orbiter 'Akatsuki' provide new information on various atmospheric phenomena. Nevertheless, it is difficult to elucidate their three-dimensional structures globally and continuously only from observations because satellite observations are considerably limited in time and space. We constructed the first 'objective analysis' of Venus' atmosphere by assimilating cloud-top horizontal winds on the dayside from the equator to mid-latitudes, which is frequently obtained from Akatsuki's Ultraviolet Imager (UVI). The three-dimensional structures of thermal tides, found recently to play a crucial role in maintaining the super rotation, are greatly improved by the data assimilation. This result is confirmed by comparison with Akatsuki's temperature observations. The momentum transport caused by the thermal tides and other disturbances are also modified by the wind assimilation and agrees well with those estimated from the UVI observations. The assimilated dataset is reliable and will be open to the public along with the Akatsuki observations for further investigation of Venus' atmospheric phenomena.
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Amateur Observers Witness the Return of Venus’ Cloud Discontinuity. ATMOSPHERE 2022. [DOI: 10.3390/atmos13020348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Firstly identified in images from JAXA’s orbiter Akatsuki, the cloud discontinuity of Venus is a planetary-scale phenomenon known to be recurrent since, at least, the 1980s. Interpreted as a new type of Kelvin wave, this disruption is associated to dramatic changes in the clouds’ opacity and distribution of aerosols, and it may constitute a critical piece for our understanding of the thermal balance and atmospheric circulation of Venus. Here, we report its reappearance on the dayside middle clouds four years after its last detection with Akatsuki/IR1, and for the first time, we characterize its main properties using exclusively near-infrared images from amateur observations. In agreement with previous reports, the discontinuity exhibited temporal variations in its zonal speed, orientation, length, and its effect over the clouds’ albedo during the 2019/2020 eastern elongation. Finally, a comparison with simultaneous observations by Akatsuki UVI and LIR confirmed that the discontinuity is not visible on the upper clouds’ albedo or thermal emission, while zonal speeds are slower than winds at the clouds’ top and faster than at the middle clouds, evidencing that this Kelvin wave might be transporting momentum up to upper clouds.
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Fukuya K, Imamura T, Taguchi M, Fukuhara T, Kouyama T, Horinouchi T, Peralta J, Futaguchi M, Yamada T, Sato TM, Yamazaki A, Murakami SY, Satoh T, Takagi M, Nakamura M. The nightside cloud-top circulation of the atmosphere of Venus. Nature 2021; 595:511-515. [PMID: 34290430 DOI: 10.1038/s41586-021-03636-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 05/12/2021] [Indexed: 11/09/2022]
Abstract
Although Venus is a terrestrial planet similar to Earth, its atmospheric circulation is much different and poorly characterized1. Winds at the cloud top have been measured predominantly on the dayside. Prominent poleward drifts have been observed with dayside cloud tracking and interpreted to be caused by thermal tides and a Hadley circulation2-4; however, the lack of nightside measurements over broad latitudes has prevented the unambiguous characterization of these components. Here we obtain cloud-tracked winds at all local times using thermal infrared images taken by the Venus orbiter Akatsuki, which is sensitive to an altitude of about 65 kilometres5. Prominent equatorward flows are found on the nightside, resulting in null meridional velocities when these are zonally averaged. The velocity structure of the thermal tides was determined without the influence of the Hadley circulation. The semidiurnal tide was found to have an amplitude large enough to contribute to the maintenance of the atmospheric superrotation. The weakness of the mean meridional flow at the cloud top implies that the poleward branch of the Hadley circulation exists above the cloud top and that the equatorward branch exists in the clouds. Our results should shed light on atmospheric superrotation in other celestial bodies.
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Affiliation(s)
- Kiichi Fukuya
- Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
| | - Takeshi Imamura
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan.
| | | | | | - Toru Kouyama
- Digital Architecture Research Center, National Institute of Advanced Industrial Science and Technology, Tokyo, Japan
| | - Takeshi Horinouchi
- Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
| | - Javier Peralta
- Instituto de Astrofísica e Ciências do Espaço, Lisbon, Portugal.,Colegio Huerta de la Cruz, Algeciras, Spain
| | | | | | - Takao M Sato
- Space Information Center, Hokkaido Information University, Ebetsu, Japan
| | - Atsushi Yamazaki
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
| | - Shin-Ya Murakami
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
| | - Takehiko Satoh
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
| | | | - Masato Nakamura
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
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4
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Sugimoto N, Fujisawa Y, Kashimura H, Noguchi K, Kuroda T, Takagi M, Hayashi YY. Generation of gravity waves from thermal tides in the Venus atmosphere. Nat Commun 2021; 12:3682. [PMID: 34140504 PMCID: PMC8211692 DOI: 10.1038/s41467-021-24002-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 05/31/2021] [Indexed: 02/05/2023] Open
Abstract
Gravity waves play essential roles in the terrestrial atmosphere because they propagate far from source regions and transport momentum and energy globally. Gravity waves are also observed in the Venus atmosphere, but their characteristics have been poorly understood. Here we demonstrate activities of small-scale gravity waves using a high-resolution Venus general circulation model with less than 20 and 0.25 km in the horizontal and vertical grid intervals, respectively. We find spontaneous gravity wave radiation from nearly balanced flows. In the upper cloud layer (~70 km), the thermal tides in the super-rotation are primary sources of small-scale gravity waves in the low-latitudes. Baroclinic/barotropic waves are also essential sources in the mid- and high-latitudes. The small-scale gravity waves affect the three-dimensional structure of the super-rotation and contribute to material mixing through their breaking processes. They propagate vertically and transport momentum globally, which decelerates the super-rotation in the upper cloud layer (~70 km) and accelerates it above ~80 km.
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Affiliation(s)
- Norihiko Sugimoto
- grid.26091.3c0000 0004 1936 9959Department of Physics, Keio University, Yokohama, Japan ,grid.26091.3c0000 0004 1936 9959Research and Education Center for Natural Sciences, Keio University, Yokohama, Japan
| | - Yukiko Fujisawa
- grid.26091.3c0000 0004 1936 9959Research and Education Center for Natural Sciences, Keio University, Yokohama, Japan
| | - Hiroki Kashimura
- grid.31432.370000 0001 1092 3077Department of Planetology, Kobe University, Kobe, Japan ,grid.31432.370000 0001 1092 3077Center for Planetary Science, Kobe University, Kobe, Japan
| | - Katsuyuki Noguchi
- grid.174568.90000 0001 0059 3836Faculty of Science, Nara Women’s University, Nara, Japan
| | - Takeshi Kuroda
- grid.69566.3a0000 0001 2248 6943Department of Geophysics, Tohoku University, Sendai, Japan
| | - Masahiro Takagi
- grid.258798.90000 0001 0674 6688Faculty of Science, Kyoto Sangyo University, Kyoto, Japan
| | - Yoshi-Yuki Hayashi
- grid.31432.370000 0001 1092 3077Department of Planetology, Kobe University, Kobe, Japan ,grid.31432.370000 0001 1092 3077Center for Planetary Science, Kobe University, Kobe, Japan
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Yamamoto M, Ikeda K, Takahashi M. Atmospheric response to high-resolution topographical and radiative forcings in a general circulation model of Venus: Time-mean structures of waves and variances. ICARUS 2021; 355:114154. [PMID: 33052146 PMCID: PMC7545273 DOI: 10.1016/j.icarus.2020.114154] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 09/28/2020] [Accepted: 10/05/2020] [Indexed: 06/11/2023]
Abstract
Thermal tides, stationary waves, and general circulation are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography, based on time average analysis. The simulated wind and static stability are very similar to the observed ones (e.g., Horinouchi et al., 2018; Ando et al., 2020). The simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m s-1 around the cloud-heating maximum (~65 km). The zonal-flow acceleration rates of 0.2-0.5 m s-1 Earth day-1 are produced by both horizontal and vertical momentum fluxes at low latitudes. In the GCM simulation, strong solar heating above the cloud top (>69 km) and infrared heating around the cloud bottom (~50 km) modify the vertical structures of thermal tides and their vertical momentum fluxes, which accelerate zonal flow at 103 Pa (~75 km) and 104 Pa (~65 km) at the equator and around 103 Pa at high latitudes. Below and in the cloud layer, surface topography weakens the zonal-mean zonal flow over the Aphrodite Terra and Maxwell Montes, whereas it enhances the zonal flow in the southern polar region. The high-resolution topography produces stationary fine-scale bow structures at the cloud top and locally modifies the variances in the geographical coordinates (i.e., the activity of unsteady wave components). Over the high mountains, vertical spikes of the vertical wind variance are found, indicating penetrative plumes and gravity waves. Negative momentum flux is also locally enhanced at the cloud top over the equatorial high mountains. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the nightside than on the dayside at the cloud top. Strong dependences of the eddy heat and momentum fluxes on local time are predominant. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves.
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Affiliation(s)
- Masaru Yamamoto
- Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
| | - Kohei Ikeda
- National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan
| | - Masaaki Takahashi
- National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan
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Affiliation(s)
- Sebastien Lebonnois
- Laboratoire de Météorologie Dynamique (LMD/IPSL), Sorbonne Université, ENS, PSL Research University, Ecole Polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France.
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