Dynamics of Venus' superrotation: The eddy momentum transport processes newly found in a GCM

Yamamoto, Masaru; Takahashi, Masaaki

doi:10.1029/2004gl019518

Cited by 52 publications

(45 citation statements)

References 16 publications

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“…Yamamoto and Takahashi (2003a (hereinafter, YT), 2003b) reproduced super-rotation by Venus-like AGCM that incorporates the Venus rotation rate, high surface pressure, high surface temperature, and zonally uniform solar heating; their results support the Gierasch mechanism. Yamamoto and Takahashi (2004) extend these works by adopting three-dimensional solar heating and reproduced super-rotation; their result also supports the Gierasch mechanism. Takagi and Matsuda (2007) reproduced super-rotation using a nonlinear dynamical model on a sphere that has Venusian parameters and the only tidal component for the sola heating; their results suggest that a vertically propagating thermal tide can reproduce superrotation.…”

Section: Introductionsupporting

confidence: 57%

Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

Kido

Wakata

2008

Journal of the Meteorological Society of Japan

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969 IntroductionVenus has a thick CO 2 atmosphere with surface pressure of 9.2 × 10 4 hPa. The surface temperature is about 730 K because of the greenhouse effect imparted by thick CO 2 gas. Sulfuric acid clouds blanket the entire planet at about 47−70 km. An important characteristic of Venus is its very slow rotation: its rotation period is 243 earth days. One Venus Solar day is 117 days considering both daily rotation and revolution. It might therefore be speculated that convection between dayside and nightside dominates the atmospheric circulation, and that the convection pattern moves slowly together with slowly migrating subsolar and antisolar points. However, such a convection has not been observed, and observations have confirmed that fast zonal winds, called super-rotation or four-day circulation, are predominant. The Venusian cloud pattern rotates in the same direction as the rotation of the solid Venus with about four days around Venus along the equator. The zonal wind speed increases with height; its velocity is about 100 m s −1 at the cloud top level (about 70 km). The wind is 60 times faster than the solid planet. The reason why dayside-nightside circulation does not appear but super-rotation (four-day circulation) is dominant remains still unclear. Furthermore, the mechanism producing and maintaining such a fast zonal wind Japan, Vol. 86, No. 6, pp. 969−979, 2008 Journal of the Meteorological Society of AbstractWe investigated the existence of multiple equilibrium states in the Venusian atmospheric general circulation suggested by Matsuda (1980Matsuda ( , 1982 using a Venus-like atmospheric general circulation model. We ran the model from two initial conditions: a state with large zonal wind increasing with height and a motionless state. For the large zonal wind initial state, a strong zonal wind with weak meridional circulation, i.e., super-rotation, appears. However for the motionless initial condition, slow zonal wind with strong meridional circulation relative to the farmer state appears. Each circulation reached a quasi-steady state. These results have the same features suggested by Matsuda. The presence of multiple equilibrium states was sensitive to the horizontal eddy viscosity parameter. For the strong zonal wind state, the acceleration of the zonal mean zonal wind results from the horizontal EP flux divergence from the wavenumber one component on the equator, which is mainly maintained by the Gierasch mechanism (1975). The presence of multiple equilibrium states suggests that an alternative slow zonal wind state could appear in the Venusian atmosphere if an appropriate initial condition or drastic fluctuation is assigned.

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Section: Introductionsupporting

confidence: 57%

Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

Kido

Wakata

2008

Journal of the Meteorological Society of Japan

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“…To explain the generation and maintenance mechanism of the Venusian atmospheric super-rotation, several mechanisms based on thermal tides, meridional circulation, or SS-AS circulation have been proposed (Schubert and Whitehead 1969;Thompson 1970;Fels and Lindzen 1974;Gierasch 1975;Matsuda 1980). Recent numerical studies suggest that both the thermal tide (e.g., Matsuda 2006, 2007) and meridional circulation mechanisms (e.g., Yamamoto and Takahashi 2004) might be viable in the Venusian atmosphere, in which the vertical and horizontal transport of angular momentum due to thermal tides, eddies, and mean meridional circulation plays an important role. Other kinds of waves, such as the four-and fiveday waves found in UV images of the cloud top (e.g., Del Kouyama et al 2013Kouyama et al , 2015 and small-scale disturbances suspected to be related to gravity waves (e.g., Sagdeev et al 1986;Hinson and Jenkins 1995;Peralta et al 2008;Garcia et al 2009) may also play important roles in the establishment and maintenance of the atmosphere's super-rotation.…”

Section: Introductionmentioning

confidence: 99%

Overview of Akatsuki data products: definition of data levels, method and accuracy of geometric correction

Ogohara

Takagi

Murakami

et al. 2017

Earth Planets Space

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We provide an overview of data products from observations by the Japanese Venus Climate Orbiter, Akatsuki, and describe the definition and content of each data-processing level. Levels 1 and 2 consist of non-calibrated and calibrated radiance (or brightness temperature), respectively, as well as geometry information (e.g., illumination angles). Level 3 data are global-grid data in the regular longitude-latitude coordinate system, produced from the contents of Level 2. Non-negligible errors in navigational data and instrumental alignment can result in serious errors in the geometry calculations. Such errors cause mismapping of the data and lead to inconsistencies between radiances and illumination angles, along with errors in cloud-motion vectors. Thus, we carefully correct the boresight pointing of each camera by fitting an ellipse to the observed Venusian limb to provide improved longitude-latitude maps for Level 3 products, if possible. The accuracy of the pointing correction is also estimated statistically by simulating observed limb distributions. The results show that our algorithm successfully corrects instrumental pointing and will enable a variety of studies on the Venusian atmosphere using Akatsuki data.

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“…Since the heating distribution depends on the zenith angle, it is strongly related to the oblique angle of the planetary rotation axis. The equator-pole contrast of the surface potential temperature is set at 10 K (Joshi & Young 2002;Yamamoto & Takahashi 2004, 2006. The experimental conditions (the planetary rotation period T Ω , the solar day T solar , the orbital period T orbit ) are summarized in Table 1.…”

Section: Modelmentioning

confidence: 99%

Prograde and retrograde atmospheric rotation of cloud-covered terrestrial planets

Yamamoto¹,

Takahashi²

2008

A&A

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Context. Cloud-covered middle-atmospheric dynamics are important in the strong prograde rotation (i.e. superrotation) observed in some terrestrial-planet atmospheres, such as Venus and Titan. In addition, the unified theory and the mechanism driving the general circulation could be extended to as yet unknown extrasolar Earth-sized habitable planet atmospheres. Aims. We elucidate the dynamical process controlling prograde and retrograde atmospheric rotation induced by cloud heating in the middle atmosphere of terrestrial planets. Methods. The terrestrial middle-atmospheric circulation is examined using a general circulation model in which astronomical parameters are varied. Results. Middle-atmospheric circulation is strongly controlled by seasonal variation of the meridional circulation. Prograde and retrograde atmospheric rotation is determined by the direction of vertical angular momentum transport due to the meridional circulation resulting from tilting of the planetary rotation axis. The retrograde rotation rate is limited to −Ω for slowly rotating planets (where Ω is the planetary rotation rate).

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Dynamics of Venus' superrotation: The eddy momentum transport processes newly found in a GCM

Cited by 52 publications

References 16 publications

Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

Overview of Akatsuki data products: definition of data levels, method and accuracy of geometric correction

Prograde and retrograde atmospheric rotation of cloud-covered terrestrial planets

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