Some problems of Venus' atmospheric dynamics

Abstract

A brief survey is given of the observational data on wind speeds in the atmosphere of Venus, as well as results of the theory of similitude and of a scale analysis for estimation of the wind speeds and temperature contrasts. It is shown that, in the lower portion of the atmosphere, containing roughly half of the mass, the first method produces results which are in somewhat better agreement with the measurements. Measurements of the wind distribution in the atmosphere are discussed. It is shown that, in the slowly rotating atmosphere of Venus, we should expect the Solberg mechanism of inertial instability of the circulation to be effective with respect to axisymmetrical perturbations. The numerical experiments of G.P. Williams (1968, J. Atmos. Sci., 25, 34–1045; 1970, Geophys. Fluid Dyn., 1, 357–369) indicate that in this case the circulation in the meridional plane can be broken down into a series of forward and reverse cells. The existence of such cells can serve to preserve the angular momentum of the planet with its atmosphere—the total momentum of the atmospheric frictional forces against the surface should on the average equal zero. This supports the hypothesis of G. Schubert et al. (1980, J. Geophys. Res., 85, 8007–8025) concerning the multicellular structure of the meridional circulation. Data are analyzed with regard to the time variability of the circulation. If the angular momentum of Venus′ atmosphere can change by 30% (which is not excluded by the presently available data; in Earth's atmosphere seasonal variations of the momentum reach 50%), then the relative variations in the length of a Venusian day will attain 10 −3, i.e., several hours. The surface boundary layer is considered. It is shown that, due to the small transparency of the atmosphere to thermal radiation, heat transfer between the surface and the atmosphere should basically take place by turbulent heat exchange. The basic parameters of the dynamic and thermal regimes of this layer are estimated. Questions of light refraction in the boundary layer are discussed. A strict theory of refraction, developed for these conditions, confirms the preliminary rough estimates of V.I. Moroz (1976, Cosmic Res., 14, No. 5, 691–692; Space Sci. Rev., 25, 3–127), viz, that the horizon is visible on the panorama at a distance of order 100m, due to a relatively sharp negative gradient near the surface.