Cloud layers

The VIRTIS apparatus (Visible Infrared Thermal Imaging Spectrometer) on board can observe the atmosphere and the cloud layers at various depths (on both the day and the night side of the planet). VIRTIS has also provided data for the first temperature map of the hot Venusian surface. These data have led to the identification of hot spots and thus provided evidence for possible volcanic activity (www.esa.int/specials/venusexpress). 

Uranus The temperature in the Uranus atmosphere, which consists of molecular hydrogen containing around 12% helium, is close to 60 K. A methane cloud layer has been detected in the lower layers of this atmosphere. The planet is surrounded by a magnetosphere which extends into space for about ten times the diameter of Uranus. The planet has 27 moons of various sizes and is surrounded by a ring system which consists of thin dark rings. The planet is unusual in two respects its tilted axis and retrograde rotation. 

Dry air rising in the atmosphere has to expand as the pressure in the atmosphere decreases. This pV work decreases the temperature in a regular way, known as the adiabatic lapse rate, Td, which for the Earth is of order 9.8 Kkm-1. As the temperature decreases, condensable vapours begin to form and the work required for the expansion is used up in the latent heat of condensation of the vapour. In this case, the lapse rate for a condensable vapour, the saturated adiabatic lapse rate, is different. At a specific altitude the environmental lapse rate for a given parcel of air with a given humidity reaches a temperature that is the same as the saturated adiabatic lapse rate, when water condenses and clouds form Clouds in turn affect the albedo and the effective temperature of the planet. Convection of hot, wet (containing condensable vapour) air produces weather and precipitation. This initiates the water cycle in the atmosphere. Similar calculations may be performed for all gases, and cloud layers may be predicted in all atmospheres. 

Dust Minimum ignition temperature CC) cloud layer Minimum explosible concentration (g/D... 

The radiative transfer model in Madronich (1987) permits the proper treatment of several cloud layers, each with height-dependent liquid water contents. The extinction coefficient of cloud water is parameterized as a function of the cloud water computed by the three-dimensional model based on a parametrization given by Slingo (1989). For the Madronich scheme used in WRF/Chem, the effective radius of the cloud droplets follows Jones et al. (1994). For aerosol particles, a constant extinction profile with an optical depth of 0.2 is applied. 

The most prominent feature of Venus middle atmosphere is the global cloud layer that begins at 45 km altitude and extends to 70 km altimde, with thinner hazes 20 km above and below these altitudes. Venus appears yellow-white in visible light, but the first UV images of Venus in the 1920s showed dark or tC-shaped cloud features. The... 

All of the clouds are low density, because the visibility inside the densest region of the clouds is a few kilometers. The average and maximum optical depths (t) in visible light of all cloud layers are 29 and 40, respectively, versus average and maximum t values of 6 and 350 for terrestrial clouds. Average mass densities for Venus clouds are 0.01-0.02 g m versus an average mass density of 0.1-0.5 g m for fog clouds on Earth. Venus cloud layers are typically divided into the subcloud haze (32-48 km), the lower cloud (48-51 km), middle cloud (51-57 km), upper cloud (57-70 km), and upper haze (70-90 km). 

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