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central dense overcast
The central dense overcast, or CDO, of a tropical cyclone or strong subtropical cyclone is the large central area of thunderstorms surrounding its circulation center, caused by the formation of its eye wall. It can be round, angular, oval, or irregular in shape. This feature shows up in tropical cyclones of tropical storm or hurricane strength. How far the center is embedded within the CDO, and the temperature difference between the cloud tops within the CDO and the cyclone's eye, can help determine a tropical cyclone's intensity. Locating the center within the CDO can be a problem for strong tropical storms and with systems of minimal hurricane strength as its location can be obscured by the CDO's high cloud canopy. This center location problem can be resolved through the use of microwave satellite imagery.
After a cyclone reaches hurricane intensity, an eye appears at the center of the CDO, defining its center of low pressure and its cyclonic wind field. Tropical cyclones with changing intensity have more lightning within their CDO than steady state storms. Tracking cloud features within the CDO, using frequently updated satellite imagery, can also be used to determine its intensity. The highest maximum sustained winds within a tropical cyclone, as well as its heaviest rainfall, are usually located under the coldest cloud tops in the CDO.
==Characteristics==
It is a large region of thunderstorms surrounding the center of stronger tropical and subtropical cyclones which shows up brightly (with cold cloud tops) on satellite imagery. The CDO forms due to the development of an eyewall within a tropical cyclone. Its shape can be round, oval, angular, or irregular. Its development can be preceded by a narrow, dense, C-shaped convective band. Early in its development, the CDO is often angular or oval in shape, which rounds out, increases in size, and appears more smooth as a tropical cyclone intensifies. Rounder CDO shapes occur in environments with low levels of vertical wind shear.〔
The strongest winds within tropical cyclones tend to be located under the deepest convection within the CDO, which is seen on satellite imagery as the coldest cloud tops.〔 The radius of maximum wind is usually collocated with the coldest cloud tops within the CDO, which is also the area where a tropical cyclone's rainfall reaches its maximum intensity. For mature tropical cyclones that are steady state, the CDO contains nearly no lightning activity, though lightning is more common within weaker tropical cyclones and for systems fluctuating in intensity.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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