A Numerical Model of a Diurnally Varying Tropical Cloud Cluster Disturbance

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Abstract
A numerical model of the tropical cloud cluster disturbance is presented. The model is constructed and verified from the detailed results obtained by compositing many radiosonde reports from the tropical west Pacific. The model is based on the so-called “primitive equations” in the axisymmetric form. The top and bottom model layers simulate the relevant characteristics of the stratosphere and boundary layer. Warming by diabatic processes is determined diagnostically for a quasi-steady disturbance. Differences in convective and radiative heating between the disturbance and its environment emphasize the equal role of convective and radiative heating in maintaining the disturbance. Divergence profiles and rainfall rates obtained by specifying the radiative heating with a time-dependent analytic expression compare very well with available data. The physical link between the time-dependent radiative heating and the resulting atmospheric response is discussed.

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