A Method for Calculating the Effects of Deep Cumulus Convection in Numerical Models

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  • 1 Department of Atmospheric Science, State University of New York at Albany, Albany 12222
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Abstract

A closure is proposed for the b parameter of Kuo (1974), using the framework developed by Krishnamurti et al. (1976). Emphasis is placed on the time-dependent behavior of the solutions. The proposed closure is found to be the only one of several tested to produce an approach to moist neutrality in both temperature and moisture under strong external forcing. The sensitivity of the grid-scale evolution to the partitioning of moisture defined by the b parameter suggests that such partitioning must be carefully dealt with in any method for computing the effects of cumulus convection, whether or not b is explicitly present.

By including entrainment in the cloud lapse rate, the observed large-scale behavior of the vertical profile of moist static energy under disturbed conditions is simulated. The approach is shown to be easily invertible when precipitation rate is specified, thus insuring internal consistency in a model when such a procedure is used as part of a dynamic initialization.

Because it is relatively simple and general, and reproduces observed large-scale θe variations under strong forcing, the approach may be particularly suitable for large-scale models. An economical way to extend the procedure to mesoscale models is proposed.

Abstract

A closure is proposed for the b parameter of Kuo (1974), using the framework developed by Krishnamurti et al. (1976). Emphasis is placed on the time-dependent behavior of the solutions. The proposed closure is found to be the only one of several tested to produce an approach to moist neutrality in both temperature and moisture under strong external forcing. The sensitivity of the grid-scale evolution to the partitioning of moisture defined by the b parameter suggests that such partitioning must be carefully dealt with in any method for computing the effects of cumulus convection, whether or not b is explicitly present.

By including entrainment in the cloud lapse rate, the observed large-scale behavior of the vertical profile of moist static energy under disturbed conditions is simulated. The approach is shown to be easily invertible when precipitation rate is specified, thus insuring internal consistency in a model when such a procedure is used as part of a dynamic initialization.

Because it is relatively simple and general, and reproduces observed large-scale θe variations under strong forcing, the approach may be particularly suitable for large-scale models. An economical way to extend the procedure to mesoscale models is proposed.

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