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A One-Dimensional Entraining/Detraining Plume Model and Its Application in Convective Parameterization

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  • 1 Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania
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Abstract

A new one-dimensional cloud model, specifically designed for application in mesoscale convective parameterization schemes (CPSs), is introduced. The model is unique in its representation of environmental entrainment and updraft detrainment rates. In particular, the two-way exchange of mass between clouds and their environment is modulated at each vertical level by a buoyancy sorting mechanism at the interface of clear and cloudy air. The new entrainment/detrainment scheme allows vertical profiles of both updraft moisture detrainment and updraft vertical mass flux to vary in a physically realistic way as a function of the cloud-scale environment. These performance characteristics allow the parameterized vertical distribution of convective heating and drying to be much more responsive to environmental conditions than is possible with a traditional one-dimensional entraining plume model.

The sensitivities of the new model to variations in environmental convective available potential energy and vertical moisture distribution in idealized convective environments are demonstrated and its sensitivities to several key control parameters are examined. Finally, the performance of the new model in the Fritsch–Chappell CPS is evaluated. Parameterized heating and drying profiles are elucidated as they relate to the convective environment and to the type of cloud model used in the CPS.

Abstract

A new one-dimensional cloud model, specifically designed for application in mesoscale convective parameterization schemes (CPSs), is introduced. The model is unique in its representation of environmental entrainment and updraft detrainment rates. In particular, the two-way exchange of mass between clouds and their environment is modulated at each vertical level by a buoyancy sorting mechanism at the interface of clear and cloudy air. The new entrainment/detrainment scheme allows vertical profiles of both updraft moisture detrainment and updraft vertical mass flux to vary in a physically realistic way as a function of the cloud-scale environment. These performance characteristics allow the parameterized vertical distribution of convective heating and drying to be much more responsive to environmental conditions than is possible with a traditional one-dimensional entraining plume model.

The sensitivities of the new model to variations in environmental convective available potential energy and vertical moisture distribution in idealized convective environments are demonstrated and its sensitivities to several key control parameters are examined. Finally, the performance of the new model in the Fritsch–Chappell CPS is evaluated. Parameterized heating and drying profiles are elucidated as they relate to the convective environment and to the type of cloud model used in the CPS.

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