The Development of an Improved Convective Initiation Scheme for Mesoscale Numerical Weather Prediction Models. Phase 1
Final rept. 1 Sep 1990-28 Feb 1991
MESOSCALE ENVIRONMENTAL SIMULATIONS AND OPERATIONS INC TROY NY
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A three-dimensional nonhydrostatic cloud model, the Terminal Area Simulation System TASS, is used to investigate the convective initiation process for an idealized case over central Florida where the forcing is provided by differential surface heating. The surface heating pattern is generated from high resolution land use data by making simple assumptions relating surface characteristics to particular land use types. The cloud model simulation produces a complicated field of both shallow and precipitating cumulus clouds. Current mesoscale parameterization schemes are evaluated for their ability to predict convective initiation. Analysis of the results show that in the first half of the run, localized differential surface sensible heating produces small areas of deep convection associated with surface features. In the latter half of the simulation, mesoscale convergence develops due to the lateral boundary conditions and provides a mesoscale organization which is well resolved by a conventional measure of mesoscale moisture convergence. Subgrid scale convergence is very well correlated with convective activity. Results suggest that the cloud model is a valuable tool for the investigation of realistic convective initiation and evolution, and that a combination of mesoscale and subgrid scale properties are necessary for successful mesoscale modeling of cumulus convection.