A Mesobeta-Scale Model in Boundary-Layer Coordinates

Abstract

A mesobeta-scale numerical model is described that is designed specifically for operational use on relatively small computers (supermicro-class computers of the MicroVAX 3000/4000 type). A major aspect of the model leading to improved computational efficiency is that rather than using many model layers near the surface to resolve the growth and decay of the boundary layer explicitly, the model treats the boundary layer as a single model layer of known structure whose depth can evolve during the integration. The model equations are recant in a coordinate system, referred to as boundary-layer coordinates, based on the depth of the evolving boundary layer. The model described here does not include condensation processes, but it does include a radiation parameterization, schemes governing the structure of the stable and unstable boundary layers and the transitions between these regimes, and parameterizations for the fluxes of heat and moisture between the boundary layer and the earth's surface. Simulations have been carried out with a prototype model that has five layers and 20- km grid spacing in the fine grid mesh of its nested domain. Results of these simulations show that the model is capable of reproducing such mesoscale phenomena as mountain lee waves and the Florida sea-breeze circulation fairly well.