DEVELOPMENT AND TESTING OF A SURFACE FLUX AND PLANETARY BOUNDARY-LAYER MODEL FOR APPLICATION IN MESOSCALE MODELS

Although the development of soil, vegetation, and atmosphere interacti on models has been driven primarily by the need for accurate simulatio ns of long-term energy and moisture budgets in global climate models, the importance of these processes at smaller scales for short-term num erical weather prediction and air quality studies is becoming more app reciated. Planetary boundary layer (PBL) development is highly depende nt on the partitioning of the available net radiation into sensible an d latent heat fluxes. Therefore, adequate treatment of surface propert ies such as soil moisture and vegetation characteristics is essential for accurate simulation of PBL development, convective and low-level c loud processes, and the temperature and humidity of boundary layer air . In this paper, the development of a simple coupled surface and PBL m odel, which is planned for incorporation into the Pennsylvania State U niversity-National Center for Atmospheric Research Mesoscale Model(MM4 /5), is described. The soil-vegetation model is based on a simple forc e-restore algorithm with explicit soil moisture and evapotranspiration . The PBL model is a hybrid of nonlocal closure for convective conditi ons and eddy diffusion for all other conditions. A one-dimensional ver sion of the model has been applied to several case studies from field experiments in both dry desert-like conditions(Wangara) and moist vege tated conditions (First International Satellite Land Surface Climatolo gy Project Field Experiment) to demonstrate the model's ability to rea listically simulate surface fluxes as well as PBL development. This ne w surface-PBL model is currently being incorporated into the MM4-MM5 s ystem.