A Comparison of Simple and Complex Treatments of Surface Hydrology and Thermodynamics Suitable for Mesoscale Atmospheric Models

Abstract

Alternative treatments of the hydrologic and thermodynamic processes at the earth's surface within a mesoscale model are discussed in this study. Specifically, the question of under what circumstances it is necessary to use a complex surface parameterization scheme as opposed to simpler ones is addressed. Three versions of a one-dimensional planetary boundary layer model were employed, where the primary differences among them are in their surface modules. One uses a simple treatment of the surface characteristics (time independent). In another, the surface processes are represented by a complex surface physics-soil hydrology scheme, while the third one is similar to the first one but the moisture-availability parameter has a specified temporal variation during and after a precipitation event. Several numerical simulations were performed. They showed that the models? solutions differ the most when the vegetation cover and the surface net radiative flux are large, and the soil-water content cannot satisfy the evapotranspiration demand. When a precipitation event is present during the simulation period, the largest differences are apparent when the preprecipitation surface evapotranspiration is restricted and the precipitation event occurs in the morning. The simulations also showed that the upgraded simple scheme can sometimes represent a satisfactory substitute for the simple scheme when a precipitation event is present during the simulation period.