INTERACTIONS BETWEEN REGIONAL SURFACE FLUXES AND THE ATMOSPHERIC BOUNDARY-LAYER OVER A HETEROGENEOUS WATERSHED

The interactions between surface fluxes of sensible and latent heat and the properties of the atmospheric boundary layer (ABL) were studied for the Walnut Gulch watershed. The properties of the ABL were estimated from radiosonde measurements. Application of integrated simplified conservation equations resulted in estimates of regional fluxes that were greatly different from surface values, and often had the wrong sign. A simple modification was made to the equations, based upon the temporal changes in temperature and humidity above the ABL, assuming that such changes resulted from horizontal advection. Subsidence was assumed to be insignificant. Application of the new integrated conservation equations resulted in a dramatic improvement in the regional flux estimates. Such estimates were reasonably close to the surface measurements. Spatial variations in surface energy balance which resulted from the convective rain events affected only the properties of the lower 15 m of the atmosphere. The length scale of variations in surface moisture of about 10 km was not sufficient to affect the regional scale processes.