Research over the past decade has demonstrated that sub-grid scale spatial heterogeneities in soil moisture, precipitation, and vegetation cover have substantial effects in determining surface evapotranspiration, runoff, and other surface properties coupled to atmospheric climate. Many of these processes occur on spatial scales too fine to be resolved by most current climate models. This paper will present the development and preliminary sensitivity studies of a high-resolution, fine-mesh global model (CCM3/HRBATS) for these processes.
The first of these sensitivity experiments includes a simple dissagregation scheme for rainfall in the Amazon region. Results from this simulation suggest that there is a close relationship between the diurnal cycle of rainfall at a particular point, and the spatial distribution of convective rainfall around it. Land-surface schemes that include spatial precipitation distribution, either explicitly or as a fractional area where rainfall is occurring, appear to produce a different model-simulated diurnal cycle of precipitation than those who do not. Differences in the simulations between theses schemes extend upward from the surface into the boundary layer. Current available datasets for Amazonia (ABRACOS, ABLE, RBLE, FLUAMAZON, etc.) and satellite observations (ISCCP) are used to validate the behavior of these models through the diurnal cycle.