Surface Flux Inhomogeneities at the Southern Great Plains Cloud and Radiation Testbed Site and Their Effects on Cloud Formation

We use observations and a three-dimensional numerical model to study the effects of inhomogeneous surface fluxes on the boundary layer characteristics of a 300-km x 350-area in Oklahoma and Kansas. In particular, we consider the effects of spatially varying fluxes on the formation of boundary-layer clouds. We show that under the settled weather conditions prevailing during our case study days, the formation of boundary layer clouds was far more sensitive to spatially varying ambient meteorology than to spatially varying surface fluxes, even though surface fluxes varied significantly across the study domain. If the spatially varying surface flux values were replaced by reasonably accurate average values, then differences were readily observed, but only minor differences were found when the results were averaged over the full study domain. In light of these findings, we suggest that the importance of resolving surface fluxes in coarse resolution models such as single column models may be less than has been claimed on the basis of numerical studies and that this issue should be critically reexamined.