Parameterization of the Planetary Boundary Layer in Atmospheric General Circulation Models

Numerical general circulation models (GCMs) have been adopted as important tools for understanding the physical basis of climatic changes. These models vary greatly, especially in their treatment of those physical processes that cannot be resolved by the grid spacing of the model, such as boundary-layer processes. There are several approaches to boundary-layer parameterization: some of these are based on so-called K-theory; others are based on similarity theory. Considering the varying degrees of vertical resolution of general circulation models, determination of the surface fluxes is perhaps the most important aspect of the boundary-layer parameterization in a GCM. At present there is not sufficient evidence to determine which particular boundary-layer parameterization scheme is most satisfactory. It is therefore suggested that a systematic sensitivity test of various schemes be carried out to determine the best approach.