This project will test the possibility that bulk parameterizations of boundary layer processes are adequate to resolve air-surface interactions in general circulation models. This possibility will be tested by comparing results from a global forecast model, with explicitly resolved surface to atmosphere transfer, to the bulk flux approximations similar to those used in the Community Climate Model of the National Center for Atmospheric Research. The tests will emphasize boundary layer flows that flank the South American Andes Mountain ranges. This work may lead to improved and efficient modelling of climate processes in which air-surface interchanges are of principal importance.