IMPROVED SURFACE AND BOUNDARY-LAYER MODELS FOR THE GODDARD-INSTITUTE-FOR-SPACE-STUDIES GENERAL-CIRCULATION MODEL

Improved surface and boundary layer models have been developed and imp lemented in the Goddard Institute for Space Studies (GISS) general cir culation model (GCM). The new boundary layer model retains the methodo logy of the Model 2 version in which the surface winds are interpolate d using a model profile but amends the approximations that were previo usly used to keep the model analytical for ease of computation. The ne w surface layer model is entirely different than that previously used in the GISS GCM and uses similarity theory to compute the transport co efficients, drag coefficient, Dalton number, and Stanton number. The c ombination yields distinct improvements in the general circulation cha racteristics of the GISS GCM. The new boundary layer and surface model s were chosen to allow surface properties to be precomputed, resulting in minimal impact to the overall execution time. This is particularly important in a GCM used for climate experiments with timescales spann ing centuries.