A General Interface between an Atmospheric General Circulation Model and Underlying Ocean and Land Surface Models: Delocalized Physics Scheme

Abstract

In order to represent in a most adequate way the various feedback mechanisms that govern the atmosphere?ocean or atmosphere?surface couplings, a ?delocalized physics? method is introduced, in which the subgrid-scale physical parameterizations of the atmospheric model are computed on a grid defined independently of the grid where adiabatic dynamics are computed. This ?physical grid,? which can be irregular and time dependent, is defined by juxtaposing the surface grids constructed independently for the ocean, land, and sea-ice models. The delocalization method allows taking into account the nonlinearities of vertical fluxes due to heterogeneities in the finescale surface properties that are not resolved by the adiabatic atmospheric dynamics calculations. The impact of delocalizing the physics to fit a given higher resolution surface grid is tested first on experiments where the global atmosphere is forced by observed ocean temperatures. The comparison demonstrates a significant improvement of the predominant variability mode of the outgoing longwave radiation field, corresponding mainly to the seasonal cycle. The delocalized physics method is then tested on an experiment where the General circulation model of the Laboratoire de Météorologie Dynamique is coupled to the Laboratoire d?Océanographie Dynamique et de Climatologie tropical Pacific ocean model. Delocalized physics allow surface fluxes to respond better to fine sea surface temperatures structures like the Legekis waves produced by the ocean model.