The surface flow in a statistical climate model - a test of a parameterization of large-scale momentum fluxes

Abstract

Green's parameterization of the latitudinal flux of zonal momentum by large-scale eddies is investigated. In a steady-state, β-plane model of the zonal mean troposphere a simple basis for estimating transfer coefficients (eddy diffusivities) leads to a satisfactory representation of this large-scale momentum flux, as indicated by the surface zonal flow. the simple basis appears inappropriate for systems in which the β-effect is not dominant. In a spherical polar, quasi-geostrophic model of the zonal mean troposphere an adaptation of the method leads to less satisfactory results. It is clear that the spatial variation of the transfer coefficients is more important than in the β-plane case; and a more precise way of estimating this variation is desirable. Barotropic/baroclinic stability analyses seem likely to provide the most reliable basis, but their use would amount to an essentially different parameterization technique: less elaborate methods may be adequate.