Parameterization of dynamical subgrid-scale processes in a spectral GCM

Abstract

Global atmospheric analyses from several sources are used to infer the dynamical effects of smaller horizontal scales on larger horizontal scales for the purpose of parameterizing these interactions in general circulation models. The nonlinear interactions among scales are calculated in terms of a spectral decomposition on the sphere. A spectral empirical interaction function (EIF) is obtained from data that, when applied to larger scales (corresponding to resolved scales in a numerical model), recoveres the effects of small scales (corresponding to unresolved, subgrid scales in a numerical model) on these larger scales in the data. The effect of the EIF on the simulated climate of the Canadian Climate Centre General Circulation Model is investigated as is a simulation with a restricted version of the function, for which the negative values are set to zero. As expected, the results obtained using the full empirical function show increased levels of kinetic energy at relatively small wave numbers, where models have often been deficient. -from Authors