Alterations of the Climate of a Primitive Equation Model produced by Filtering Approximations and Subsequent Tuning and Stochastic Forcing

Abstract

The simulated climates of highly truncated nonlinear models based on the primitive equations (PE), balance equations (BE) and quasi-geostrophic (QG) equations are compared, in order to determine the effects of the filtering approximations. The models and numerical procedures are identical in all possible respects. At low forcing the QG and PE climates agree in most respects. At high forcing the QG model gives only a qualitatively correct simulation of the PE mean state and energy cycle. In contrast, the BE model is relatively successful at simulating, the PE climate. Two attempts are made to get better simulations of the PE climate within the QG framework—the tuned and perturbed QG models. The tuned QG model is better than the untuned version at simulating the PE time mean model state, but the simulated energy cycle is not improved at all. In the perturbed QG model randomly generated perturbations, designed so that their statistics are similar to the statistics of the observed prediction errors, are added to the model state at regular intervals. The perturbed QG model is nearly as successful as the BE model at simulating the PE climate.