On the simulation of the axisymmetric circulation of the atmosphere

Abstract

The paper describes a zonally averaged model of the atmospheric state in which the effects of the eddies on the zonal state are parameterized in terms of exchange coefficients which vary with latitude and time in the most general model. In comparison with earlier investigations this model contains a more detailed description of the atmospheric heat budget and a more general description of the exchange mechanisms. However, the basic model is still a quasi-geostrophic, two-level representation of the large-scale flow. Two experiments have been carried out. Both of them simulate the seasonal variation of the zonally averaged state of the atmosphere. The first experiment uses diagnostically determined exchange coefficients which are based on an observational study and which depend upon latitude only. The second experiment employs exchange coefficients which vary with latitude and time. In addition, the magnitude and the functional dependence on latitude are determined by the model parameters at any given time. The results show that a considerably improved simulation of the zonally-averaged state is obtained by a better parameterization of the processes entering the heat budget as compared with earlier studies. Furthermore, the exchange coefficients which vary with latitude and time and which are, at least in part, determined by the model, result in further improvements of most features of the model. The major limitation of the model is its small vertical resolution and its quasi-geostrophic nature.