The Role of Large-Scale Eddies in the Climate Equilibrium. Part I: Fixed Static Stability

Abstract

An efficient two-level model on a sphere that is based on the balance equations with fixed static stability is developed and used to study how eddies arising from baroclinic instability interact with the temperature structure. The model gives a much better simulation of the eddy momentum flux and of the total eddy forcing of the zonal-mean temperature and zonal wind fields than do quasigeostrophic ?-plane models. Nonetheless, the results are qualitatively similar. The midlatitude eddy regimes range between two extreme cases. In one, the eddies have no effect on the temperature and zonal wind fields, and in the other (similar to the observed atmosphere), the eddy forcing of the temperature and zonal wind fields is dominated by the eddy beat flux. Also, a kind of baroclinic adjustment occurs in the regimes where eddy effects are strong, with the meridional temperature gradient in midlatitudes being proportional to the static stability. Quantitatively some of the model's results differ significantly from those based on the quasigeostrophic ?-plane. For example, the temperature structure is much more sensitive to the external forcing, and the eddy beat flux is less sensitive to the temperature structure.