THE ROLE OF LARGE-SCALE EDDIES IN THE CLIMATE EQUILIBRIUM .1. FIXED STATIC STABILITY

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 h ow eddies arising from baroclinic instability interact with the temper ature structure. The model gives a much better simulation of the eddy momentum flux and of the total eddy forcing of the zonal-mean temperat ure and zonal wind fields than do quasigeostrophic beta-plane models. Nonetheless, the results are qualitatively similar. The midlatitude ed dy regimes range between two extreme cases. In one, the eddies have no effect on the temperature and zonal wind fields, and in the other (si milar to the observed atmosphere), the eddy forcing of the temperature and zonal wind fields is dominated by the eddy heat flux. Also, a kin d of baroclinic adjustment occurs in the regimes where eddy effects ar e strong, with the meridional temperature gradient in midlatitudes bei ng proportional to the static stability. Quantitatively some of the mo del's results differ significantly from those based on the quasigeostr ophic beta-plane. For example, the temperature structure is much more sensitive to the external forcing, and the eddy heat flux is less sens itive to the temperature structure.