An Energy Balance Model Based on Potential Vorticity Homogenization

Abstract

It has long been suggested that the extratropical eddies originating in baroclinic instability act to neutralize the atmosphere with respect to baroclinic instability. These studies focused on the Charney?Stern condition for stability, and since the implication of this condition was the elimination of meridional temperature gradients at the surface, contrary to observations, there appeared little possibility that the hypothesis was correct. However, Lindzen found that potential vorticity (PV) mixing along isentropic surfaces accompanied by elevated tropopause height and/or reduced jet width could also lead to baroclinic neutralization. Since it is not obvious what implications such a neutral state would have for meridional structure of wind and especially temperature, the authors examine, as a first step, in this paper the implications of an assumed fixed PV gradient in the extratropical troposphere. It is shown that this assumption, combined with an assumption of a moist adiabatic temperature structure in the Tropics, a constraint on surface static stability, and overall radiative equilibrium, suffices to constrain a model earth?s zonal mean climate. Comparison of the model climate with the observed climate, and variation of certain of the model?s assumptions to resolve differences, allow the authors to consider the role of deep convection in the climate of the midlatitudes, to investigate the connection between surface turbulent heat fluxes and meridional energy fluxes carried by baroclinic eddies, and to deduce the role of the stratosphere?s overturning circulation in determining the height of the tropopause.