VERTICAL EDDY HEAT FLUXES AND THE TEMPERATURE STRUCTURE OF THE MID-LATITUDE TROPOSPHERE by WILLIAM

A study of the interaction between vertical eddy heat fluxes and the vertical temperature structure of the mid-latitude troposphere is presented, guided by the hypothesis that a tendency of baroclinically unstable eddies to stabilize the zonal mean flow should be visible in the observed time-averaged zonal mean flow, the baroclinic adjustment hypothesis. Vertical temperature profiles in a continuous atmosphere are derived for which the zonal mean flow is stable, using the Charney and Stern theorem. The strictly stable profiles cannot occur in the atmosphere, but an atmospheric profile similar to the strictly stable profile might be realizable. It is hypothesized that in such a case, the atmospheric profile would be effectively stable, the profile's instability being so weak that other processes would prevent the instability from manifesting itself. The observed atmosphere does display features of the vertical temperature structure adjustment. A scaling analysis of the zonally-averaged, quasi-Boussinesq thermodynamic equation using scales for eddy fluxes suggested by studies of linear baroclinic instability and by observations shows that the heating by the vertical eddy heat flux can be as important as that produced by the meridional eddy heat flux. This result occurs because the important length scales for eddy fluxes in the zonally-averaged thermodynamic equation are the scales of the flux divergences, not the scales of the eddy oscillations. The analysis shows how averaging operators may alter the relative sizes of terms in an equation so that terms considered unimportant before averaging can become important after averaging. A heating balance model for the vertical temperature structure is developed, motivated by the scaling analysis and by the work of others. The model computes an equilibrium among the heating rates by simplified representations of the vertical eddy heat flux, moist convection, and radiation. Model equilibrium states fall into two categories based on their temperature structures. In one, the eddy fluxes play an important role in determining the vertical temperature structure, and the temperature structure displays evidence of the eddy flux's tendency to adjust the flow to stability. In the other, the eddy flux has much less influence, and the temperature structures tend to resemble that of the model's radiative-convective equilibrium, where the eddy heating is absent. The most unstable wave tends to be the wave causing the greatest stabilization of the zonal mean flow. Model runs which neglect all physical processes contained in the full model except the eddy-mean