Baroclinic Adjustment and Midlatitude Temperature Profiles

Abstract

An assessment is made of how baroclinically unstable waves might stabilize a zonal mean Bow by adjusting vertical temperature profiles. To this end, temperature profiles for a continuous atmosphere an derived which are baroclinically stable. Features of these profiles of relevance to the atmosphere are discussed, and a requirement is derived for the minimal amount of profile adjustment necessary to stabilize the zonal mean flow. Neither the atmosphere nor realistic models can perform the profile adjustment necessary to attain a rigorously stable state, but a model used here which includes vertical heat fluxes from baroclinically unstable waves can attain an effectively stable state that is very similar to the rigorously stable state. Observed temperature profiles, as well as model profiles that are not effectively stable, also display features of the adjusted profiles, indicating that much of the temperature variation with height in the midlatitude troposphere can be understood in terms of the adjustment. The model results also show that vertical eddy heat fluxes arising from baroclinic instability try to produce the adjustment to a stable state but other processes, most notably those controlling temperature near the surface, prevent the fluxes from being successful. Finally, the model results are used to show similarities between the continuous atmosphere adjustment presented here and the two-layer atmosphere adjustment studied by others. The work presented here suggests that vertical heat fluxes from baroclinically unstable waves can produce significant variations of midlatitude lapse rates in both height and time; midlatitude models that omit these variations may be missing an important aspect of wave-mean flow interaction.