On the Interaction of Surface Heating Anomalies with Zonally Symmetric and Asymmetric Atmospheric Flows

Abstract

The interaction of different zonally symmetric and asymmetric flows with heating arising from a prescribed anomaly in surface temperature is investigated in linear and nonlinear quasi-geostrophic models. In cases of zonally asymmetric flows the climatic effects of changes in longitudinal position of the surface temperature anomaly with respect to the planetary wave structure are also examined. The modelled atmospheric responses to the surface temperature anomaly divide into two categories, depending upon whether the flow is baroclinically stable or unstable. For baroclinically stable flows the climatic mean atmospheric response is baroclinic in structure above the surface temperature anomaly; it is equivalent barotropic elsewhere. Maximum changes in atmospheric fields occur in the vicinity of the surface temperature anomaly in such cases. The steady-state linear model is able to predict the basic features of the nonlinear response of the baroclinically stable zonal flows, but with discrepancies in amplitude and phase. Changes in longitudinal position of the surface temperature anomaly with respect to the zonally asymmetric stable flows cause perceptible changes in atmospheric response, both above the anomaly and in other regions. Analysis of the natural variability of the model climates defined by different values of mean vertical shear and static stability of the flows confirms that most of these changes in response arc statistically significant. For baroclinically unstable flows the changes in climatic mean atmospheric fields are equivalent barotropic in structure everywhere, with large, statistically significant changes in regions far from the surface temperature anomaly. The steady-state linear response does not at all resemble the nonlinear solution in such cases. In addition, for baroclinically unstable zonally asymmetric flows, the response is relatively insensitive to the longitudinal position of the surface temperature anomaly. The climatic implications of these model results are discussed.