The Seasonal Response of the Held-Suarez Climate Model to Prescribed Ocean Temperature Anomalies. Part II: Dynamical Analysis

Abstract

From an analysis of the heating associated with equatorial, subtropical and midlatitude ocean temperature anomalies in the Held-Suarez climate model, it is found that the magnitude of increase in vertical motion per unit heating in the vicinity of anomalies is relatively insensitive to latitude of the forcing, while the magnitudes of local 750-250 mb thickness changes per unit heating increase sharply as the ocean temperature anomaly is shifted poleward. For equatorial and subtropical anomalies the seasonal variation of the anomalous local vertical motion and thickness fields is in-phase with that of the anomalous local heating, but in the case of the midlatitude anomaly the seasonal changes of local thickness and heating are not synchronous. The steady-state linear shallow water equations on the equatorial and midlatitude beta planes provide a useful framework for explaining the dynamics of these phenomena. Linear theory is less successfully applied to the analysis of the remote cross-latitudinal response of the model atmosphere to ocean temperature anomalies. Several possible physical explanations for the apparent violations or the predictions of linear theory are explored, but are ultimately rejected as credible hypotheses. Instead, it is shown that the errors arising from limited sampling of the seasonal climatic states of the model are probably the principal ?cause? of the large-amplitude departures of 750?250 mb thickness in regions far-removed from the ocean temperature anomalies in certain seasons. The implications of these results for the prediction of seasonal climate are discussed.