| Summary: | The relative importance of annular and nonannular characteristics in the wintertime Southern Hemisphere circulation is investigated using reanalysis data between 1978 and 2010. Weekly averaged data are chosen to capture the typically short time scale of intraseasonal atmospheric variability. In existing studies, the southern annular mode (SAM) has been shown to exhibit significant nonannular behavior in the western Southern Hemisphere during austral winter. Variability in this region is also characterized by wave-like disturbances, and this “overlap” in nonannular behavior between different climate modes has led to a lack of consensus when defining and measuring impact from these wave-like disturbances. A number of approaches are adopted, including empirical orthogonal function analysis, teleconnection correlation analysis, and the application of a vector autoregression model to isolate directions of causality and wave propagation. Austral winter variability is shown to be dominated by nonannular wave-like disturbances, rather than a seesaw pattern between high and middle latitudes. The wave-like disturbances have the largest amplitude in the western Southern Hemisphere, are quasi-stationary, and exhibit eastward propagation of information. This suggests that the dominant pattern of western Southern Hemisphere intraseasonal variability during austral winter, which is commonly associated with the SAM, is, in fact, a wave-like mode of variability.
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