CONICET | Buscador de Institutos y Recursos Humanos

The temporal stability of the Southern Annular Mode (SAM) impacts on Southern Hemisphere climate during austral spring is analyzed. Results show changes in the typical hemispheric circulation pattern associated with SAM, particularly over South America and Australia, between 1960s-1970s and 1980s-1990s. In the first decades, SAM positive phase is associated to an anomalous anticyclonic circulation developed in the southwestern subtropical Atlantic that enhances moisture advection and promotes precipitation increase over southeastern South America (SESA). On the other hand, during the last decades the anticyclonic anomaly induced by SAM positive phase, covers most of southern South America and the adjacent Atlantic producing weakened moisture convergence and decreased precipitation over SESA as well as positive temperature anomaly advection over southern South America. Some stations in Australia-New Zealand sector and Africa exhibit significant correlations between SAM and precipitation anomalies in both or one of the sub-periods, but they do not characterize a consistent area in which SAM signal can be certainly determined. Significant changes of SAM influence on temperature anomalies on multi-decadal time scales are observed elsewhere. Particularly over Australia-New Zealand sector, significant positive correlations during the first decades become insignificant or even negative in the later period, while changes of opposite sign occur in the Antarctic Peninsula between both sub-periods.