Nonstationary Impacts of the Southern Annular Mode on Southern Hemisphere Climate

SILVESTRI, GABRIEL; VERA, CAROLINA

JOURNAL OF CLIMATE

AMER METEOROLOGICAL SOC

Lugar: Boston, Estados Unidos; Año: 2009 vol. 22 p. 6142 - 6148

0894-8755

The temporal stability of the southern annular mode (SAM) impacts on Southern Hemisphere climateduring austral spring is analyzed. Results show changes in the typical hemispheric circulation pattern associatedwith SAM, particularly over South America and Australia, between the 1960s–70s and 1980s–90s. Inthe first decades, the SAM positive phase is associated with an anomalous anticyclonic circulation developedin the southwestern subtropical Atlantic that enhances moisture advection and promotes precipitation increaseover southeastern South America (SESA). On the other hand, during the last decades the anticyclonicanomaly induced by the SAM’s positive phase covers most of southern South America and the adjacentAtlantic, producing weakened moisture convergence and decreased precipitation over SESA as well aspositive temperature anomaly advection over southern South America.Some stations in the Australia–New Zealand sector and Africa exhibit significant correlations between theSAM and precipitation anomalies in both or one of the subperiods, but they do not characterize a consistentarea in which the SAM signal can be certainly determined. Significant changes of SAM influence on temperatureanomalies on multidecadal time scales are observed elsewhere. Particularly over the Australia–NewZealand sector, significant positive correlations during the first decades become insignificant or even negativein the later period, whereas changes of opposite sign occur in the Antarctic Peninsula between both subperiods.