UC Santa Barbara

The South Atlantic Convergence Zone (SACZ) isan intrinsic characteristic of the South American SummerMonsoon. In a recent study, we verified that the main modeof coupled variability over the South Atlantic (South AtlanticDipole (SAD)) plays a role in modulating the position ofextratropical cyclones that affect the SACZ precipitation. Inthis study, we perform numerical experiments to further investigatethe mechanisms between SAD and the SACZ. Numericalexperiments forced with prescribed SST anomaliesshowed that, even though the Atlantic SSTaffects the positionof the cyclone associated with the SACZ, the atmosphericresponse and precipitation patterns over land are opposed tothe observations. On the other hand, experiments forced withprescribed anomalous driving fields showed that the atmosphericcomponent of SAD plays a significant role for theright position and intensity of precipitation associated with theSACZ. SAD negative anomalies provide the low-level andupper-level atmospheric support for the intensification of thecyclone at surface and for the increase in precipitation over theland portion of the SACZ. Therefore, the numerical experimentssuggest that, during El Niño Southern Oscillation neutralconditions, the SACZ precipitation variability associatedwith SAD is largely dependent on the atmospheric variabilityrather than the underlying SST.