Interdecadal Variability of Southeastern South America Rainfall and Moisture Sources during the Austral Summertime

Sea surface temperature (SST) anomalies over the tropical oceans generate extratopical atmospheric circulation anomalies that can induce rainfall variability and changes in the sources of moisture. This work evaluates the interdecadal changes in the moisture sources for Southeastern South America (SESA) during austral summer and it is divided into two complementary parts. In the first part we construct a climate network to detect synchronization periods among the tropical oceans and the precipitation over SESA. Afterwards, taking into account these results, we select two periods with different degree of synchronization to compare the spatial distribution of the SESA moisture sources.
Results show that during the last century there were three synchronization periods among the tropical oceans and the precipitation over SESA (during the '30s, '70s and '90s decades), and suggest that the main moisture sources of SESA are the recycling over the region, the central-eastern shore of Brazil together with its surrounding Atlantic Ocean, and the southwestern south Atlantic surrounding the SESA domain. Comparison of SESA moisture sources for the '80s (a period of non-significant synchronization) and the '90s (a synchronized period) shows that the principal differences are in the intensity of the recycling and in the strength of the central-eastern shore of Brazil. Moreover, we find that a region centered at (20ºS, 300ºE) is a moisture source for SESA only during the '90s. These differences can be associated with the development of a low-level anti-cyclonic (cyclonic) anomaly circulation over centraleast Brazil which favors the transport of moisture from central Brazil (central-east shore of Brazil) toward SESA in the '90s ('80s).