The South American Monsoon System

Research on the Asian monsoon has provided enormous contributions to climate science and contributed to enhance awareness on the impacts of climate on society. A collateral contribution of Asian monsoon research has been the encouragement of studies on other monsoon systems of the world. This talk focuses on the second largest of such systems: the South American monsoon (SAM). SAM affects large parts of the continent over which it develops, their population, agriculture, and economies.

The presentation starts with SAM’s climatology and variability. The evolution during spring and summer of the region of intense convection over South America, establishment of the monsoon high over Bolivia, and development of the South Atlantic Convergence Zone (SACZ) are described. A strong low-level jet along the eastern slopes of the Andes is shown to be a key contributor to the moisture flux from the tropics to the mid-latitudes. As in all monsoons, oceanic effects on SAM are of great importance. The relationship between the strength of SACZ convection and low-level inflows from the southern Atlantic Ocean is discussed.

Next the presentation focuses on SAM’s variability. There is compelling evidence that ocean-atmosphere interactions involving the Pacific and Atlantic oceans play a major role in determining the variability of SAM in several time scales, particularly the interannual but also in the interdecal. In reference to the SACZ, its variability is linked to sea surface temperature anomalies in the tropical Pacific and North Atlantic, and in the southern subtropics of this ocean. Associations among extreme temperature months in the SAM region and concurrent extreme events of El Niño Southern Oscillation (ENSO), Atlantic Niño, Pacific Decadal Oscillation (PDO), and the Southern Annular Mode (SAM) are discussed. Finally, the possibility that the observed warming over northern South America has an anthropogenic origin is evaluated.