Physical processes associated with summer precipitation increase over southeastern South America in a global warming scenario

Southeastern South America (SESA) is one of the few subtropical regions where WCRP/CMIP3 coupled general circulation models project significant summer rainfall increases by the end of the twenty first century, in a global warming scenario. This signal is revealed to be associated with a frequency increase of positive phase of the leading pattern of austral summer rainfall variability in the region. The positive phase manifests as austral summer rainfall above (below) normal in the SESA (South Atlantic convergence zone) region. Moreover, the rainfall pattern change is shown to be associated with positive anomalies of the sea surface temperature (SST) in the equatorial Pacific. This result is confirmed by numerical sensitivity experiments performed with the LMDZ4 " two-way nesting " interactive climate models system, which also showed that the projected rainfall increase in SESA is mainly associated to the zonally asymmetric pattern of the tropical SST warming.