Ocean impact on the South American summer precipitation

Improving our understanding of ocean-atmosphere feedbacks in the western South Atlantic region can improve our ability to predict extreme weather events, as well as the seasonal forecasting predictive skill in the region. Here, the summer precipitation in the South American Convergence Zone (SACZ) is investigated through observations and global coupled models (GCM). Satellite, in situ ocean observations and GCM with eddy-resolving ocean component show that the southern cell of the South Atlantic subtropical gyre is eddy rich, with strong sea surface temperature (SST) variability that may be modulated by gyre variability, Brazil Current variability or surface heat fluxes, and can have implications of atmospheric processes. During warm phases of the southern gyre, we find enhanced convective precipitation over the southern cell and reduced precipitation to the north that extends to coastal regions in eastern Brazil, a dipole-pattern similar to an active southern SACZ. Anomalous large-scale atmospheric circulation supports a convergence over the southern gyre, and coupled with the presence of warm SST, fuels convection in this region that coincides with the southern extension of the SACZ.