Propagating Modes of Variability and Their Impact on the Western Boundary Current in the South Atlantic

Studies have suggested that the South Atlantic Ocean plays an important role in modulating climate at global and regional scales and thus could serve as a potential predictor of extreme rainfall and temperature events globally. To understand how propagating modes of variability influence the circulation of the subtropical gyre and the southward flowing Brazil Current (BC) at interannual frequencies, a Complex Empirical Orthogonal Function (CEOF) analysis was performed on the satellite-derived sea surface height (SSH). The first three CEOF modes explain about 23%, 16%, and 11% of the total interannual variability and show clear westward propagation with phase speeds comparable to that of theoretical baroclinic mode 1 Rossby waves. Results suggest that there is a change in the way energy is distributed among the modes before and after 2005. Before 2005, the SSH variability in the western boundary in the South Atlantic and the volume transport of the BC are more closely linked to the first and the second modes, while the third mode dominates after 2005. This change in energy distribution around 2005 is associated with the recent El Nino-Southern Oscillation (ENSO) regime shift in the Pacific Ocean via atmospheric teleconnections. We found that the first CEOF mode is strongly correlated with eastern Pacific (i.e., canonical) ENSO events and the Pacific Decadal Oscillation, whereas the third CEOF is correlated to central Pacific (i.e., Modoki) ENSO. These results are useful to understand the overall dynamics of the South Atlantic and to potentially improve predictability of Meridional Overturning Circulation and monsoon pattern changes around the world. Plain Language Summary The South Atlantic Ocean plays a major role in modulating climate at global and regional scales and therefore can serve as an important predictor of extreme weather events globally. Here we focus on understanding the large-scale propagating modes of sea surface height (SSH) in the South Atlantic Ocean and explore their importance to the interannual variability of the Brazil Current. The propagating modes are estimated by performing a Complex Empirical Orthogonal Function (CEOF) analysis of the satellite-derived SSH at interannual frequencies. The CEOF modes exhibit Rossby wave-like propagation, and they greatly influence the SSH near the western boundary. Results show that the equatorial Pacific Ocean modulates the interannual variability of the CEOF modes via atmospheric teleconnections and thereby influences the southward flowing Brazil current. The results of this study are useful to understand the overall dynamics of the South Atlantic and to potentially improve predictability of Meridional Overturning Circulation and monsoon pattern changes globally.