The annual cycle of The Brazil—Malvinas Confluence region in the NCAR Climate System Model

The mean and seasonal variability of the circulation in the Southwest Atlantic are investigated with a 300-yr integration of the National Center for Atmospheric Research's Climate System Model(CSM). The area of study is confluence region between the subtropical and subpolar waters represented by the Brazil and Malvinas currents. The seasonal variation of transport, its relationship to changes in the wind-stress forcing and in the sea surface temperature is examined and compared to available oceanographic observations. Results from this work show that the CSM transport values are very close to observed values. At approximately 38S they are consistent with hydrographically derived values obtained for the region. Furthermore, the seasonal cycle and magnitude of CSM transports across 30W between 10S-20S are similar to those obtained from TOPEX altimetry data. Our results also show that the separation of the Brazil and Malvinas currents from coast in the model has a range of 20-12 degrees latitude, respectively, which is very similar to the range observed in the Reynolds and Smith, 1994 climatology . The CSM seasonal cycle in transport associated with both the Brazil and Malvinas currents and its meridional displacement is closely linked to the seasonal variations in the wind stress curl. The transport of the CSM-derived Brazil current is higher during austral winter and smaller during austral summer. Conversely, the Malvinas current transport is weaker during austral winter and stronger during austral summer. The CSM shows that the seasonal oscillation of the confluence is related directly to transport variations of the constituent currents.