South Atlantic Multidecadal Variability in the Climate System Model

Strong multidecadal variability is detected in a 300-yr integration of the NCAR Climate System Model in the South Atlantic region, through the application of two signal recognition techniques: the multitaper method and singular spectrum analysis. Significant oscillations of a 25–30-yr period are found in the sea surface temperature, sea level pressure, and barotropic transport fields. A similar-scale signal is also captured in about one century-long observational records. A composite analysis of several model variables is performed based on the extremes of the sea surface temperature oscillation. The proposed mechanism for this basin-scale multidecadal signal involves changes in the intensity of the westerlies, associated with variability in the southward extension of the subtropical anticyclone, which drives changes in the ocean mass transport. This results in variability in the intensity of the Malvinas western boundary current and in the position of the Brazil–Malvinas confluence zone. Anomalous advection of cold waters northward (warm waters southward), owing to a strong (weak) Malvinas Current, is responsible for sea surface temperature anomalies in the subtropical western South Atlantic.