South Atlantic Circulation and Variability from a Data Assimilating Model

Abstract

We characterize the low frequency variability of the South Atlantic circulation using 50 years of data from the SODA model. EOF analysis show that the leading modes of sea surface height anomalies (SSH) are dominated by interdecadal variations of the subtropical gyre. The dynamical manifestations of the Brazil-Malvinas Confluence and the Agulhas Retroflection variability appear in the second and third mode. The structure of the wind stress curl show changes related mostly to the first SSH mode. The lack of significant correlation between the SSH and wind curl for the second and third modes indicates that these patterns are more influenced by the internal variability of the geostrophic flow. There are significant correlations between SSH and surface temperature anomalies (SST), suggesting that an important portion of the SST variability are driven by advective effects associated with the geostrophic circulation. Our analysis also shows a strong correlation between the SA meridional overturning circulation (SAMOC) and the meridional heattransport (MHT), with a latitudinal increase that is close to obervations. The anomalies and the meridional gradient of the SAMOC and MHT appear stronger during El Niño years and weaker during La Niña ones.