Variability of the Atlantic off-equatorial eastward currents during 1993-2010 using a synthetic method

We have developed, validated, and applied a synthetic method to monitor the off-equatorial eastward currents in the central tropical Atlantic. This method combines high-density expendable bathythermograph (XBT) temperature data along the AX08 transect with altimetric sea level anomalies (SLAs) to estimate dynamic height fields from which the mean properties of the North Equatorial Countercurrent (NECC), the North Equatorial Undercurrent (NEUC) and the South Equatorial Undercurrent (SEUC), and their variability can be estimated on seasonal to interannual timescales. On seasonal to interannual timescales, the synthetic method is well suited for reconstructions of the NECC variability, reproduces the variability of the NEUC with considerable skill, and less efficiently describes variations of the SEUC, which is located in a region of low SLA variability. A positive correlation is found between interannual variations of the NECC transport and two indices based on an interhemispheric sea surface temperature (SST) gradient and southeasterly wind stress in the central tropical Atlantic. The NEUC is correlated on interannual timescales with SSTs and meridional wind stress in the Gulf of Guinea and zonal equatorial wind stress. This study shows that both altimetry and XBT data can be effectively combined for near-real-time inference of the dynamic and thermodynamic properties of the tropical Atlantic current system.