Deep variability in the Atlantic Western Boundary Current based on altimetric and expendable bathythermograph data

The deep variability in two areas of the Atlantic Western Boundary is studied. One site is located at 38 degrees N, inshore of the Gulf Stream. The other is at 8 degrees S, off the Brazilian coast. Analyses are centered on current time series estimated by a method that uses expendable bathythermograph derived dynamic heights to remove the near-surface signal from altimetric sea surface height. Both series are approximately 6 years long. Currents are compared to scatterometer derived alongshore wind stress and basin-wide wind stress curl. In both areas, current variability is correlated to basin-averaged wind stress curl and also to alongshore wind stress. The relationship between currents and wind curl is coherent with the western boundary currents response to interior Sverdrup flow. We propose that alongshore wind stress exerts control over the flow by divergence of the Ekman flow at the coast. In the north, the variability is dominated by interannual oscillations of the wind curl. The effects of the alongshore stress are secondary and have annual frequency. In the southern site, the alongshore effect appears to be the dominant forcing. The main observed results are confirmed by data from a numerical model with 1/6 degrees horizontal resolution.