Dynamics of the equatorial Atlantic from altimetry

The first 700 days of TOPEX/POSEIDON altimetric data of the equatorial Atlantic are selectively investigated to yield a basin-wide description of the zonal pressure gradient along the equator and the meridional gradient across the North Equatorial Countercurrent (NECC). In the first analysis the gravest empirical orthogonal function mode is found to be zonally constant in midbasin and a quasi-stationary linear relationship between the basin-wide, averaged zonal wind stress and the zonal pressure gradient is demonstrated (correlation coefficient of 0.70 with a zero lag). In the second analysis the zonal variation of the depth of the NECC trough across the basin is described and it and its annual cycle are reproduced with a reduced-gravity model calculation (correlation coefficient of 0.75). A secondary result of both analyses is an estimate of the adjustment to the working model of the local geoid gradients needed to bring the mean altimetric signal into agreement with the dynamic models and modeled wind field.