On the Baroclinic Response of the Zonal Pressure Gradient in the Equatorial Atlantic Ocean

Temperature time series obtained from surface moorings deployed along the equator in the Atlantic Ocean during the Seasonal Response of the Equatorial Atlantic Experiment and the Programme Français Océan et Climat dans l\u27Atlantique Equatorial were used to investigate the baroclinic response of the zonal pressure gradient due to the sloping isopycnals. The zonal pressure gradient evolved as a complicated function of time, depth, and zonal position. The most rapid and spatially inhomogeneous variations corresponded to periods of rapidly changing easterly wind stress. Following these periods the baroclinic response due to the sloping isopycnals was observed to overshoot its intended equilibrium before relaxing to it. In so doing, it tended to buffer pressure gradient variations at the depth of the Equatorial Undercurrent (EUC). Over much of the year the isopycnal slopes opposed the surface slope. After the winds relaxed in winter, however, the isopycnal slopes reversed and acted in concert with the surface slope, thereby enhancing the pressure gradient at the depth of the EUC relative to that at the surface. This reversal might be important in maintaining the EUC during times of weak easterly wind stress. The vertical structure of the zonal pressure gradient varied with the depth of the thermocline. When the winds were weak and the thermocline was shallow, the baroclinic response of the zonal pressure gradient due to the sloping isopycnals was primarily effected in the upper 50 m. After the winds intensified and the thermocline deepened the baroclinic response extended down to at least 150 m