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Abstract:
The upper-ocean circulation of the tropical Atlantic is a complex superposition of thermohaline and wind-driven flows. The zonally and vertically integrated upper-ocean meridional flow is associated with the upper branch of the Atlantic Meridional Overturning Circulation (AMOC) — a major component of the global climate system. In the tropics, the northward AMOC flow is superimposed by the shallower overturning associated with the wind-driven Subtropical cells (STC). At the western boundary, the TRACOS (TRopical Atlantic Circulation & Overturning at 11°S) array consists of tall moorings monitoring the strong western boundary current (WBC) system - more specifically, the North Brazil Undercurrent (NBUC) and the Deep Western Boundary Current (DWBC) as part of the AMOC and STC. Mean transports seem rather stable throughout the observations (between 2000-2004 and 2013 up to date), while long-term changes in water mass properties are detected and related to changes in remote areas. At the eastern side the Angola current is observed since 2013 and shows weak mean circulation, whereas the variability seems dominated by remotely forced waves from the equatorial region. In addition to the boundary observations, the program at 11°S was extended to observe the basin wide circulation with bottom pressures sensors on both sides of the basin. The available data is used to estimate AMOC variability at 11°S on seasonal to interannual time scales. Together with other AMOC arrays, this array has great potential for understanding mechanisms relevant for tropical Atlantic variability, as well as meridional coherence and long-term changes of AMOC variability.
