Variability of the Equatorial undercurrent in the eastern tropical Atlantic: Analysis of the 2007-2011 TACE-EUC Experiment

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The Equatorial Undercurrent (EUC) is a quasi-permanent feature of the zonal equatorial circulation in both the Atlantic and Pacific oceans. Its main role in both oceans is to supply thermocline waters from the shallow subduction zones in the subtropics to the main upwelling zones in the central and eastern part of the equatorial basins. While in the Pacific Ocean the EUC is rather well-described from nearly two decades of intensive shipboard and time-series observations in the tropical Ocean Atmosphere programs, the EUC in the Atlantic has until recently been relatively poorly sampled and neither its mean structure across the basin or its seasonal-to-interannual variability is understood. Its linkage to warm and cold phases of the boreal summer equatorial cold tongue is also poorly understood. During 2007-2011, a coordinated set of moored current meter observations has been collected across the central and eastern equatorial Atlantic during 2007-2011 by German, French, and U.S. investigators. These observations contribute to the goals of TACE (the Tropical Atlantic Climate Experiment), a 2007-2012 international CLIVAR program designed to improve climate predictions for the tropical Atlantic region, with a particular focus on the eastern equatorial Atlantic. The U.S. part of this effort consisted of moored ADCP current profile measurements at four sites along 10W and 0E, complementing a French (PIRATA) ADCP mooring at 10W, and an array of moorings along 23W maintained by IFM-GEOMAR (Germany). This project will complete the analysis of the data collected in this program, following the original NSF grant that supported the U.S. measurements. Intellectual Merit:The variability of the EUC across the basin, its linkages to wind forcing and SST variability, and the nature of the intraseasonal variability along the equator will be documented. The data will be used together with models to understand the dynamics controlling the EUC variability and the fate of EUC waters in the eastern Gulf of Guinea. The results of this analysis are expected to lead to a vastly improved understanding of the EUC in the Atlantic.Broader Impacts:The data collected from the TACE program, including all moored time series and cruise data, is being assembled into a web-accessible database maintained by the TACE Observations Working Group (http://tace.ifm-geomar.de/index.html), to provide ready access to the broader research community. The program has also provided graduate student training opportunities and promoted collaboration and sharing of technical expertise among international partners. The study will also contribute to an improved understanding of processes influencing SST variability in the eastern tropical Atlantic and associated climate variability in the tropical Atlantic region.