Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 2 2009 10.5194/os-5-141-2009 http://www.ocean-sci.net/5/141/2009/ http://www.ocean-sci.net/5/141/2009/os-5-141-2009.html http://www.ocean-sci.net/5/141/2009/os-5-141-2009.pdf 141 153 2009-05-18 Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves C. Guiavarc'h A. M. Treguier treguier@ifremer.fr A. Vangriesheim Laboratoire de Physique des Oceans, IUEM, CNRS-IFREMER-IRD-UBO, BP 70, 29280 Plouzané, France Laboratoire Environnement Profond, IFREMER, BP 70, 29280 Plouzané, France Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, UK In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5° S show very energetic biweekly oscillations at 1300 m depth. A high resolution primitive equation numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastally-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast of the Gulf of Guinea, especially in the 10–20 day period range and at depths between 500 and 1500 m. The kinetic energy distribution is well explained at first order by linear theory. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is influenced by the details of the bathymetry. Along the coast, baroclinic modes 3 to 5 are important close to the equator, and the signal is dominated by lower vertical modes farther south. 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