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Communication incl. Poster: BibTeX citation key:  Giordani
Giordani, H., Caniaux, G. & Wade, M. 2009. On the formation of the Atlantic Cold Tongue in the Gulf of Guinea during the AMMA/EGEE-3 Experiment. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Added by: roussot 2009-10-22 20:59:31
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Categories: Ocean processes, Ocean-atmosphere interactions
Creators: Caniaux, Giordani, Wade
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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Abstract
Vertical velocity (w) plays a central role during the development of the Atlantic Cold Tongue (ACT) from May to July in the Gulf of Guinea. This paper aims at identifying the sources of vertical velocity and their interactions in the ACT set up during the AMMA-EGEE experiment in 2006. Sources of w are derived from the divergence and vorticity equations in the primitive equation frame and diagnosed online in a regional ocean model of the Atlantic equatorial basin.
Results show that the vertically and horizontally sheared system formed by the surface and subsurface currents is the most important source of vertical motion. This source of vertical velocity is permanently balanced by the pressure field. Wind intensification events, associated with the intraseasonnal variability of the Santa Helena anticyclone, modify the equatorial circulation, which finally force the pressure field to readjust to the new dynamic conditions. This readjustment mechanism is the source of a net upward motion in the ATC, close to the equator; it produces intermittent sea surface temperature cooling in boreal spring and summer.
The important result of this contribution is that winds are not the direct source of vertical motion in the ocean, like in the Ekman pumping theory (well suited for an ocean initially at rest), often used in the literature to interpret the formation of the ACT. Winds should be rather seen as an indirect source of permanent imbalance between the dynamics and mass fields, which is at the origin of the vertical velocity in the ACT.
Added by: roussot