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Communication incl. Poster: BibTeX citation key:  Caniauxa
Caniaux, G., Giordani, H., Redelsperger, J.-L., Wade, M. & Guichard, F. 2009. The Santa Helena anticyclone, the Atlantic cold tongue and the African monsoon. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Last Edited by: Deleted user 2009-09-04 14:20:57
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Categories: Monsoon system and its variability, Ocean processes, Ocean-atmosphere interactions
Keywords: Atmospheric Boundary Layer
Creators: Caniaux, Giordani, Guichard, Redelsperger, Wade
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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Abstract
The Atlantic Cold Tongue (ACT) is the major seasonal signal which affects the eastern equatorial Atlantic basin. During its emplacement, sea surface temperatures (SST) decrease significantly south of the Equator. Cooling starts close to 10°W or some years along the western African coast and spreads quickly throughout the central and southern Gulf of Guinea (GG) between May and August. At the time of its maximum extent, this cooling occupies an oceanic surface equivalent to roughly a quarter that of the Sahara.
Correlations between the set up of the ACT and the African Monsoon onset date computed over the last 27 years, suggest that the set up of this extended oceanic cooling plays a key role on the African Monsoon onset. By using simple models, we will discuss the physical processes implied in the ACT setup, in the disturbances that it induces on the marine atmospheric boundary layer and in its potential role on the onset of the African Monsoon.
We suggest that the air-sea coupling occurs in two distinct phases: during the first phase (April-May), the ACT results from the intensification of the southeasterly trade winds associated to the seasonal northward displacement of the Santa Helena Anticyclone. During the second phase (June-July), winds increase / decrease north /south (respect.) of the Equator, as a result of significant SST gradients generated by the differential cooling between the ACT and tropical surface waters that circulate throughout the northern part of the GG. Atmospheric divergence and convergence are resulting at low levels north and south of the Equator respectively. Il contributes to the northward migration of humidity and convection over land. Consequently, the ACT contributes actively in the development of the African Monsoon during this second phase.
Last Edited by: Deleted user