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Journal Article: BibTeX citation key:  Joly
Joly, M. & Voldoire, A. Role of the Gulf of Guinea and the Mediterranean in the interannual variability of the West African monsoon. IN Climate Dynamics, .
Added by: Mathieu Joly 2009-01-23 14:17:26
 B  
Categories: Ocean-atmosphere interactions
Keywords: Climate
Creators: Joly, Voldoire
Collection: Climate Dynamics
Bibliographies: cnrm, Prior150410

Peer reviewed
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Popularity index:  55.02%
Maturity index:  submitted

 
Abstract
The oceans explain a significant part of the interannual variability of the West African monsoon (WAM). This paper explores the role of the Gulf of Guinea and of the Mediterranean. What are the physical processes of those ocean-atmosphere interactions in the atmospheric reanalyses? How are they simulated by CMIP3 climate models?
The "Atlantic Niño" is the main mode of interannual variability in the Gulf of Guinea. SST anomalies are maximum in June-July, and are associated with a convective anomaly in the marine ITCZ, that spreads over the Guinean coast. In the atmospheric reanalyses, the strong anomalies in the low layers (temperature, humidity, and wind) appear to be the main contributors to the modulation of WAM seasonal rainfall. The absence of any evident shift in the position of the monsoon rainbelt (the so-called "rainfall dipole") is justified by the collapse of the correlations between Gulf of Guinea SST and Sahel rainfall at the end of the 20th Century. It is suggested that this may be due to the counteracting effects of the Pacific and Atlantic basins over the last decades. In most of the studied CMIP3 simulations, the interannual variability of SST is too weak in the Gulf of Guinea, especially along the Guinean Coast. In five simulations, the simulated Atlantic Niño is correlated with decaying ENSO events. Finally, the influence on monsoon rainfall over the Guinean coast is hardly reproduced.
In the observation record, there is a weak - but statistically significant - relationship between Mediterranean SST and monsoon rainfall over the central Sahel. This SST-rainfall relationship is however not statistically significant in ERA40 and NCEP reanalyses. Nevertheless, the observed rainfall mode is strongly correlated with summer atmospheric anomalies over Europe, which suggests that Mediterranean SST may not play the major role in this tropical-extratropical relationship. Only two of the considered CMIP3 simulations have a significant and realistic Mediterranean-WAM relationship.
Added by: Mathieu Joly