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Published Online October 9, 2003
Science DOI: 10.1126/science.1089357

Reports

Submitted on July 18, 2003
Accepted on September 26, 2003

Oceanic Forcing of Sahel Rainfall on Interannual to Interdecadal Time Scales

A. Giannini 1*, R. Saravanan 2, P. Chang 3

1 National Center for Atmospheric Research, Boulder, CO 80305, USA; Present Address: International Research Institute for Climate Prediction, Palisades, NY 10964, USA
2 National Center for Atmospheric Research, Boulder, CO 80305, USA.
3 Department of Oceanography, Texas A&M University, College Station, TX 77843, USA.

* To whom correspondence should be addressed. E-mail: alesall{at}iri.columbia.edu.

Pervasive evidence is presented, based on an ensemble of integrations with NSIPP1 (version 1 of the atmospheric general circulation model developed at NASA's Goddard Space Flight Center in the framework of the Seasonal to Interannual Prediction Project) forced only by the observed record of sea surface temperature (SST) over 1930-2000, to conclude that variability of rainfall in the Sahel results from the response of the African summer monsoon to oceanic forcing, amplified by land-atmosphere interaction. The recent drying trend in the semi-arid Sahel is attributed to warmer-than-average low latitude waters around Africa, which, by favoring the establishment of deep convection over the ocean, weaken the continental convergence associated with the monsoon, and engender widespread drought from Senegal to Ethiopia.


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