HR: 09:36h
AN: A51F-08    [Abstracts]
TI: Modes of Variability in the West African Monsoon and their Relevance to Climate Change
AU: Vizy, E K
EM: ekv3@cornell.edu
AF: Cornell University, Dept. Earth and Atmos. Sci 3114 Snee Hall, Ithaca, NY 14853 United States
AU: Patricola, C M
EM: cmd58@cornell.edu
AF: Cornell University, Dept. Earth and Atmos. Sci 3114 Snee Hall, Ithaca, NY 14853 United States
AU: * Cook, K H
EM: khc6@cornell.edu
AF: Cornell University, Dept. Earth and Atmos. Sci 3114 Snee Hall, Ithaca, NY 14853 United States
AB: Two modes of regional climate variability on interannual time scales over West Africa are investigated, and their relevance for past and future climate is examined. One mode involves a low-level westerly jet, recently identified in high-resolution satellite observations and well simulated in a regional climate model (RCM). In today's climate, relatively wet conditions can be associated with an intensification of this jet, which is accompanied by increased moisture transport into Sahelian Africa from the Atlantic. RCM simulations of the African Humid Period, 6-8 ka, show that the westerly jet was also stronger during that time of enhanced summertime insolation. The "greening" of the Sahara and Sahel during that time was related to enhanced moisture advection and convergence by the westerly jet and not with, for example, enhanced southerly monsoon flow across the Guinean coast. Another prominent mode of interannual variability over West Africa is drying across Sahelian Africa during years of relatively warm sea surface temperatures in the Gulf of Guinea. When the Gulf of Guinea is 1-2 K warmer than the climatology, rainfall along the Guinean coast to the north is enhanced due to stronger evaporation over the Gulf. The resulting strong condensation heating induces northerly flow over the Sahel, which sinks to conserve potential vorticity. Convection is suppressed, and anomalously low precipitation rates are induced. This mode of variability has implications for future climate, and the relationship between greenhouse-gas induced warming of the Gulf of Guinea and the occurrence of Sahelian drought is explored.
DE: 3329 Mesoscale meteorology
DE: 3374 Tropical meteorology
DE: 1610 Atmosphere (0315, 0325)
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting