Extended Abstract (136K)P1.53
Impact of greenhouse warming on the variability of easterly waves, rainfall and convection over West Africa
Arona Diedhiou, LTHE/IRD, Grenoble, France; and J. F. Royer, I. Poccard, and T. Lebel
Using a 1950-2050 transient simulation of the impact of increasing amounts of greenhouse gases and aerosols on climate performed by the coupled atmosphere-ocean general circulation model of Meteo-France, we have analyzed the variability of the African easterly waves, rainfall and convection. In this simulation, the observed gas concentrations have been updated each year from 1950 to 1999 and then according the estimation of the new scenario of IPCC from 2000 to 2050. Anthropogenic sulfate aerosols and ozone photochemistry have been taken into account. A validation study has been done using NCEP/NCAR reanalyses by considering the 1950-1969 wet period over West Africa, the 1970-1990 dry period and the recent period (1991-2000). The coupled model reproduces the main features of the West African climate and simulates a realistic seasonal cycle of rainfall and monsoon variability. However, rainfall is overestimated both in magnitude and in latitudinal evolution, while the Tropical Easterly Jet and the African Easterly Jet are underestimated in magnitude. A tendency to an increase of the temperature at 850 hPa over the whole domain has been simulated with an increase of rainfall over Sahel, while over Guinea Coast, there is almost no change. Overall, in spite of the systematic biases, the characteristics of the african easterly waves and their modulation of rainfall and temperature are well simulated by the coupled model. Their kinematics properties (tracks, wavelength and velocity) are realistic except that there is no clear propagation over the eastern Atlantic. The tendancy to an increase of rainfall over Sahel is coherent with a northward migration of easterly waves activity area.
Poster Session 1, Tropical Cyclones, Large-scale Dynamics and Convection
Monday, 29 April 2002, 11:00 AM-12:30 PM
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