Extended Abstract (156K)9B.1
Rainfall variability and convection in african easterly wave regime
Arona Diedhiou, IRD/LTHE, Grenoble, France; and H. Laurent, T. Lebel, and C. Lauaysse
Using NCEP/NCAR reanalyses, NOAA OLR and observed IRD rainfall over West Africa from 1979 to 1990, we have investigated the variability of rainfall and convection over Niamey (Niger, West Africa) during African Easterly waves activity. After detecting on each year the dates of 3-5-day wave activity and considering thresholds on the associated observed rainfall and convection, we have identified two classes of convective events. The first one defines the so-called wet convective events that are associated with cold top clouds and strong rain amount at the surface. The second class is the class of dry convective events associated to cold top clouds and weak observed rain amount at the surface. For each class, the easterly wave characteristics have been analyzed as well as the associated instabilities and energy conversions. A composite analysis shows that in wet event regime, convection is deeper and located in and ahead of the wave trough. The associated monsoon flow has the deepest thickness and the largest meridional extension; the African easterly jet (AEJ) core is weaker in magnitude than average and is located further to the north. These wet events represent only 20% of the total events and explain about 40% of the total rainfall in easterly wave regime. In dry event regime, convection is in general shallower than in wet event regime and is located in and behind of the trough. These events are more frequent and the associated AEJ core is larger in magnitude than average. The study shows the necessity to well define the interactions between wave, rainfall and convection at seasonal scale to understand the interannual variability of rainfall over West Africa.
Session 9B, Large-Scale Dynamics and Convection IV (Parallel with Sessions 9A, 9C, and 9D)
Wednesday, 1 May 2002, 11:00 AM-12:30 PM
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