2002 Annual

Monday, 14 January 2002
Challenging and Modifying the Historical view of the West African Monsoon using TRMM Satellite Data
Segayle C. Walford, Penn State Univ., University Park, PA; and G. Jenkins
The historical view of the West African Monsoon was established in the colonial time frame (1900-1960). It was developed on a regional basis through the rain gauge network. This view depicted four weather zones associated with the West African Monsoon. The significant rain was located in zone C, which was broken up into a northern and southern zone. The northern zone was predominately composed of convective rain, giving way to lighter stratiform rain in the southern zone. The other zones (A, B, and D) produced only small amounts of rain. Zone C is generally located several hundred km south of the intertropical front (ITF) where northeast and southwest winds converge. From the historical viewpoint, there is a direct relationship between the ITF and zone C. The ITF and zone C both move north from May through August, and retreats equatorward in September and October. This historical view is reevaluated and modified using TRMM satellite data. In particular TRMM precipitation radar (TRMM pr) and TRMM merged rain estimates from 1998 to 2000 (June - September). We will examine the movement of the monsoon at 0 degrees and relate its movement to the African Easterly Jet (AEJ), which we believe is the primary controlling mechanism for rain in West Africa.

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