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Journal Article: BibTeX citation key:  Fink2006a
Fink, A. H., Vincent, D. G. & Ermert, V. (2006) Rainfall Types in the West African Soudanian Zone during the Summer Monsoon 2002. IN Monthly Weather Review, 134. 2143–2164.
Added by: Andreas Fink 2010-08-19 14:01:50    Last Edited by: Fanny Lefebvre 2010-11-29 16:39:26
 B  
Categories: Atmospheric processes
Keywords: Dynamics, Rainfall, Soudanian zone
Creators: Ermert, Fink, Vincent
Collection: Monthly Weather Review

Peer reviewed
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Abstract
Enhanced surface and upper-air observations from the field campaign of the Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa (IMPETUS) project are used to partition rainfall amounts over the West African Sudanian zone during the 2002 summer monsoon season into several characteristic types and subtypes of precipitating systems. The most prominent rainfall subtype was fast-moving, long-lived, and extensive cloud clusters that often developed far upstream over the central Nigerian highlands in the afternoon hours and arrived at the Upper Ouémé Valley (UOV) after midnight. These organized convective systems (advective OCSs, subtype Ia) accounted for 50% of the total rain amount in the UOV catchment in Benin. Subtypes Ia and IIa (i.e., locally developing OCSs) were found to pass by or organize when a highly sheared environment with deep and dry midtropospheric layers was present over the UOV. These systems were most frequent outside the peak of the monsoon season. The second major type of organized convection, termed mesoscale convective systems (subtypes Ib, IIb, and IIIb) in the present study, contributed 26% to the annual UOV precipitation. They occurred in a lesssheared and moister tropospheric environment mainly around the height of the rainy season. A third distinct class of rainfall events occurred during an unusual synoptic situation in which a cyclonic vortex to the north of the UOV led to deep westerly flow. During these periods, the African easterly jet was lacking. The so-called vortex-type rainfalls (subtypes IIIa, IIIb, and IIIc) contributed about 9% to the annual rainfall totals.
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Added by: Andreas Fink    Last Edited by: Fanny Lefebvre