Interannual Variability in Rainfall, Water Vapor Flux, and Vertical Motion over West Africa

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Abstract
This study examines large-scale forcing mechanisms as they relate to initiation and maintenance of recent, long-term drought conditions in sub-Saharan Africa. The analysis uses 31-yr datasets of rainfall, moisture flux, and vertical motion. Empirical orthogonal functions (EOFs) of the 500-mb vertical wind velocity indicate major modes of variability in large-scale general circulation features (e.g., Hadley–Walker circulation). The data record includes both pluvial and drought periods, and enables distinctions between the early and late rainy season, and between northern and southern sub-Saharan regions. Results suggest that changes in the general circulation were important in initiating drought in the Sahel, but other mechanisms may be responsible for the persistence of drought conditions. EOFs of vertical wind velocity indicate a marked change in the general circulation prior to drought onset in the 1960s. Similar changes in the general circulation in the 1970s did not accompany a return to wet ... Abstract This study examines large-scale forcing mechanisms as they relate to initiation and maintenance of recent, long-term drought conditions in sub-Saharan Africa. The analysis uses 31-yr datasets of rainfall, moisture flux, and vertical motion. Empirical orthogonal functions (EOFs) of the 500-mb vertical wind velocity indicate major modes of variability in large-scale general circulation features (e.g., Hadley–Walker circulation). The data record includes both pluvial and drought periods, and enables distinctions between the early and late rainy season, and between northern and southern sub-Saharan regions. Results suggest that changes in the general circulation were important in initiating drought in the Sahel, but other mechanisms may be responsible for the persistence of drought conditions. EOFs of vertical wind velocity indicate a marked change in the general circulation prior to drought onset in the 1960s. Similar changes in the general circulation in the 1970s did not accompany a return to wet ...

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