West African palaeosynoptic patterns at the last glacial maximum

Summary The composite method and an atmospheric moisture budget is applied to study the present synoptic summer situation in the West African Sahel. This allows the information of the synoptic scale flow systems at the last glacial maximum to be obtained. Relying on the results of general circulation models and of local geological findings the palaeosynoptic situation was found to consist of the same constituents as today's given pattern. In both time slices the strength of the midtropospheric African Easterly Jet determines the intensity and frequency of the Sahelian synoptic disturbances: the Easterly Waves and the Squall Lines. The glacial rainfall intensity of the Squall Lines, the most effective rain-bearing system of the Sahel, is calculated to be 2/3 of the modern one. Additionally, only half the number of Squall Lines propagated across the West African continent per summer month. Thus the glacial rainfall amount of the Sahel was roughly 30% of the value observed today.With 6 Figures