A new conceptual model for the meridional circulation of the West African monsoon

In situ sounding observations from selected sites in West and Central Africa are used to document the seasonal cycle in the lower troposphere associated with the seasonal migration in precipitation of the West African Monsoon. The main purpose of this exercise is to provide a description of the seasonal cycle free of errors and biases of numerical models, which can be substantial in this region. The most unique feature is a low-level (~700 hPa) northerly flow, which penetrate through the rainband in various phases of the seasonal cycle. The observations are synthesized into a schematic describing the salient features in the low-level circulation associated with the rainband in different phases of the seasonal cycle. This schematic circulation pattern in West Africa is in contrast to the traditional conceptual circulation pattern associated with the marine ITCZ and other monsoon systems.