The Structure of the Inter-Tropical Convergence Zone in Equatorial Africa and Its Relationship to East African Rainfall

Mean monthly airflow charts for five levels over equatorial Africa, constructed from radiosonde and pilot balloon data, allow the movement of the I.T.C.Z. over equatorial Africa to be traced from month to month. Three monsoons, their principal flow lines controlled by topography, and three upper-air masses interact within the I.T.C.Z. and the seasonal limits of the air masses at lower levels relate to the East African rainfall pattern. Pulses of low-level westerly air originating over the Atlantic coincide with rainfall in western Tanzania in February and March and with rainfall in Uganda from June to September. The structures in the I.T.C.Z. appear to be similar to the West African and Indian models. The divergence field shows the influence of the monsoon seasons and suggests structural differences between East Africa's two main rainy seasons. East Africa lies in a zone of interaction between the West African and Indian monsoon systems and its weather and climate form a distinctive pattern in this context.