JUNE-SEPTEMBER RAINFALL IN NORTH-EASTERN AFRICA AND ATMOSPHERIC SIGNALS OVER THE TROPICS - A ZONAL PERSPECTIVE

The connection between rainfall in northeast Africa (Djibouti, Eritrea, Ethiopia, Kenya, Somalia, Sudan, and Uganda) and various atmospheric indicators from the tropics have been investigated for the northern summer season. Variables used include zonal wind at 700 hPa and 200 hPa, sea-level pressure, and rainfall over other tropical areas, for the period 1951-1988. Strong significant correlations are shown with the Southern Oscillation and the components of the Walker cell in the Pacific Ocean. Draughts in the Ethiopia-Uganda area are associated with El Nino events and moreover, with above normal pressure and droughts over India. Other significant relationships exist with the African monsoon. Westerly (easterly) anomalies in the lower (upper) levels are associated with abundant summer rainfall years in north-east Africa. These results are all consistent with the previously defined Walker-type circulations over the tropics, particularly as far as the Indo-Pacific and African cells are concerned. Although the Southern Oscillation has a dominant impact in this respect, the specific coherence of the African cell is further evidenced Preliminary findings suggest that the summer rainfall areas of East Africa could qualify as a location for the rising branch of this cell.