INTERANNUAL VARIABILITY OF RAINFALL IN THE EASTERN HORN OF AFRICA ANDINDICATORS OF ATMOSPHERIC CIRCULATION

Relationships between rainfall variations in the Eastern Horn of Afric a, the Southern Oscillation, and the Indian Ocean temperature and pres sure surface fields are studied for the period 1932-83. Rainfall data consist of stations and regional indices calculated for three selected areas experiencing quite different rainfall patterns. The results ind icate significant negative correlations between northern autumn rains in Somalia and the Southern Oscillation during the same season. These rains are also negatively correlated with pressure in the Western Indi an Ocean, and positively correlated in the Eastern Indian Ocean. The r everse pattern is shown with sea-surface temperature. This agrees very well with the observations made in Kenya as far as the short rains of October-November are concerned. Central Ethiopia summer rains, in con trast, indicate significant positive correlations with the Southern Os cillation, at zero and 3 months lag. El Nino years often correspond to drought years in this region. Evidence of an inverse relationship bet ween the amount of rainfall in Ethiopia during summer (especially duri ng September) and both the pressure and sea temperature over the India n Ocean is also given. Correlations with the Arabian Sea are particula rly strong.However, teleconnections between summer rains in Northern E thiopia (Eritrea) and the ENSO or the Indian Ocean fields are much wea ker. These results suggest that, although summer rains over Ethiopia a re said to be related to the monsoon air flow from the Congo Basin and the Atlantic Ocean, there also exist quite strong connections with th e surface conditions prevailing in the Indian and Pacific Oceans.