Teleconnections modulating inter-annual climate variability over northern Namibia

Abstract

Regional teleconnections that anticipate and sustain anomalous climatic conditions in northern Namibia are studied. A rainfall index is formulated using 11 stations in the area 17-20°S, 15-19°E. The three wettest and three driest summers are selected: 1974, 1976, 1978 and 1981, 1983, 1988 to produce composite maps of environmental fields at lags - 6 months, - 3 months and zero. Sea surface temperatures are warmer in dry years across most of the Atlantic and western Indian Ocean at all lags. Convection is more active in the central Indian Ocean during the OND season preceding a drought, according to satellite OLR. Upper westerlies are strong over the tropical Atlantic in the JAS season preceding a dry year, and a low level anticyclonic vortex is present in the South Atlantic. Together these indicate a Walker cell anomaly over the tropical Atlantic with lower easterly/upper westerly flow contributing to descending motion over Namibia and adjacent parts of southern Africa. The results help identify mechanisms underlying inter-annual climate variability over northern Namibia. From the analysis, a multiple linear regression model is formulated to predict the late summer rainfall. Its predictors and potential skill are outlined.