Inter-annual variability of short rains over northern Tanzania

The structure and variability of inter-annual circulation anomalies and precursors over northern Tanzania are investigated. Northern Tanzania experiences bimodal rains centered on: March to May ('long' rains) and October to December ('short' rains), our focus here. Areal rainfall departures in the period 1960 to 1990 are used to identify wet and dry years. Composite fields of sea surface temperature (SST), outgoing longwave radiation (OLR) and winds in the lower and upper troposphere are analysed at lags 0, –2, –4 and –6 mo. The historical mean is subtracted to produce anomalies. The patterns indicate an east-west gradient in SST anomalies across the Indian Ocean which corresponds with a zonal circulation and enhanced convection over the western basin, and increased rainfall over northern Tanzania. A multiple regression model is developed using 3 tropical predictors in the July to September period. The model accounts for about half of short-rain rainfall variance in the 1970s and 1980s.