Teleconnection between Seasonal Rainfall over East Africa and Global Sea Surface Temperature Anomalies

Abstract

In this study, global sea surface temperature anomalies within ±30° latitudes of the equator were correlated with the time series of the major rotated principal component analysis (RPCA) modes of the seasonal rainfall over East Africa (Kenya, Uganda and Tanzania) for the period 1950-79. Regionally averaged rainfall anomalies were also correlated with the SST anomalies. The physical reality and climatological stability of the computed correlations were investigated using 6° by 6° gridmesh SST records instead of the original 2° by 2° values. The stability of the patterns were further tested by random removal of a maximum of upto five pairs of the SST and rainfall records from the original data sets. The results from the study indicate significant instantaneous (zero lag) and time lagged correlations between SST anomalies over portions of the global oceans and some of the principal seasonal rainfall modes in East Africa. The maximum instantaneous correlations occur in the boreal autumn between SST anomalies in the Pacific Ocean and the autumn rainfall RPCA mode, which is dominant over the coastal regions. The spatial patterns of the significant correlations indicate a 'see-saw' pattern between the eastern Pacific Ocean and the Indonesia region which coincides with positive rainfall anomalies over the coastal regions of East Africa, and indicates a relationship between rainfall variability in this region and the El Nino/Southern Oscillation (ENSO) phenomena. Lower spatial and temporal persistence is observed between SST anomalies and the rainfall RPCA modes that dominate inland. The maximum variance of the seasonal rainfall that could be accounted for by the SST anomalies was about 40%.