Teleconnections between global sea-surface temperatures and the interannual variability of observed and model simulated rainfall over southern Africa

Abstract

Sea-surface temperatures (SSTs) for the thirty-year period 1961–1990 are prescribed as boundary forcing for a series of atmospheric general circulation model (AGCM) experiments. The results of five separate multidecadal AGCM runs, each forced with the same SSTs, but different initial conditions, have been used to form an ensemble. The interannual variability of AGCM simulated rainfall over South Africa and Namibia (southern Africa) are compared with observations. Empirical orthogonal function (EOF) analyses revealed a strong correlation between the dominant observed austral summer season (October–March) and mid-summer season (December and January) rainfall patterns over southern Africa and the corresponding model results. It is shown that the AGCM simulated austral summer season rainfall variability in the dominant amplitude time series (first principle component or PC1 time series) compare well with SST fluctuations over the equatorial Pacific and tropical western Indian Oceans. Although the associated dominant observed rainfall time series accounts for a larger fraction of the total variability (relative to the AGCM), it also compares well with equatorial Pacific and tropical western Indian Ocean SST fluctuations. To a certain degree these results accentuates the model's ability to capture the major summer seasonal rainfall variability as a response of global SST forcing, which might make the AGCM suitable for future use in seasonal rainfall forecasting research. Similar associations could not be found for the austral winter season (May–August).