A GCM STUDY OF THE TELECONNECTIONS BETWEEN THE CONTINENTAL CLIMATE OFAFRICA AND GLOBAL SEA-SURFACE TEMPERATURE ANOMALIES

In this case study the role of global SST anomaly forcing in promoting the extreme climatic conditions that prevailed in Africa during the y ears of 1950 and 1973 is examined, In 1950 abundant rainfall was obser ved over tropical Africa, particularly over the Sahel and Southern Afr ica, ay contrast, in 1973, this rainfall anomaly pattern was character ized by the opposite phase, with most of the continent experiencing se vere droughts. The primary research vehicle in this investigation is t he standard version of the NCAR CCMl GCM with horizontal resolution of rhombodial spectral truncation at wavenumber 15 (R15),Two separate 10 -yr simulations based on the 1950 and 1973 observed sea surface temper ature (SST) have been performed. The empirical orthogonal functions me thod is employed to isolate the annual cycle harmonics in the data and also to remove statistical noise, The filtered seasonal rainfall fiel ds for the model and the observations are compared to investigate the response of the African continental climate to the 1950 and 1973 SST c limatologies, CCMl successfully simulates the primary features of the seasonal mean climate conditions and anomalies over the Sahel and Sout hern Africa, The authors attribute this to the ability of the model to simulate the annual harmonic oscillation realistically. Over equatori al Africa, where the semiannual oscillation is:observed to be relative ly more important than it is at the higher latitudes of the continent, the model simulation is not as successful, This occurs because of the deficient simulation of the semiannual harmonic oscillation by the mo del, A weaker annual cycle comprising: the annual mean (nonoscillating component) and the annual harmonic oscillation in tl-ie 1973 Nn relat ive to the 1950 experiment provides a viable explanation for tile sync hronous climatic anomaly conditions that prevailed in northern and sou thern Africa cl;ring these two years. Investigation of the relative ro le of the GCM's internal variability and the SST externally forced var iability during the rainy season over tropical Africa yields valuable insight into the reasons for the observed anomalous climatic behavior. Over the Sahel and Southern Africa, where the annual harmonic oscilla tion is relatively large, externally forced SST variability dominates over internal variability in explaining the drier conditions in 1973 r elative to 1950.