A Significant body of empirical studies indicated that continental-scale climate anomalies play an important part in determining the variability of the African climate. One of these decadal-scale climate anomaly regimes concerns the simultaneous phase reversal, in the precipitation anomaly distribution, between equatorial and tropical Africa. This continental-scale concurrence happens despite the fact that the rainy season in each latitudinal band over the continent comes at different phases of the annual cycle. Clearly, a continental-scale teleconnection mechanism appears to be involved in the development and maintenance of these climatic conditions. The PI's solutions obtained form a steady-state multi-level linear model, indicate that the interaction between the large-scale African orography and the climatic fluctuations in the basic state could help to produce the observed teleconnections in the African climate. The PI will extend his previous investigations by performing a series of numerical simulations based on the NCAR Community Climate Model (CCM). This investigation will be aimed at two distinct but closely related and complementary objectives which may be stated as follows. (1) Employ the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) to investigate the observed three-way connection between the global sea surface temperature (SST), the continental-scale teleconnections in the African climate, and the regional Sahelian droughts. The numerical integrations will be based on two versions of the NCAR GCM, an earlier model designated CCM1, and a new version CCM2, in which extensive enhancements have been implemented. (2) Introduce and test a new hypothesis concerning the role of the interaction between the large-scale orography of Africa and the mean zonal flow in promoting the observed teleconnections in the African climate. Through this investigation the PI hopes to clarify some of the important physical mechanisms responsible for the continental- scale teleconnections in the African climate. In addition this study will help to assess the relative performances of CCM1 and CCM2 in simulating the variability of the tropical climate, thus contributing toward further improvements in the models.
