In a previous study, the climatological precipitation over South America, particularly the Nordeste region, has been shown to be influenced by the presence of Africa. Here the implications for variability are explored by perturbing the forcing field over Africa in various ways.

The influences of topography and surface conditions over Africa on South American climate are studied by means of an R30 General Circulation Model. Results from four idealized perpetual January experiments, which differ only by the distributions of African topography and soil moisture are discussed. The wind and precipitation field from the most realistic experiment compares reasonably well with the observed climatology.

To investigate its role on South American climate, results of experiments in the presence and absence of African topography are compared. Through its thermal and mechanical interaction with the tropical easterlies, African topography is found to be a significant contributor to the relatively dry conditions over northeastern parts of South America.

The responses of South American precipitation field to wet and dry surface conditions over the Sahel are also analyzed. Wet surface conditions over the later region lead to cross equatorial thermal gradient, southward displacement of the ITCZ and increased precipitation over northeastern parts of South America. The precipitation field over the region is found to be relatively less sensitive to dry surface conditions over tropical Africa.

Moisture,surface heat and vorticity budget analysis and linear theory are used to interpret the above results.