A New Look at the Seasonal Cycle of Rainfall in East Africa

The seasonal cycle of rainfall over East Africa is typically described as a bimodal rainy season created by the twice-equatorial transit of the ITCZ. This paradigm persists, despite the fact that it is long believed to be wrong be meteorologists working in Africa. This paper re-examines the seasonal cycle over East Africa and shows the fallacy of this scenario. It also describes several factors that do play a role in driving the seasonal cycle. One of these is the low-level Turkana Jet, which appears to have a major influence on rainfall in the region. It is a major factor in the region's prevailing aridity, in interannual variability, and in the lack of a boreal summer rainy season. Understanding the factors controlling the intensity of this jet stream is critical to projecting future climate in the region.