The overall goal of this project is to further our understanding of the factors that govern rainfall and its interannual variability in western equatorial Africa. The work will focus on the mean climate and general circulation in the region, the African Easterly Jet of the Southern Hemisphere, wave activity, mesoscale convective systems, and interannual variability. It will be primarily observational. A pervasive theme is the role of topography. The role of El Niño-Southern Oscillation (ENSO) and the Atlantic will also be emphasized as possible factors in interannual variability. The significance of this work is that it will help to fill in two major gaps in our understanding of African meteorology. One is the knowledge gap concerning its equatorial sector. The other gap is the "black box" of atmospheric circulation that transmits the influence of sea surface temperatures (SSTs) to African rainfall variability.
This work will have many broader impacts. The knowledge generated will provide a basis for studying equatorial processes on a global basis. The results of this study can potentially benefit society via their application to understanding/forecasting of droughts and floods in Africa. Also, this region is the source of water for many semi-arid regions. A better understanding of regional meteorology will have implications for water supply in these adjacent regions. In addition, the project will also have educational impacts on under-represented groups.
, a region about which little had been previously known. The region is of interest because it is the site of the world's most intense storms and Africa is the largest equatorial land mass in the global tropics. Our work identified the mechanisms of the year-to-year variations in rainfall in this region, tying it to global phenomena such as sea-surface temperatures in the global oceans and to El Nino. We were also able to document the existence of easterly waves in this region, analogous to the African easterly waves in West Africa that spawn hurricanes in the Atlantic. We tied these waves to the production/location of precipitation. We also found evidence to link these waves to the African Easterly Jet of the Southern Hemisphere, an important feature first documented by the P.I.'s previous NSF study. We also demonstrated the existence of a low-level coastal jet that may have important implications for climate variability here and elsewhere. We further showed that the major circulation changes associated with rainfall variability in western equatorial Africa are the tropical easterly jet and the low-level equatorial westerly jet. Broader Implications: The last finding complements that of a prior NSF project and demonstrates the need for a whole new paradigm in understanding rainfall variability over Africa. Previously, surface features such as the ITCZ or low-level moisture advection were emphasized. These projects showed instead that the key to understanding variability lies in the upper-level atmospheric circulation, particularly various jet streams and equatorial cells of vertical overturning of wind. Our results can potentially be applied to the understanding and forecasting of droughts and floods in Africa, especially Sahelian West and the Horn of Africa, which has recently been devastated by drought and famine. Also, the region studied in this project is the source of water in many semi-arid regions. For example, rivers originating here flow into Lake Chad and the Okavango Delta. Eventual predictability of interannual and seasonal variability will help predict the availability of these water resources. The project results were integrated into education via graduate teaching, advising, and textbook writing.
