The Role of Regional Atmospheric Circulation in Shaping Abrupt Climate Reorganization in Africa

Abstract:

During the late Pleistocene and early to mid-Holocene, northern Africa experienced sufficient rainfall to support annual vegetation and widespread lakes. This humid climate state is known as the African Humid Period (AHP). Geologic evidence suggests that the transitions into and out of the AHP occurred rapidly, potentially within a span of decades to centuries. Despite considerable effort to understand the response of precipitation during the AHP, the mechanisms by which the abrupt climate transitions over Africa occurred remain unclear. Here, we use an ensemble of coupled earth system model experiments to explore the role of regional and synoptic-scale atmospheric circulation in Africa during the AHP. Specifically, we analyze characteristics of transient, synoptic-scale weather systems and quantify the relationship between these systems and rainfall in Africa. Preliminary results show that orbital forcing-driven changes in insolation during the AHP weaken surface meridional temperature gradients over Africa and modify the characteristics and energetics of synoptic-scale phenomena, including African easterly waves (AEWs). These results indicate a potential shift in the atmospheric processes that influence precipitation between humid and arid states in northern Africa. We explore whether the insolation-driven changes in local atmospheric processes, in particular the changes in AEWs, contribute to rapid climate reorganization in Africa.