Mesoscale Modeling of Tropical Paleoclimate

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This award will serve to develop and apply a mesoscale modeling system for studying past variability in tropical climates of Africa and South America during the Last Glacial Maximum (LGM). The modeling system consists of two models. A mesoscale climate model (MCM) will simulate climate on space scales of tens of kilometers. A general circulation model (GCM) will generate lateral boundary conditions on wind, temperature, and moisture for the mesoscale model. Simulations of the dry climates of the present day and LGM (~21,000 years ago) over northern Africa will be contrasted with simulations for the African Humid Period, approximately 6,000 years ago when Sahelian and Saharan Africa supported numerous lakes and extensive vegetation. The research will address the following questions:-What are the individual and combined roles of insolation, changes in land surface conditions, regional SST differences, and differences in large-scale climate (i.e., MCM lateral boundary conditions) in causing differences in surface wetness over northern Africa among the present day, African Humid Period and the LGM?-Are the differences in wetness associated with changes in precipitation only, or do changes in evaporation and/or water table levels play an important role?-What mechanisms are involved in changing the atmospheric column water vapor budget? -Are any important mechanisms nonlinear in a way that helps explain the speed with which the climate can change in this region? What are the implications for future climate change (global warming)?Simulations with various combinations of lateral and surface boundary conditions, as well as other forcing functions such as insolation and atmospheric composition, will identify the important factors and physical mechanisms that lead to the wet conditions and the rapid climate change that is hypothesized to have occurred in Amazonia during the Holocene. The mesoscale modeling system will also be used to study South American climate of the LGM.The research will address the following questions:-What was the distribution of drying and cooling during the LGM in the Amazon Basin and what mechanisms are associated with the differences from the present day climate?-What differences in aridity in the Central Andes are simulated with the MCM, and what mechanisms account for differences from the present day?-How are the simulated differences in both regions related to global-scale climate conditions and how are they linked?-Does the model support the idea that there are different aridity trends in different areas of the high Central Andes? If so, are these trends providing information about inter-hemispheric symmetry or asymmetry of climate change during the last glacial cycle?