College of Liberal Arts

The Evolution of the North American Monsoon: Perspectives from Proxies and Models

Friday Mar 24, 2017 3:00 PM - 4:00 PM | CLA 0.128

By Dr. Tripti Bhattacharya, University of California, Berkeley

The North American Monsoon, or NAM, provides necessary water resources and sustains unique, biodiverse ecosystems in the US Southwest and western Mexico. Despite its critical importance to regional hydrology, the fundamental mechanisms that shape this monsoon remain poorly understood. Some researchers emphasize the importance of oceanic conditions in driving NAM variability, while others emphasize the large-scale atmospheric flow or changes on the land surface. In this talk, I analyze NAM changes during the Last Glacial Maximum, or LGM (~18 to 21 ka BP). The dramatic departures from pre-industrial boundary conditions at the LGM offer a natural ‘experiment’ for evaluating different theories about the fundamental dynamics that shape the NAM. Using new paleoclimatic records of the NAM and a suite of experiments of a coupled atmosphere-ocean general circulation model (AO-GCM), I provide novel evidence about the mechanisms that drove weakening of the NAM at the LGM. Proxy and model evidence suggest that LGM monsoon weakening was driven by ice sheet-induced changes in the atmospheric circulation, which brought anomalous cold, dry air into the monsoon region. This worklinks our understanding of the NAM to broader theories of monsoon dynamics, with important implications for understanding its present climatology and future behavior.

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