Change in the Extratropical Circulation in Response to Global Warming

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

In simulations of global warming, climate models display robust changes in the global atmospheric circulation. Notable among these is a strengthening and poleward shift of the midlatitude jets. Because these jets are collocated with the midlatitude stormtracks, these shifts imply societally important changes in the distribution of precipitation. While these changes have been documented in many global climate models, a dynamical mechanism has remained elusive, and it remains, therefore, unclear, how much confidence should be placed in them. It has been noted that the simulated changes project strongly on intrinsic modes of unforced variability in the models. The PIs will: . Identify the changes that occur in the extratropical circulations of global models under greenhouse-gas forcing. . Relate the structures of such changes to intrinsic modes of variability of model climates, and to use such relationships to predict what changes are likely to occur in the real atmosphere. . Use experiments with idealized models to isolate those aspects of the response to global warming that lead to the shift in the jets. . Use experiments with the Community Climate System Model (CCSM) to determine the roles of different aspects of climate change in causing the circulation to change. . Use simple dynamical models to understand the mechanisms that drive the circulation changes. Broader impacts of the research are an improved understanding of the credibility of climate-change projections. A graduate student will be trained, and the results of the research will be incorporated in courses taught by the co-investigator.