Stratospheric and Tropical Influences on the Mid-Latitude Circulation Response to Rising Greenhouse Gases

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This project seeks to understand how increases in global-mean temperature due to rising greenhouse gas concentrations will affect the jet stream and storm tracks (the typical paths of midlatitude frontal systems) found in the midlatitudes of the Northern and Southern Hemisphere. Previous studies of global warming simulations have found that jet streams and storm tracks in both hemispheres shift towards their respective poles with rising temperature, but the dynamical mechanisms for the shifts are not well understood. Moreover, simulations from different models do not agree as to the magnitude of the shifts. One issue addressed in this project is the role of stratospheric dynamics in producing the shifts (particularly in the Northern Hemisphere), and the extent to which enhanced representation of the stratosphere (more levels in the stratosphere on the model computational grid, for instance) leads to qualitative differences in the shifts. A second issue addressed is the extent to which the jet and storm track shifts in the Southern Hemisphere are influenced by tropical processes.The broader impacts of the work come from the practical value of an improved understanding of the atmospheric circulation response to greenhouse gas-induced warming. Shifts in the jet streams and storm tracks can affect regional climate in the midlatitude, and poleward shifts may lead to widening of the dry subtropical subsidence belts. The project also seeks to understand differences in circulation change from different models, and may help to reduce uncertainty in projections of future climate change. In addition, the work will support and train a graduate student, thereby providing for the future work force in this area.