The project will use both numerical experiments and observational analyses to investigate two unsolved questions in the field of climate dynamics: 1) what physical mechanisms drive the tropospheric response to extratropical stratospheric variability? and 2) through what processes do anthropogenic emissions of carbon dioxide and ozone depleting gases drive large-scale changes in the extratropical circulation?
In the modeling component, the investigators will examine and diagnose the simple general circulation model response to spatially varying thermal forcings which mimic the radiative responses to increasing atmospheric carbon dioxide and stratospheric ozone depletion/recovery. The experiments will be used to 1) assess the circulation responses to thermal forcings at tropospheric and stratospheric levels; 2) assess the robustness of the responses to changes in the shape and amplitude of the forcings and to changes in the model climatology; and 3) investigate the physical mechanisms that drive the simulated responses. In the observational component, the investigators will conduct analyses that 1) complement the numerical experiments, and 2) investigate the processes associated with recent stratospheric climate change. The observational analyses will provide a "reality-check" for the model experiments, new analyses of the daily evolution of the heat and momentum fluxes associated with stratosphere/troposphere coupling, and new analyses of the linkages between tropical tropospheric heating and variability in the extratropical flow.
The broader impacts of this work include implications for weather forecasting (via stratosphere/troposphere coupling), for the attribution of past climate trends, and for the prediction of future changes in the circulation in response to anthropogenic forcing. This project will train and support one postdoctoral researcher and two graduate students.
The intellectual merit of the project was to improve our understanding of large-scale climate variability. Specific emphases of the research included: 1) the diagnosis and analysis of the processes whereby stratospheric variability influences the troposphere; 2) the diagnosis and analysis of the physical processes whereby anthropogenic forcing influences the extratropical atmospheric circulation; 3) the interpretation of observed climate change; and 4) exploring the dynamics of large-scale variations in extratropical climate. The award provided support for 22 research papers on various aspects of large-scale climate variability. The results have improved our understanding of the atmospheric response to anthropogenic climate change. They have provided novel evidence of abrupt changes in ocean temperatures during the 20th century, led to improved understanding of the role of the stratosphere in weather forecasts, and demonstrated the potential importance of sea-ice changes for midlatitude weather. The results have led to advances in our understanding of the role of clouds in climate variability, the role of ozone depletion in observed climate change, and the importance of equatorial waves in tropical climate variability. Papers written under the auspices of the grant have also identified key mysteries in recent stratospheric climate change, provided evidence that large scale variability in the stratospheric circulation perturbs tropospheric clouds, and provided evidence for a novel form of climate variability that has implications for weather across much of the Southern Hemisphere. The broader impacts of the proposed research include implications for weather forecasting, for the attribution of past climate trends, and for the prediction of future changes in the circulation in response to anthropogenic forcing. The broader impacts also include postdoctoral and graduate education and thus the mentoring of next generation of climate scientists. It provided partial or full support for 2 PhD theses, 2 MS theses, and 2 current graduate students. It also provided partial support for a postdoctoral researcher.
