Dr. Oliver Watt-Meyer, from the University of Washington, will present a talk at the SEAS Colloquium in Climate Science (SCiCS).

Title:
Extratropical circulation response to warming: role of cloud radiative effects and ITCZ width changes

Abstract:
The expected poleward shifts in the Hadley cell edge and eddy-driven jet under climate change will have fundamental impacts on society through changes in the distribution of precipitation and the location of storm tracks. It has been suggested that changes in atmospheric cloud radiative effects under global warming is one of the causes for these shifts. This study examines the Clouds On-Off Klimate Intercomparison Experiment ensemble of aquaplanet simulations to analyze whether the cloud impact on the circulation response to warming is consistent across models. The response of the eddy-driven jet latitude to a globally uniform +4K SST perturbation decreases by about 45% (averaged across models) when cloud radiative effects are turned off, and is also far less consistent between models. The range of responses can be partially explained by appealing to the changes in the inter-tropical convergence zone (ITCZ) width under the +4K SST perturbation. Additional targeted experiments with the GFDL-AM2 model show that narrowing in the width of the ITCZ under global warming in these simulations causes the shift of the Hadley cell edge and eddy-driven jet to be smaller than it would be otherwise.

Biography:
Dr. Watt-Meyer is an NOAA Climate and Global Change Postdoctoral Fellow in the Department of Atmospheric Sciences at the University of Washington. His research is on the dynamics of the large-scale circulation of the atmosphere, with a focus on the extratropics. Broadly speaking, he is motivated by understanding processes that affect the variability of the atmosphere on sub-seasonal to seasonal timescales, as well as the climate change response. These processes include stratosphere-troposphere coupling, the main focus of his Ph.D. thesis, tropical-extratropical teleconnections, and the interaction between cloud radiative effects and the atmospheric circulation. He uses observational data, idealized modelling experiments and analysis of comprehensive climate models as tools for his research.