Atmosphere Ocean Science Colloquium

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

Speaker: Oliver Watt-Meyer, University of Washington

Location: Warren Weaver Hall 1302

Date: Wednesday, September 26, 2018, 3:30 p.m.

Synopsis:

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.