Atmosphere Ocean Science Colloquium

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Do Mid-Latitude Jet Shifts Cause Cloud Feedbacks?

Speaker: Kevin Michael Grise, University of Virginia

Location: Warren Weaver Hall 1302

Date: Wednesday, April 13, 2016, 3:30 p.m.

Synopsis:

In response to increasing atmospheric greenhouse gas concentrations, most global climate models project that the mid-latitude jet streams will shift poleward over the 21st century. Consequently, the tracks of mid-latitude low-pressure systems and their associated cloud features are also anticipated to shift poleward over this time. As these cloud features move from a lower to a higher latitude, they will move from a latitude of greater incoming solar radiation to one of less incoming solar radiation. Thus, it seems logical to assume that such poleward movement in the clouds will lead to a warming feedback, as the clouds will be reflecting less solar radiation when they move to higher latitudes. In this talk, I will challenge this notion using satellite observations from the NASA CERES mission. By looking at interannual variability in the jet location and cloud-radiative effects, I will show that a poleward jet shift is not associated with cloud-radiative warming in the Southern Hemisphere and is only associated with cloud-radiative warming in some seasons in the Northern Hemisphere. Most global climate models are incapable of capturing these patterns, particularly in the Southern Hemisphere, where many models indicate robust cloud-radiative warming effects with a poleward jet shift. Reasons for these model-observational differences with be diagnosed, and the implications of these model biases for future climate projections will be explored.