Joint Seminar: Modeling the Extratropical Jets: Connections between the mean climate, variability, and response to anthropogenic forcing

The poleward expansion of the midlatitude jets streams and storm tracks is

perhaps the most robust response of the extratropical atmospheric

circulation to anthropogenic forcing.  While the synoptic scale dynamics

of the midlatitude atmosphere are fairly well represented in coupled

climate models in comparison to other critical processes that can only

parameterized at current resolution, recent studies have shown that the

large scale circulation is not yet a solved problem. Trends in both

hemispheres have been shown to be sensitive to upper atmospheric

processes, particularly for the Southern Hemisphere due to stratospheric

ozone loss.  Over the past four decades, greenhouse gas induced tropical

tropospheric warming and ozone induced cooling of the stratosphere have

worked in concert, pushing and pulling the austral jet stream poleward. 

In the future, with the expected recovery of the ozone layer, the two

process will oppose each other, necessitating a more careful understanding

of the balance in forcings.  In addition, the sensitively of the

midlatitude atmosphere to climate forcing in models appears to be related

to biases in the mean climate and internal variability; models tend to

place the jet streams to equatorward, and models with a larger equatorward

bias respond more strongly to all climate forcings.  The link between

biases in the mean climate and the time scales of internal variability

suggest that these errors may be associated with a misrepresentation of

eddy-mean flow coupling in comprehensive models, and ideas from

fluctuation-dissipation theory could help explain differences in the

sensitivity to climate forcings.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Edwin Gerber, Columbia University


Hauke Schmidt

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