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.
Date
09.01.2013
Time
13:30 h
Place
- Bundesstr. 53, room 022/023
- Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg
Speaker
Edwin Gerber, Columbia University