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SUMMARY:Wave activity\, eddy diffusivity\, and jet variability - Gang Chen
 \, Cornell University
DTSTART:20130711T120000Z
DTEND:20130711T130000Z
UID:TALK46192@talks.cam.ac.uk
CONTACT:9780
DESCRIPTION:Changes in atmospheric compositions (e.g.\, the rising greenho
 use gases\, changes in air pollution or Antarctic ozone hole or recovery) 
 can alter the latitudes of midlatitude jet streams\, and consequently impa
 ct the hydrological cycles. The mechanisms of the circulation changes are 
 studied with both idealized and comprehensive GCMs. Particularly\, althoug
 h El Nino and global warming are both characterized by warming in the trop
 ical  upper troposphere\, the latitudinal changes of mid-latitude eddy-dri
 ven jet are opposite in sign. By comparing the circulation changes to seve
 ral patterns of tropical warmings in a dry atmospheric model\, we will ill
 ustrate the important distinctions between the processes associated with u
 pper-tropospheric baroclinicity and lower-tropospheric baroclinicity. \n\n
 With an initial value approach\, the circulation changes in idealized mode
 ls are compared with classical paradigms of baroclinic eddy life cycles. I
 t is found that while the change in the lower-level baroclinicity is impor
 tant for the (El Nino-like) equatorward contraction in circulation under n
 arrow tropical warming\, the change in the upper-level baroclinicity domin
 ates the (global warming-like) poleward shift in circulation in response t
 o broad tropical warming. Additionally\, it is found that the circulation 
 change be better understood by a hybrid Eulerian-Lagrangian diagnostic tha
 t quantifies the eddy diffusivity change associated with wave breaking in 
 the upper troposphere. The eddy diffusivities in quasi-geostrophic flow an
 d isentropic flow will be also briefly compared.
LOCATION: Centre for Mathematical Sciences\, MR 9
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