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SUMMARY:Understanding climate model biases in Southern Hemisphere mid-lati
 tude variability. - Dr Isla Simpson\, Department of Physics\, University o
 f Toronto
DTSTART:20120523T120000Z
DTEND:20120523T130000Z
UID:TALK38072@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:The Southern Annular Mode (SAM) represents a latitudinal shift
 ing of the\nSouthern Hemisphere (SH) jet stream and is the dominant mode o
 f\nvariability in the SH mid-latitude circulation.  A common bias among\ng
 lobal climate models is that they tend to exhibit SAM variability that is 
 much too persistent\, particularly in the summer season.  Many climate\nfo
 rcings such as ozone depletion/recovery and increasing greenhouse gas\ncon
 centrations result in tropospheric circulation changes that project\nstron
 gly onto the SAM and therefore the inability of models to simulate\nnatura
 l SAM variability correctly is of concern for the ability of such\nmodels 
 to accurately predict future circulation changes.\n\nHere\, specifically t
 argetted experiments with one global climate model\,\nthe Canadian Middle 
 Atmosphere Model (CMAM)\, will be used to investigate\nthe cause of this b
 ias in SAM variability.  The role of biases in\nstratospheric variability 
 and climatological tropospheric jet structure\nwill be assessed.  It is fo
 und that even in the absence of stratospheric\nvariability the SAM timesca
 les are biased long relative to the\nobservations\, suggesting a role for 
 a bias in internal tropospheric\ndynamics.  Furthermore\, it is found that
  this bias is not alleviated when the climatological tropospheric jet stru
 cture is improved in an artificial way.  An analysis of tropospheric eddy 
 feedbacks reveals a difference in the strength of planetary scale feedback
 s on the SAM between the model and observations.
LOCATION:Centre for Mathematical Sciences\, meeting room MR14
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