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SUMMARY:The Role of Stratospheric Polar Vortex Breakdown in Southern Hemis
 phere Climate Trends - Gang Chen\, Cornell University\, NY\, United States
DTSTART:20140724T100000Z
DTEND:20140724T110000Z
UID:TALK53369@talks.cam.ac.uk
CONTACT:Dr Scott Hosking
DESCRIPTION:Substantial evidence has suggested that the SH summertime circ
 ulation trends over the late twentieth century are primarily caused by the
  anthropogenic Antarctic ozone hole in spring.  These circulation changes 
 are characterized by a strengthening of the circumpolar winds in the lower
  stratosphere and a trend towards the positive Southern Annular Mode (SAM)
  in the troposphere\, associated with a poleward shift of the tropospheric
  eddy-driven jet.\n\n \n\nGiven the complex interplay between chemistry\, 
 radiation\, and dynamics in the tropospheric response to stratospheric ozo
 ne depletion\, the underlying mechanism(s) have not been fully understood.
   Particularly\, the timing of stratospheric final warming (SFW) has been 
 delayed in the reanalysis data.  An examination of several climate model o
 utputs with different climate forcings indicates that climate trends appea
 r when there is a delay in the timing of SFWs. \n\n \n\nThe role of the SF
 W is examined using an idealized model of stratosphere and troposphere cou
 pling\, in which the ozone depletion is mimicked by a springtime polar str
 atospheric cooling.  The responses of zonal-mean atmospheric circulation i
 n the idealized model are similar to the observed climate trends.  The yea
 rs are further divided into those in which the SFW is delayed and those in
  which it is not.  The responses for the years in which the SFW is delayed
  are very similar to the overall response\, while the stratosphere is only
  characterized by the localized cooling for those years in which the SFW i
 s not delayed\, with no subsequent downward influence into the troposphere
 .  This suggests that\, in order to affect the troposphere\, ozone depleti
 on must first delay the SFW so as to induce a deep response in planetary w
 ave drag and the associated eddy-driven circulation.
LOCATION:British Antarctic Survey\, Room 187
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