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CATEGORIES:British Antarctic Survey
SUMMARY:The Role of Stratospheric Polar Vortex Breakdown i
 n Southern Hemisphere Climate Trends - Gang Chen\,
  Cornell University\, NY\, United States
DTSTART;TZID=Europe/London:20140724T110000
DTEND;TZID=Europe/London:20140724T120000
UID:TALK53369AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/53369
DESCRIPTION:Substantial evidence has suggested that the SH sum
 mertime circulation trends over the late twentieth
  century are primarily caused by the anthropogenic
  Antarctic ozone hole in spring.  These circulatio
 n changes are characterized by a strengthening of 
 the circumpolar winds in the lower stratosphere an
 d a trend towards the positive Southern Annular Mo
 de (SAM) in the troposphere\, associated with a po
 leward shift of the tropospheric eddy-driven jet.\
 n\n \n\nGiven the complex interplay between chemis
 try\, radiation\, and dynamics in the tropospheric
  response to stratospheric ozone depletion\, the u
 nderlying mechanism(s) have not been fully underst
 ood.  Particularly\, the timing of stratospheric f
 inal warming (SFW) has been delayed in the reanaly
 sis data.  An examination of several climate model
  outputs with different climate forcings indicates
  that climate trends appear 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 stratosp
 here and troposphere coupling\, in which the ozone
  depletion is mimicked by a springtime polar strat
 ospheric cooling.  The responses of zonal-mean atm
 ospheric circulation in the idealized model are si
 milar to the observed climate trends.  The years a
 re further divided into those in which the SFW is 
 delayed and those in which it is not.  The respons
 es for the years in which the SFW is delayed are v
 ery similar to the overall response\, while the st
 ratosphere is only characterized by the localized 
 cooling for those years in which the SFW is not de
 layed\, with no subsequent downward influence into
  the troposphere.  This suggests that\, in order t
 o affect the troposphere\, ozone depletion must fi
 rst delay the SFW so as to induce a deep response 
 in planetary wave drag and the associated eddy-dri
 ven circulation.
LOCATION:British Antarctic Survey\, Room 187
CONTACT:Dr Scott Hosking
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