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SUMMARY:Variability and trend in the Brewer-Dobson circulation - Howard Ro
 scoe\, British Antarctic Survey
DTSTART:20100317T140000Z
DTEND:20100317T150000Z
UID:TALK23809@talks.cam.ac.uk
CONTACT:Tracy Moffat-Griffin
DESCRIPTION:The Brewer-Dobson circulation carries trace gases\, including 
 CFCs and greenhouse gases\, from the troposphere to stratosphere\, and fro
 m equator to pole in the stratosphere.  It is wave driven\, and global mod
 els predict its speed to increase in the 21st century due to the action of
  increased greenhouse gases on temperature structure.  Changes in its spee
 d can be deduced from changes in the stratospheric NOy (produced by photo-
 oxidation of the N2O that originates in the troposphere).  We analyse NO2 
 measurements from 1990 to 2007 made by a zenith-sky spectrometer in the An
 tarctic\, and use a photochemical model to improve their accuracy and to d
 educe NOy from the observed NO2.  We focus on NO2 in summer because the ra
 tio of NO2 to NOy is then least affected by stratospheric volcanic aerosol
 .  The NO2 and NOy have large inter-annual variability\, and a broad maxim
 um in 2000-2001\, with little overall trend.  The patterns of variability 
 signify similar changes in speed of Brewer-Dobson circulation but with opp
 osite sign - a broad minimum near 2001.  Multiple regressions show:\n - la
 rge correlations with solar and QBO indices\n - an error in trend of ±3.5
  %/decade\, not yet precise enough to constrain global models\n - an unexp
 lained cycle of amplitude 15% and period >17 years.\n
LOCATION:British Antarctic Survey\, Room 187
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