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SUMMARY:Variability in upwelling in the tropical lower stratosphere: effec
 ts on tracers and dynamical forcing - Marta Abalos (Laboratoire de Météo
 rologie Dynamique (CNRS/IPSL))
DTSTART:20140604T143000Z
DTEND:20140604T153000Z
UID:TALK52763@talks.cam.ac.uk
CONTACT:Dr Amanda Maycock
DESCRIPTION:The zonal mean mass circulation of the stratosphere (the Brewe
 r-Dobson circulation) is characterized by upwelling in the tropics and dow
 nwelling at high latitudes. The slow ascent across the tropical tropopause
  largely controls the composition of air entering the stratosphere. Despit
 e its relevance\, tropical upwelling is poorly constrained by observations
  and its magnitude\, variability and specific forcing remain uncertain.\n\
 nThe variability in upwelling can especially influence tracers with steep 
 vertical gradients across the tropical tropopause\, such as ozone and carb
 on monoxide. Satellite observations of these tracers are used to examine t
 he relation with indirect estimates of tropical upwelling based on reanaly
 sis data. Complementary analyses using the Whole Atmosphere Community Clim
 ate Model allow explicitly evaluating the effect of eddy transport on trac
 er variability\, in addition to upwelling. The large annual cycle observed
  in the tracers and in temperature in the tropical lower stratosphere is m
 ainly linked to upwelling\, while eddy transport is important around the t
 ropopause.\n\nIn addition to the annual cycle\, the upwelling estimates an
 d the tracers show substantial coherent fluctuations on sub-seasonal times
 cales\, and the specific dynamical forcing of such variability is investig
 ated. The statistical patterns obtained in the reanalysis manifest the res
 ponse of the zonal mean circulation extending away from the transient forc
 ing regions\, as expected from theory. Sub-seasonal variability in upwelli
 ng is mostly linked to wave drag in the extratropical winter stratosphere 
 and the subtropical upper troposphere\, with stronger effects on the deep 
 and the shallow branches of the Brewer-Dobson circulation\, respectively.\
 n
LOCATION:Unilever  Lecture Theatre\,  Department of Chemistry
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