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SUMMARY:Variability of the polar stratospheric vortex and its impact on su
 rface climate patterns - Aditi Sheshadri\, Columbia University
DTSTART:20160121T141500Z
DTEND:20160121T151500Z
UID:TALK62898@talks.cam.ac.uk
CONTACT:Paul Griffiths
DESCRIPTION:The seasonal variability of the polar stratospheric vortex is 
 studied in a simplified AGCM driven by specified equilibrium temperature d
 istributions. Seasonal variations in equilibrium temperature are imposed i
 n the stratosphere only\, enabling the study of stratosphere–troposphere
  coupling on seasonal time scales\, without the complication of an interna
 l tropospheric seasonal cycle. The model is forced with different shapes a
 nd amplitudes of simple bottom topography\, resulting in a range of strato
 spheric climates. Hemispheric differences in stratospheric seasonal variab
 ility are recovered in the model with appropriate choices of wave-2 topogr
 aphy. In the model experiment with a realistic Northern Hemisphere–like 
 frequency of stratospheric sudden warming events\, the distribution of the
  intervals between these events suggests that the model has no year-to-yea
 r memory. In addition to tropospheric impacts of stratospheric ‘events
 ’\, it is shown that there are tropospheric impacts of the stratospheric
  seasonal cycle itself.\n\nAdditionally\, the model is used to investigate
  the sensitivity of model responses to the timing of imposed polar stratos
 pheric cooling\, intended to mimic the radiative effects of ozone depletio
 n. The model exhibits circulation responses to springtime cooling that qua
 litatively match both observations and the responses of comprehensive chem
 istry climate models. The model’s surface response is sensitive to the t
 iming of the cooling\, suggesting that the meteorology plays an important 
 role. The model’s responses are not always annular mode-like. Larger and
  more persistent surface responses at certain times are consistent with th
 e model’s seasonal cycle of tropospheric annular mode timescales. It is 
 shown that lower stratospheric variability impacts the persistence of the 
 tropospheric jet and storm tracks.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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