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SUMMARY:The annual cycle in tropical lower stratospheric temperatures - Dr
  Alison Ming\, Cambridge University
DTSTART:20160516T131500Z
DTEND:20160516T141500Z
UID:TALK65024@talks.cam.ac.uk
CONTACT:Paul Griffiths
DESCRIPTION:A striking feature of the upper part of the tropical tropopaus
 e layer is that temperatures exhibit a marked annual cycle (rather that th
 e semiannual cycle one might expect from the fact the sun passes over the 
 Equator twice in a year). This temperature cycle has its largest amplitude
  around 70 hPa. Part of the explanation could come from the annual cycle i
 n ozone having a significant radiative influence in this region. We will f
 irst give a brief overview of radiative exchange in the atmosphere with so
 me results from a radiation code set up to do a fixed dynamical heating ca
 lculation. We will then quantify the ozone contribution to the temperature
  using a seasonally evolving fixed dynamical heating (SEFDH) method. We fi
 nd that the ozone cycle produces an annual cycle in temperature that is co
 nsistent with previous work and also argue that water vapour has a non-neg
 ligible influence. We also quantify the relative influences of water vapou
 r and ozone on temperatures in the region below the cold point at 100 hPa.
  The SEFDH approach is limited by the fact that the feedbacks on temperatu
 re arising from circulation changes cannot be studied. To go beyond SEFDH\
 , experiments are done using an idealised zonally symmetric general circul
 ation model in which the zonally symmetric dynamics in the stratosphere ca
 n respond to the radiative effect of changes in the trace gases. Such a mo
 del has the advantage that the atmosphere can be constrained to only inclu
 de certain aspects of the dynamical and radiative feedback in the stratosp
 here. With an annual cycle in ozone\, the model produces a smaller amplitu
 de annual cycle in temperature with less latitudinal structure than the SE
 FDH calculation.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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