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Ann. Geophys., 20, 871-874, 2002
www.ann-geophys.net/20/871/2002/
© European Geosciences Union 2002
Letter to the Editor
Seasonal variations and vertical movement of the tropopause in the UTLS region
K.-Y. Wang1, D. E. Shallcross2, and J. A. Pyle3
1Department of Atmospheric Sciences, National Central University, Chung-Li, Taiwan
2School of Chemistry, University of Bristol, BS8 1TS, UK
3Centre for Atmospheric Science, Cambridge University, CB2 1EW, UK
Correspondence to: K.-Y. Wang
(kuoying@mail.atm.ncu.edu.tw)
Abstract. Based on the tracking of
the movement of the tropopause over the whole year, the extent/depth of
stratosphere-troposphere exchange (STE) events and their seasonal variations is
investigated. It is found that a stratospheric signature can be observed at
pressures as high as 400 hPa in a hemisphere during its winter to spring
period, while a tropospheric signature can be observed at pressures as low as
190 hPa during the hemispheric summer to autumn months. The major implication
for such a pronounced vertical movement is that the downward penetration of air
from the stratosphere is likely to deposit elevated levels of O3
into the upper troposphere. Though the analysis at 250 hPa reveals that the
values of the stratosphere-troposphere index are similar all year round, a
result which is consistent with other studies, it is found that an intrusion
from the stratosphere to the troposphere is more likely to occur during the
hemispheric winter to spring period than other seasons.
Key words. Atmospheric composition
and structure (pressure, density, and temperature; troposphere–composition
and chemistry)
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