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Quantification of isentropic water‐vapour transport into the lower stratosphere
Author(s) -
Dethof A.,
O'Neill A.,
Slingo J. M.,
Berrisford P.
Publication year - 2000
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712656611
Subject(s) - stratosphere , extratropical cyclone , northern hemisphere , climatology , atmospheric sciences , environmental science , tropopause , troposphere , water vapor , isentropic process , southern hemisphere , geology , meteorology , geography , physics , thermodynamics
The contour advection technique is used to quantify the quasi‐horizontal isentropic transport of water vapour across the tropopause between the tropical upper troposphere and the extratropical lower stratosphere. The calculations are based on European Centre for Medium‐Range Weather Forecasts analyses for 1997 and 1998. It is found that the isentropic transport of water vapour into the extratropical lower stratosphere has a similar magnitude to the upward (cross‐isentropic) transport of water vapour into the stratosphere in the tropics. The isentropic flux is largest during summer, and is more than enough to account for the observed summertime increase in specific humidity in the lowermost stratosphere. The annual isentropic moisture transport into the extratropical lower stratosphere in the northern hemisphere is about one order of magnitude larger than that in the southern hemisphere. This difference in transport explains why the extratropical lower stratosphere is moister in the northern hemisphere during northern summer than it is in the southern hemisphere during southern summer. The results further show that there was more moisture transport into the lower stratosphere of both hemispheres during 1998, under El Niño conditions, than during 1997.