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| Titel |
The relationship between tropospheric wave forcing and tropical lower stratospheric water vapor |
| VerfasserIn |
S. Dhomse, M. Weber, J. Burrows |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 3 ; Nr. 8, no. 3 (2008-02-05), S.471-480 |
| Datensatznummer |
250005539
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| Publikation (Nr.) |
 copernicus.org/acp-8-471-2008.pdf |
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| Zusammenfassung |
| Using water vapor data from HALOE and SAGE II, an anti-correlation
between planetary wave driving (here expressed by the mid-latitude
eddy heat flux at 50 hPa added from both hemispheres) and tropical
lower stratospheric (TLS) water vapor has been obtained. This
appears to be a manifestation of the inter-annual variability of the
Brewer-Dobson (BD) circulation strength (the driving of which is generally measured in terms of the mid-latitude
eddy heat flux), and hence amount of water vapor
entering the stratosphere. Some years such as 1991 and
1997 show, however, a clear departure from the anti-correlation
which suggests that the water vapor changes in TLS can not be
attributed solely to changes in extratropical planetary wave activity (and its effect on the BD circulation). After
2000 a sudden decrease in lower stratospheric water vapor has been
reported in earlier studies based upon satellite data from HALOE,
SAGE II and POAM III indicating that the lower stratosphere has
become drier since then. This is consistent with a sudden rise in
the combined mid-latitude eddy heat flux with nearly equal
contribution from both hemispheres as shown here and with the
increase in tropical upwelling and decrease in cold point
temperatures found by Randel et al. (2006). The low water vapor
and enhanced planetary wave activity (in turn strength of the BD circulation) has persisted until the
end of the satellite data records. From a multi-variate regression
analysis applied to 27 years of NCEP and HadAT2 (radiosonde) temperatures (up to
2005) with contributions from solar cycle, stratospheric
aerosols and QBO removed, the enhancement wave driving after 2000 is
estimated to contribute up to 0.7 K cooling to the overall TLS
temperature change during the period 2001–2005 when compared to the
period 1996–2000. NCEP cold point temperature show an average
decrease of nearly 0.4 K from changes in the wave driving, which is
consistent with observed mean TLS water vapor changes of about −0.2 ppm after 2000. |
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