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| Titel |
How stratospheric are deep stratospheric intrusions? |
| VerfasserIn |
T. Trickl, H. Vogelmann, H. Giehl, H.-E. Scheel, M. Sprenger, A. Stohl |
| 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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-19), S.9941-9961 |
| Datensatznummer |
250119051
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| Publikation (Nr.) |
 copernicus.org/acp-14-9941-2014.pdf |
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| Zusammenfassung |
| Preliminary attempts of quantifying the stratospheric ozone contribution in the observations at
the Zugspitze summit (2962 m a.s.l.) next to Garmisch-Partenkirchen in the German Alps
had yielded an approximate doubling of the stratospheric fraction of the Zugspitze ozone during
the time period 1978 to 2004. These investigations had been based on data filtering by using low
relative humidity (RH) and elevated 7Be as the criteria for selecting half-hour intervals of
ozone data representative of stratospheric intrusion air. To quantify the residual
stratospheric component in stratospherically influenced air masses, however, the mixing of
tropospheric air into the stratospheric intrusion layers must be taken into account. In fact, the
dewpoint mirror instrument at the Zugspitze summit station rarely registers RH values lower than 10% in stratospheric air intrusions. Since 2007 a programme of routine
lidar sounding of ozone, water vapour and aerosol has been conducted in the Garmisch-Partenkirchen
area. The lidar results demonstrate that the intrusion layers are drier by roughly one order of
magnitude than indicated in the in situ measurements. Even in thin layers RH values
clearly below 1% have frequently been observed. These thin, undiluted layers present an
important challenge for atmospheric modelling. Although the ozone values never reach values
typical of the lower-stratosphere it becomes, thus, obvious that, without strong wind shear
or convective processes, mixing of stratospheric and tropospheric air must be very slow in
most of the free troposphere. As a consequence, the analysis the Zugspitze data can be assumed to be more reliable
than anticipated. Finally, the concentrations of Zugspitze carbon monoxide rarely drop inside
intrusion layers and normally stay clearly above full stratospheric values. This indicates that
most of the CO, and thus the intrusion air mass, originates in the shallow "mixing layer" around
the thermal tropopause. The CO mixing ratio in these descending layers between 1990 and 2004
exhibits a slightly positive trend indicating some Asian influence on the lowermost stratosphere
in the high-latitude source region of most intrusions reaching the station. |
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