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| Titel |
Forecasted deep stratospheric intrusions over Central Europe: case studies and climatologies |
| VerfasserIn |
T. Trickl, H. Feldmann, H.-J. Kanter, H.-E. Scheel, M. Sprenger, A. Stohl, H. Wernli |
| 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 ; 10, no. 2 ; Nr. 10, no. 2 (2010-01-20), S.499-524 |
| Datensatznummer |
250007958
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| Publikation (Nr.) |
 copernicus.org/acp-10-499-2010.pdf |
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| Zusammenfassung |
| Based on daily predictions of stratospheric air intrusions, obtained from
trajectory calculations by ETH Zürich with wind fields from ECMWF
forecasts, a high number of measurements with the ozone lidar at IMK-IFU
(Garmisch-Partenkirchen, Germany) were carried out in 2001. The lidar
measurements show a large variety of rather different cases reflecting the
full complexity of intrusion episodes that is not visible in classical case
studies. In part, tropopause folds could be fully captured. The frequency of
intrusion cases forecasted and verified by vertical sounding or in the
in-situ data recorded at the nearby Zugspitze summit (2962 m a.s.l.) exceed
that in previous work by more than a factor of two. Three cases mapped with
the lidar were selected to validate the results for the corresponding time
periods extracted from a one-year run with the new hemispheric version of the
chemistry-transport model EURAD. Due to the high spatial resolution chosen
for these simulations the agreement with the lidar measurements is
satisfactory. The Zugspitze ozone data from 1978 to 2004 were recently
filtered by applying different criteria for stratospheric air, based on the
7Be and humidity measurements. Here, by using the daily model forecasts
during the time period 2001–2005, we examine three criteria and determine
how well they represent the stratospheric air intrusions reaching the
mountain site. Seasonal cycles for the period 2001–2005 were derived for the
forecasts as well as the intrusion frequency per month for the forecasted
intrusions and each of the criteria, distinguishing eight different
characteristic transport pathways. In most cases a winter maximum and a
summer minimum was obtained, but in the case of cyclonic arrival of
intrusions starting over Greenland a late-spring maximum is seen. Two of the
filtering criteria examined, based on combining a relative-humidity (RH)
threshold of 60% with either a 7Be threshold of 5.5 mBq m−3 or
the requirement for RH≤30% within ±6 h, rather reliably predict
periods of deep intrusions reaching the Zugspitze station. An "or"
combination of both these criteria yields slightly more cases and covers
77.9% of the intrusions identified. The lack of observations in the
complementary 22.1% are mostly explained by overpasses. In this way the
long-term trend of stratospheric ozone observed at this site as well as the
corresponding ozone budget may be derived on the basis of measurements only.
This effort will be the subject of a subsequent publication. |
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