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| Titel |
Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF6 and CO2 |
| VerfasserIn |
H. Bönisch, A. Engel, J. Curtius, Th. Birner, P. Hoor |
| 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 ; 9, no. 16 ; Nr. 9, no. 16 (2009-08-19), S.5905-5919 |
| Datensatznummer |
250007576
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| Publikation (Nr.) |
 copernicus.org/acp-9-5905-2009.pdf |
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| Zusammenfassung |
| The seasonality of transport and mixing of air into the lowermost
stratosphere (LMS) is studied using distributions of mean age of air and a
mass balance approach, based on in-situ observations of SF6 and
CO2 during the SPURT (Spurenstofftransport in der Tropopausenregion,
trace gas transport in the tropopause region) aircraft campaigns. Combining
the information of the mean age of air and the water vapour distributions we
demonstrate that the tropospheric air transported into the LMS above the
extratropical tropopause layer (ExTL) originates predominantly from the
tropical tropopause layer (TTL). The concept of our mass balance is based on
simultaneous measurements of the two passive tracers and the assumption that
transport into the LMS can be described by age spectra which are
superposition of two different modes. Based on this concept we conclude that
the stratospheric influence on LMS composition is strongest in April with
extreme values of the tropospheric fractions (α1) below 20%
and that the strongest tropospheric signatures are found in October with
α1 greater than 80%. Beyond the fractions, our mass balance
concept allows us to calculate the associated transit times for transport of
tropospheric air from the tropics into the LMS. The shortest transit times
(<0.3 years) are derived for the summer, continuously increasing up to
0.8 years by the end of spring. These findings suggest that strong
quasi-horizontal mixing across the weak subtropical jet from summer to mid
of autumn and the considerably shorter residual transport time-scales within
the lower branch of the Brewer-Dobson circulation in summer than in winter
dominates the tropospheric influence in the LMS until the beginning of next
year's summer. |
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