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| Titel |
Mixing processes and exchanges in the tropical and the subtropical UT/LS |
| VerfasserIn |
R. James, B. Legras |
| 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. 1 ; Nr. 9, no. 1 (2009-01-07), S.25-38 |
| Datensatznummer |
250006627
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| Publikation (Nr.) |
 copernicus.org/acp-9-25-2009.pdf |
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| Zusammenfassung |
Both in situ measurements and satellite observations
indicate evidence of mixing in the upper troposphere (UT) and the
lower-stratosphere (LS). In this study, the measurements performed
during the Pre-AVE and Costa-Rica AVE campaigns are analysed with
diffusive back-trajectories to assess mixing properties in the
tropical and the subtropical UT/LS. A description of
cross-tropopause pathways and mixing time scales is provided.
In the subtropics, Troposphere-Stratosphere mixing processes are
found to differ in the vicinity of the tropopause and at higher
altitudes. Below 350 K, a mixing line observed during Pre-AVE is
shown to result from fast and local cross-tropopause irreversible
exchange, involving two initially distant air masses with distinct
chemical compositions. For measurements located above 350 K, mixing
of the tropospheric air in the subtropical stratosphere occurs over
a period of a month, the origins of the tropospheric source being
localised in the tropical UT and the tropical boundary layer.
In the tropics, quantitative reconstructions of CO and
O3 profiles above 360 K are obtained for one month
back-trajectories calculations, pointing out that long term mixing
is essential to determine the chemical composition in the tropical
ascent. In particular, the existence of two-way meridional
irreversible exchanges between 360 and 450 K is found to export
tropical air in the subtropical stratosphere and to entrain old
stratospheric air in the tropical ascent. Mean age of air
calculated with a Lagrangian model is shown to be in agreement with
the CO2 observations. |
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