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| Titel |
The impact of tropical recirculation on polar composition |
| VerfasserIn |
S. E. Strahan, M. R. Schoeberl, S. D. Steenrod |
| 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. 7 ; Nr. 9, no. 7 (2009-04-03), S.2471-2480 |
| Datensatznummer |
250007163
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| Publikation (Nr.) |
 copernicus.org/acp-9-2471-2009.pdf |
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| Zusammenfassung |
| We derive the tropical modal age of air from an analysis
of the water vapor tape recorder. We combine the observationally derived
modal age with mean age of air from CO2 and SF6 to create
diagnostics for the independent evaluation of the vertical transport rate
and horizontal recirculation into the tropics between 16–32 km. These
diagnostics are applied to two Global Modeling Initiative (GMI) chemistry
and transport model (CTM) age tracer simulations to give new insights into
the tropical transport characteristics of the meteorological fields from the
GEOS4-GCM and the GEOS4-DAS. Both simulations are found to have modal ages
that are in reasonable agreement with the empirically derived age (i.e.,
transit times) over the entire altitude range. Both simulations show too
little horizontal recirculation into the tropics above 22 km, with the
GEOS4-DAS fields having greater recirculation. Using CH4 as a proxy for
mean age, comparisons between HALOE and model CH4 in the Antarctic
demonstrate how the strength of tropical recirculation affects polar
composition in both CTM experiments. Better tropical recirculation tends to
improve the CH4 simulation in the Antarctic. However, mean age in the
Antarctic lower stratosphere can be compromised by poor representation of
tropical ascent, tropical recirculation, or vortex barrier strength. The
connection between polar and tropical composition shown in this study
demonstrates the importance of diagnosing each of these processes separately
in order to verify the adequate representation of the processes contributing
to polar composition in models. |
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