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| Titel |
Evaluation of near-tropopause ozone distributions in the Global Modeling Initiative combined stratosphere/troposphere model with ozonesonde data |
| VerfasserIn |
D. B. Considine, J. A. Logan, M. A. Olsen |
| 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 ; 8, no. 9 ; Nr. 8, no. 9 (2008-05-06), S.2365-2385 |
| Datensatznummer |
250006097
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| Publikation (Nr.) |
 copernicus.org/acp-8-2365-2008.pdf |
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| Zusammenfassung |
The NASA Global Modeling Initiative has developed a combined
stratosphere/troposphere chemistry and transport model which fully
represents the processes governing atmospheric composition near the
tropopause. We evaluate model ozone distributions near the tropopause, using
two high vertical resolution monthly mean ozone profile climatologies
constructed with ozonesonde data, one by averaging on pressure levels and
the other relative to the thermal tropopause. At the tropopause, model ozone is high-biased in
the SH tropics and NH midlatitudes by ~45% in a 4°
latitude ×5° longitude model simulation. Doubling the resolution to
2°×2.5° increases the NH high bias to ~60%,
and reduces the tropical bias to ~30%, apparently due to
decreased horizontal transport between the tropics and extratropics in the
higher-resolution simulation. These ozone biases do not appear
to be due to an overly vigorous residual circulation, insufficient convection, or excessive
stratosphere/troposphere exchange, and so may be due to insufficient
vertical resolution or excessive vertical diffusion near the tropopause. In
the upper troposphere and lower stratosphere, model/measurement
intercomparisons are strongly affected by the averaging technique.
Compared to the pressure-averaged climatology, NH and
tropical mean model lower stratospheric biases are >20%. In the upper
troposphere, the 2°×2.5° simulation shows mean high biases of
~20% and ~35% during April in the tropics and NH
midlatitudes, respectively. This apparently good model/measurement agreement degrades when
relative-to-tropopause averages are considered, with upper troposphere high
biases of ~30% and 70% in the tropics and NH midlatitudes. This occurs
because relative-to-tropopause averaging better preserves the larger
cross-tropopause O3 gradients which are seen in the daily sonde data,
but not in daily model profiles. Relative-to-tropopause averages therefore
more accurately reveal model/measurement discrepancies.
The relative annual cycle of ozone near the
tropopause is reproduced very well in the model Northern Hemisphere
midlatitudes. In the tropics, the model amplitude of the near-tropopause
annual cycle is weak. This is likely due to the annual amplitude of mean
vertical upwelling near the tropopause, which analysis suggests is ~30% weaker than in the real atmosphere. |
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