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| Titel |
Diagnosing the transition layer at extratropical latitudes using MLS O3 and MOPITT CO analyses |
| VerfasserIn |
J. Barré, L. Amraoui, P. Ricaud, W. A. Lahoz, J.-L. Attié, V.-H. Peuch, B. Josse, V. Marecal |
| 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 ; 13, no. 14 ; Nr. 13, no. 14 (2013-07-30), S.7225-7240 |
| Datensatznummer |
250018789
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| Publikation (Nr.) |
 copernicus.org/acp-13-7225-2013.pdf |
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| Zusammenfassung |
| The behavior of the extratropical transition layer (ExTL) is investigated
using a chemistry transport model (CTM) and analyses derived from
assimilation of MLS (Microwave Limb Sounder) O3 and MOPITT (Measurements
Of Pollution In The Troposphere) CO data. We firstly focus on a
stratosphere–troposphere exchange (STE) case study that occurred on 15
August 2007 over the British Isles (50° N, 10° W). We
evaluate the effect of data assimilation on the O3–CO correlations. It is
shown that data assimilation disrupts the relationship in the transition
region. When MLS O3 is assimilated, CO and O3 values are not consistent
between each other, leading to unphysical correlations at the STE location.
When MLS O3 and MOPITT CO assimilated fields are taken into account in the
diagnostics the relationship happens to be more physical. We then use
O3–CO correlations to quantify the effect of data assimilation on the
height and depth of the ExTL. When the free-model run O3 and CO fields are
used in the diagnostics, the ExTL distribution is found 1.1 km above the
thermal tropopause and is 2.6 km wide (2σ). MOPITT CO analyses only
slightly sharpen (by −0.02 km) and lower (by −0.2 km) the ExTL
distribution. MLS O3 analyses provide an expansion (by +0.9 km) of the
ExTL distribution, suggesting a more intense O3 mixing. However, the MLS
O3 analyses ExTL distribution shows a maximum close to the thermal
tropopause and a mean location closer to the thermal tropopause
(+0.45 km). When MLS O3 and MOPITT CO analyses are used together, the
ExTL shows a mean location that is the closest to the thermal tropopause
(+0.16 km). We also extend the study at the global scale on 15 August 2007
and for the month of August 2007. MOPITT CO analyses still show a narrower
chemical transition between stratosphere and troposphere than the free-model
run. MLS O3 analyses move the ExTL toward the troposphere and broaden it.
When MLS O3 analyses and MOPITT CO analyses are used together, the ExTL
matches the thermal tropopause poleward of 50°. |
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