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| Titel |
Analysis of CO in the tropical troposphere using Aura satellite data and the GEOS-Chem model: insights into transport characteristics of the GEOS meteorological products |
| VerfasserIn |
Junhua Liu, J. A. Logan, D. B. A. Jones, N. J. Livesey, I. Megretskaia, C. Carouge, P. Nédélec |
| 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 ; 10, no. 24 ; Nr. 10, no. 24 (2010-12-23), S.12207-12232 |
| Datensatznummer |
250008976
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| Publikation (Nr.) |
 copernicus.org/acp-10-12207-2010.pdf |
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| Zusammenfassung |
| We use the GEOS-Chem chemistry-transport model (CTM) to interpret the
spatial and temporal variations of tropical tropospheric CO observed by the
Microwave Limb Sounder (MLS) and the Tropospheric Emission Spectrometer
(TES). In so doing, we diagnose and evaluate transport in the GEOS-4 and
GEOS-5 assimilated meteorological fields that drive the model, with a
particular focus on vertical mixing at the end of the dry season when
convection moves over the source regions. The results indicate that over
South America, deep convection in both GEOS-4 and GEOS-5 decays at too low
an altitude early in the wet season, and the source of CO from isoprene in
the model (MEGAN v2.1) is too large, causing a lag in the model's seasonal
maximum of CO compared to MLS CO in the upper troposphere (UT). TES and MLS
data reveal problems with excessive transport of CO to the eastern
equatorial Pacific and lofting in the ITCZ in August and September,
particularly in GEOS-4. Over southern Africa, GEOS-4 and GEOS-5 simulations
match the phase of the observed CO variation from the lower troposphere (LT)
to the UT fairly well, although the magnitude of the seasonal maximum is
underestimated considerably due to low emissions in the model. A sensitivity
run with increased emissions leads to improved agreement with observed CO in
the LT and middle troposphere (MT), but the amplitude of the seasonal
variation is too high in the UT in GEOS-4. Difficulty in matching CO in the
LT and UT implies there may be overly vigorous vertical mixing in GEOS-4
early in the wet season. Both simulations and observations show a time lag
between the peak in fire emissions (July and August) and in CO (September
and October). We argue that it is caused by the prevailing subsidence in the
LT until convection moves south in September, as well as the low sensitivity
of TES data in the LT over the African Plateau. The MLS data suggest that
too much CO has been transported from fires in northern Africa to the UT in
the model during the burning season, as does MOZAIC aircraft data, perhaps
as a result of the combined influence of too strong Harmattan winds in the
LT and too strong vertical mixing over the Gulf of Guinea in the model. |
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