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| Titel |
First multi-year occultation observations of CO2 in the MLT by ACE satellite: observations and analysis using the extended CMAM |
| VerfasserIn |
S. R. Beagley, C. D. Boone, V. I. Fomichev, J. J. Jin, K. Semeniuk, J. C. McConnell, P. F. Bernath |
| 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. 3 ; Nr. 10, no. 3 (2010-02-03), S.1133-1153 |
| Datensatznummer |
250008034
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| Publikation (Nr.) |
 copernicus.org/acp-10-1133-2010.pdf |
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| Zusammenfassung |
| This paper presents the first global set of observations of CO2 in the
mesosphere and lower thermosphere (MLT) obtained by the ACE-FTS instrument
on SCISAT-I, a small Canadian satellite launched in 2003. The observations
use the solar occultation technique and document the fall-off in the mixing
ratio of CO2 in the MLT region. The beginning of the fall-off of the
CO2, or "knee" occurs at about 78 km and lies higher than in the
CRISTA-1 measurements (~70 km) but lower than in the SABER 1.06
(~80 km) and much lower than in rocket measurements. We also present the
measurements of CO obtained concurrently which provide important constraints
for analysis. We have compared the ACE measurements with simulations of the
CO2 and CO distributions in the vertically extended version of the
Canadian Middle Atmosphere Model (CMAM). Applying standard chemistry we find
that we cannot get agreement between the model and ACE CO2 observations
although the CO observations are adequately reproduced. There appears to be
about a 10 km offset compared to the observed ACE CO2, with the model
"knee" occurring too high. In analyzing the disagreement, we have investigated
the variation of several parameters of interest (photolysis rates, formation
rate for CO2, and the impact of uncertainty in turbulent eddy
diffusion) in order to explore parameter space for this problem. Our
conclusions are that there must be a loss process for CO2, about 2–4~times
faster than photolysis that will sequester the carbon in some form
other than CO and we have speculated on the role of meteoritic dust as a
possible candidate. In addition, from this study we have highlighted a
possible important role for unresolved vertical eddy diffusion in 3-D models
in determining the distribution of candidate species in the mesosphere which
requires further study. |
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