Atmos. Chem. Phys. Discuss., 9, 11551-11587, 2009
www.atmos-chem-phys-discuss.net/9/11551/2009/
doi:10.5194/acpd-9-11551-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
First multi-year occultation observations of CO2 in the MLT by ACE satellite: observations and analysis using the extended CMAM
S. R. Beagley1, C. D. Boone2, V. I. Fomichev1, J. J. Jin1, K. Semeniuk1, J. C. McConnell1, and P. F. Bernath2,3
1Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada
2Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada
3Department of Chemistry, University of York, Heslington, York, UK

Abstract. This paper presents the first multi-year 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 measurements (~70 km) but lower than in the SABER 1.06 (~82 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 analysing the disagreement, we have investigated the variation of several parameters of interest, photolysis rates, formation rate for CO2, and the impact of uncertainty in 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 vertical eddy diffusion in 3-D models in determining the distribution of candidate species in the mesosphere which requires further study.

Citation: Beagley, S. R., Boone, C. D., Fomichev, V. I., Jin, J. J., Semeniuk, K., McConnell, J. C., and Bernath, P. F.: First multi-year occultation observations of CO2 in the MLT by ACE satellite: observations and analysis using the extended CMAM, Atmos. Chem. Phys. Discuss., 9, 11551-11587, doi:10.5194/acpd-9-11551-2009, 2009.
 
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