Atmos. Chem. Phys. Discuss., 10, 14737-14769, 2010
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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.
The importance of transport model uncertainties for the estimation of CO2 sources and sinks using satellite measurements
S. Houweling1,2, I. Aben1, F.-M. Breon3, F. Chevallier3, N. Deutscher4, R. Engelen5, C. Gerbig6, D. Griffith4, K. Hungershoefer3,7, R. Macatangay4, J. Marshall6, J. Notholt8, W. Peters9, and S. Serrar5
1Netherlands Institute for Space Research (SRON), Utrecht, The Netherlands
2Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, The Netherlands
3Laboratoire des Sciences du Climate et de l'Environnement, Gif sur Yvette, France
4Centre for Atmospheric Chemistry, University of Wollongong, Australia
5European Centre for Medium Range Weather Forecasts (ECMWF), Reading, UK
6Max Planck Institute for Biogeochemistry, Jena, Germany
7Deutscher Wetterdienst, Offenbach, Germany
8Institute of Environmental Physics, University of Bremen, Germany
9Dept. of Meteorology and Air Quality, Wageningen University, The Netherlands

Abstract. This study presents a synthetic model intercomparison to investigate the importance of transport model errors for estimating the sources and sinks of CO2 using satellite measurements. The experiments were designed for testing the potential performance of the proposed CO2 lidar A-SCOPE, but also apply to other space borne missions that monitor total column CO2. The participating transport models IFS, LMDZ, TM3, and TM5 were run in forward and inverse mode using common CO2 fluxes and initial concentrations. Simulated column averaged CO2 (xCO2) mixing ratios vary between the models by σ=0.5 ppm over the continents and σ=0.27 ppm over sea. A variable, but overall quite encouraging agreement is found in comparison with FTS measurements at Park Falls, Darwin, Spitsbergen, and Bremen. Despite the fact that the models agree on average on the sub-ppm level, these modest differences nevertheless lead to significant discrepancies in the inverted fluxes of 0.1 Pg C/yr per 106 km2 over land and 0.03 Pg C/yr per 106 km2 over the ocean. These transport model induced flux uncertainties exceed the target requirement that was formulated for the A-SCOPE mission of 0.02 Pg C/yr per 106 km2, and could also limit the overall performance of other CO2 missions such as GOSAT. It is concluded that to make use of the remote sensing technique for quantifying the sources and sinks of CO2 not only requires highly accurate satellite instruments, but also puts stringent requirements on the performance of atmospheric transport models. Further development of these models should receive high priority.

Citation: Houweling, S., Aben, I., Breon, F.-M., Chevallier, F., Deutscher, N., Engelen, R., Gerbig, C., Griffith, D., Hungershoefer, K., Macatangay, R., Marshall, J., Notholt, J., Peters, W., and Serrar, S.: The importance of transport model uncertainties for the estimation of CO2 sources and sinks using satellite measurements, Atmos. Chem. Phys. Discuss., 10, 14737-14769, doi:10.5194/acpd-10-14737-2010, 2010.
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