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Published December 30, 2008 | Published
Journal Article Open

Simulation of upper tropospheric CO₂ from chemistry and transport models


The California Institute of Technology/Jet Propulsion Laboratory two-dimensional (2-D), three-dimensional (3-D) GEOS-Chem, and 3-D MOZART-2 chemistry and transport models (CTMs), driven respectively by NCEP2, GEOS-4, and NCEP1 reanalysis data, have been used to simulate upper tropospheric CO2 from 2000 to 2004. Model results of CO2 mixing ratios agree well with monthly mean aircraft observations at altitudes between 8 and 13 km (Matsueda et al., 2002) in the tropics. The upper tropospheric CO2 seasonal cycle phases are well captured by the CTMs. Model results have smaller seasonal cycle amplitudes in the Southern Hemisphere compared with those in the Northern Hemisphere, which are consistent with the aircraft data. Some discrepancies are evident between the model and aircraft data in the midlatitudes, where models tend to underestimate the amplitude of CO2 seasonal cycle. Comparison of the simulated vertical profiles of CO2 between the different models reveals that the convection in the 3-D models is likely too weak in boreal winter and spring. Model sensitivity studies suggest that convection mass flux is important for the correct simulation of upper tropospheric CO2.

Additional Information

© 2008 American Geophysical Union. Received 30 June 2007; accepted 21 August 2008; published 30 December 2008. This work is performed at JPL under contract with NASA and is supported by project 102438-01.01.01. We thank J. Randerson for useful inputs and helpful comments, two anonymous reviewers, and C.L. Quere for helpful comments. Our special thanks to Bob Yantosca at Harvard University for the help on the GEOS-Chem model and to Peter Hess, Larry Horowitz, and Jean-Francois Lamar on the MOZART-2 model. R.L. Shia and Y.L. Yung are supported by NSF grant ATM-9903790. M.C. Liang also would like to acknowledge the support from an NSC grant 96-2628-M-001-018 to Academia Sinica.

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