Geosci. Model Dev. Discuss., 5, 1561-1626, 2012
© Author(s) 2012. 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 Geoscientific Model Development (GMD). Please refer to the corresponding final paper in GMD.
The chemical transport model Oslo CTM3
O. A. Søvde1, M. J. Prather2, I. S. A. Isaksen1,3, T. K. Berntsen1,3, F. Stordal3, X. Zhu2, C. D. Holmes2, and J. Hsu2
1Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway
2Department of Earth System Science, University of California Irvine, California, USA
3Department of Geosciences, University of Oslo, Oslo, Norway

Abstract. We present here the global chemical transport model Oslo CTM3, an update of the Oslo CTM2. The update comprises a faster transport scheme, an improved wet scavenging scheme for large scale rain, updated photolysis rates and a new lightning parameterization. Oslo CTM3 is better parallelized and allows for stable, large time steps for advection, enabling more complex or high resolution simulations. Thorough comparisons between the Oslo CTM3, Oslo CTM2 and measurements are performed, and in general the Oslo CTM3 is found to reproduce measurements well. Inclusion of tropospheric sulfur chemistry and nitrate aerosols in CTM3 is shown to be important to reproduce tropospheric O3, OH and the CH4 lifetime well. Using the same meteorology to drive the two models, shows that some features related to transport are better resolved by the CTM3, such as polar cap transport, while features like transport close to the vortex edge are resolved better in the Oslo CTM2 due to its required shorter transport time step. The longer transport time steps in CTM3 result in larger errors e.g. near the jets, and when necessary, this can be remedied by using a shorter time step. An additional, more accurate and time consuming, treatment of polar cap transport is presented, however, both perform acceptably. A new treatment of the horizontal distribution of lightning is presented and found to compare well with measurements. Vertical distributions of lighting are updated, and tested against the old vertical distribution. The new profiles are found to produce more NOx in the tropical middle troposphere, and less at the surface and at high altitudes.

Citation: Søvde, O. A., Prather, M. J., Isaksen, I. S. A., Berntsen, T. K., Stordal, F., Zhu, X., Holmes, C. D., and Hsu, J.: The chemical transport model Oslo CTM3, Geosci. Model Dev. Discuss., 5, 1561-1626, doi:10.5194/gmdd-5-1561-2012, 2012.
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