Atmos. Chem. Phys. Discuss., 5, 10217-10258, 2005
www.atmos-chem-phys-discuss.net/5/10217/2005/
doi:10.5194/acpd-5-10217-2005
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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.
Implementation issues in chemistry and transport models
S. E. Strahan1 and B. C. Polansky2
1University of Maryland, Baltimore County Goddard Earth Science and Technology Center, 5523 Research Park Dr., Suite 320, Baltimore, MD, 21 228, USA
2Science Systems and Applications, Inc., 10210 Greenbelt Rd., Suite 600, Lanham, MD, 20 706, USA

Abstract. Offline chemistry and transport models (CTMs) are versatile tools for studying composition and climate issues requiring multi-decadal simulations. They are computationally fast compared to coupled chemistry climate models, making them well-suited for integrating sensitivity experiments necessary for understanding model performance and interpreting results. The archived meteorological fields used by CTMs can be implemented with lower horizontal or vertical resolution than the original meteorological fields in order to shorten integration time, but the effects of these shortcuts on transport processes must be understood if the CTM is to have credibility. In this paper we present a series of CTM experiments, each differing from another by a single feature of the implementation. Transport effects arising from changes in resolution and model lid height are evaluated using process-oriented diagnostics that intercompare CH4, O3, and age tracer carried in the simulations. Some of the diagnostics used are derived from observations and are shown as a reality check for the model. Processes evaluated include the tropical ascent, tropical-midlatitude exchange, the poleward circulation in the upper stratosphere, and the development of the Antarctic vortex. We find that faithful representation of stratospheric transport in this CTM using Lin and Rood advection is possible with a full mesosphere, ~1 km resolution in the lower stratosphere, and relatively low vertical resolution (>4 km spacing) in the middle stratosphere and above, but lowering the lid from the upper to lower mesosphere leads to less realistic constituent distributions in the upper stratosphere. Ultimately, this affects the polar lower stratosphere, but the effects are greater for the Antarctic than the Arctic. The fidelity of lower stratospheric transport requires realistic tropical and high latitude mixing barriers which are produced at 2°×2.5°, but not lower resolution. At 2°×2.5° resolution, the CTM produces a vortex capable of isolating perturbed chemistry (e.g. high Cly and low NOy) required for simulating polar ozone loss.

Citation: Strahan, S. E. and Polansky, B. C.: Implementation issues in chemistry and transport models, Atmos. Chem. Phys. Discuss., 5, 10217-10258, doi:10.5194/acpd-5-10217-2005, 2005.
 
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