Atmos. Chem. Phys. Discuss., 10, 20355-20404, 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.
Tropical deep convection and its impact on composition in global and mesoscale models – Part 2: Tracer transport
C. R. Hoyle1,2, V. Marécal7, M. R. Russo9, J. Arteta6, C. Chemel4, M. P. Chipperfield3, F. D'Amato13, O. Dessens12, W. Feng3, N. R. P. Harris11, J. S. Hosking12,*, O. Morgenstern5,**, T. Peter1, J. A. Pyle9, T. Reddmann10, N. A. D. Richards3, P. J. Telford11, W. Tian3, S. Viciani, O. Wild8, X. Yang12, and G. Zeng5
1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
2Department of Geosciences, University of Oslo, Norway
3Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, UK
4NCAS-Weather, Centre for Atmospheric & Instrumentation Research, \newline University of Herfordshire, UK
5NCAS-Chemistry Climate, Department of Chemistry, Cambridge University, UK
6Centre National de Recherches Météorologiques/Groupe détude de l'Atmosphére Météorologique, Météo-France and CNRS, Toulouse, France
7Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, CNRS and University of Orléans, Orléans, France
8Lancaster Environment Centre, Lancaster University, UK
9NCAS climate, Centre for Atmospheric Science, Department of Chemistry, \newline University of Cambridge, UK
10Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
11European Ozone Research Coordinating Unit, University of Cambridge Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, UK
12Centre for Atmospheric Science, University of Cambridge, Cambridge, UK
13CNR-INO (Istituto Nazionale di Ottica) Largo E. Fermi, 6 50125 Firenze, Italy
*now at: British Antarctic Survey, Cambridge, UK
**now at: the National Institute of Water and Atmospheric Research, Lauder, New Zealand

Abstract. The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemistry transport, and climate chemistry models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short lived tracers (with a lifetime of 6 hours) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to differ between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for the modelling of the halogen burden of the lowermost stratosphere through species such as bromoform, or for the transport of short lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are found to be strongly influenced by the convective transport parameterisations, and boundary layer mixing parameterisations of the models. The location of rapid transport into the upper troposphere is similar among the models, and is mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, none of the models indicates significant enhancement in upward transport over western Africa. The mean mixing ratios of an idealised CO like tracer in the upper tropical troposphere are found to be sensitive to the surface CO mixing ratios in the regions with the most active convection, revealing the importance of correctly modelling both the location of convective transport and the geographical pollutant emission patterns.

Citation: Hoyle, C. R., Marécal, V., Russo, M. R., Arteta, J., Chemel, C., Chipperfield, M. P., D'Amato, F., Dessens, O., Feng, W., Harris, N. R. P., Hosking, J. S., Morgenstern, O., Peter, T., Pyle, J. A., Reddmann, T., Richards, N. A. D., Telford, P. J., Tian, W., Viciani, S., Wild, O., Yang, X., and Zeng, G.: Tropical deep convection and its impact on composition in global and mesoscale models – Part 2: Tracer transport, Atmos. Chem. Phys. Discuss., 10, 20355-20404, doi:10.5194/acpd-10-20355-2010, 2010.
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