Atmos. Chem. Phys. Discuss., 6, 4375-4414, 2006
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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.
Key aspects of stratospheric tracer modeling
B. Bregman, E. Meijer, and R. Scheele
Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE, De Bilt, The Netherlands

Abstract. This study describes key aspects of global chemistry-transport models and the impact on stratospheric tracer transport. We concentrate on global models that use assimilated winds from numerical weather predictions, but the results also apply to tracer transport in general circulation models. We examined grid resolution, numerical diffusion and dispersion of the winds fields, the meteorology update time intervals, update frequency, and time interpolation. For this study we applied the three-dimensional chemistry-transport Tracer Model version 5 (TM5) and a trajectory model and performed several diagnoses focusing on different transport regimes. Covering different time and spatial scales, we examined (1) polar vortex dynamics during the Arctic winter, (2) the large-scale stratospheric meridional circulation, and (3) air parcel dispersion in the tropical lower stratosphere. Tracer distributions inside the Arctic polar vortex show considerably worse agreement with observations when the model grid resolution in the polar region is reduced to avoid numerical instability. Using time interpolated winds improve the tracer distributions only marginally. Considerable improvement is found when the update frequency of the assimilated winds is increased from 6 to 3h, both in the large-scale tracer distribution and the polar regions. It further reduces in particular the vertical dispersion of air parcels in the tropical lower stratosphere. The results in this study demonstrates significant progress in the use of assimilated meteorology in chemistry-transport models, which is important for both short- and long-term integrations.

Citation: Bregman, B., Meijer, E., and Scheele, R.: Key aspects of stratospheric tracer modeling, Atmos. Chem. Phys. Discuss., 6, 4375-4414, doi:10.5194/acpd-6-4375-2006, 2006.
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