ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-3-1833-2003 The impact of model grid zooming on tracer transport in the 1999/2000 Arctic polar vortex van den Broek M. M. P. 1 van Aalst M. K. 2 Bregman A. 3 Krol M. 2 Lelieveld J. 4 Toon G. C. 5 Garcelon S. 6 Hansford G. M. 6 Jones R. L. 6 Gardiner T. D. 7 Space Research Organization of the Netherlands (SRON), Utrecht, The Netherlands Institute for Marine and Atmospheric Research (IMAU), Utrecht, The Netherlands Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands Max-Planck-Institut für Chemie (MPI), Mainz, Germany Jet Propulsion Laboratory (JPL), Pasadena, USA Cambridge University, Cambridge, UK National Physical Laboratory (NPL), Teddington, UK 31 10 2003 3 5 1833 1847 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/3/1833/2003/acp-3-1833-2003.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/3/1833/2003/acp-3-1833-2003.pdf

We have used a 3D chemistry transport model to evaluate the transport of HF and CH<sub>4</sub> in the stratosphere during the Arctic winter of 1999/2000. Several model experiments were carried out with the use of a zoom algorithm to investigate the effect of different horizontal resolutions. Balloon-borne and satellite-borne observations of HF and CH<sub>4</sub> were used to test the model. In addition, air mass descent rates within the polar vortex were calculated and compared to observations.<br> <br> Outside the vortex the model results agree well with the observations, but inside the vortex the model underestimates the observed vertical gradient in HF and CH<sub>4</sub>, even when the highest available resolution (1º x 1º) is applied. The calculated diabatic descent rates agree with observations above potential temperature levels of 450 K. These model results suggest that too strong mixing through the vortex edge could be a plausible cause for the model discrepancies, associated with the calculated mass fluxes, although other reasons are also discussed.<br> <br> Based on our model experiments we conclude that a global 6º x 9º resolution is too coarse to represent the polar vortex, whereas the higher resolutions, 3º x 2º and 1º x 1º, yield similar results, even with a 6º x 9º resolution in the tropical region.