Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 4 9/10 2004 10.5194/acp-4-2313-2004 http://www.atmos-chem-phys.net/4/2313/2004/ http://www.atmos-chem-phys.net/4/2313/2004/acp-4-2313-2004.html http://www.atmos-chem-phys.net/4/2313/2004/acp-4-2313-2004.pdf 2313 2336 2004-11-26 Evaluation of archived and off-line diagnosed vertical diffusion coefficients from ERA-40 with ²²²Rn simulations D. J. L. Olivié P. F. J. van Velthoven A. C. M. Beljaars Royal Netherlands Meteorological Institute, De Bilt, The Netherlands Eindhoven University of Technology, Eindhoven, The Netherlands European Centre for Medium-range Weather Forecasts, Reading, UK Boundary layer turbulence has a profound influence on the distribution of tracers with sources or sinks at the surface. The 40-year ERA-40 meteorological data set of the European Centre for Medium-range Weather Forecasts contains archived vertical diffusion coefficients. We evaluated the use of these archived diffusion coefficients versus off-line diagnosed coefficients based on other meteorological parameters archived during ERA-40 by examining the influence on the distribution of the radionuclide ²²²Rn in the chemistry transport model TM3. In total four different sets of vertical diffusion coefficients are compared: (i) 3-hourly vertical diffusion coefficients archived during the ERA-40 project, (ii) 3-hourly off-line diagnosed coefficients from a non-local scheme based on Holtslag and Boville (1993), Vogelezang and Holtslag (1996), and Beljaars and Viterbo (1999), (iii) 6-hourly coefficients archived during the ERA-40 project, and (iv) 6-hourly off-line diagnosed coefficients based on a local scheme described in Louis (1979) and Louis et al. (1982). The diffusion scheme to diagnose the coefficients off-line in (ii) is similar to the diffusion scheme used during the ERA-40 project (i and iii).