Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 8 3 2008 10.5194/acp-8-697-2008 http://www.atmos-chem-phys.net/8/697/2008/ http://www.atmos-chem-phys.net/8/697/2008/acp-8-697-2008.html http://www.atmos-chem-phys.net/8/697/2008/acp-8-697-2008.pdf 697 707 2008-02-12 Turbulent vertical diffusivity in the sub-tropical stratosphere I. Pisso ipisso@lmd.ens.fr B. Legras Laboratoire de Météorologie Dynamique UMR 8539, Paris, France Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and paramaterized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Centre for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). 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