Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 7 9 2007 10.5194/acp-7-2435-2007 http://www.atmos-chem-phys.net/7/2435/2007/ http://www.atmos-chem-phys.net/7/2435/2007/acp-7-2435-2007.html http://www.atmos-chem-phys.net/7/2435/2007/acp-7-2435-2007.pdf 2435 2445 2007-05-11 Observationally derived transport diagnostics for the lowermost stratosphere and their application to the GMI chemistry and transport model S. E. Strahan sstrahan@pop600.gsfc.nasa.gov B. N. Duncan P. Hoor Goddard Earth Science and Technology Center, University of Maryland, Baltimore County, Baltimore, MD 21250, USA Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany Transport from the surface to the lowermost stratosphere (LMS) can occur on timescales of a few months or less, making it possible for short-lived tropospheric pollutants to influence stratospheric composition and chemistry. Models used to study this influence must demonstrate the credibility of their chemistry and transport in the upper troposphere and lower stratosphere (UT/LS). Data sets from satellite and aircraft instruments measuring CO, O₃, N₂O, and CO₂ in the UT/LS are used to create a suite of diagnostics for the seasonally-varying transport into and within the lowermost stratosphere, and of the coupling between the troposphere and stratosphere in the extratropics. The diagnostics are used to evaluate a version of the Global Modeling Initiative (GMI) Chemistry and Transport Model (CTM) that uses a combined tropospheric and stratospheric chemical mechanism and meteorological fields from the GEOS-4 general circulation model. The diagnostics derived from N₂O and O₃ show that the model lowermost stratosphere has realistic input from the overlying high latitude stratosphere in all seasons. Diagnostics for the LMS show two distinct layers. 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