Results of an interactively coupled atmospheric chemistry – general circulation model: Comparison with observations

摘要

The coupledclimate-chemistry model ECHAM4.L39(DLR)/CHEM is presented which enables asimultaneous treatment of meteorology and atmospheric chemistry and theirfeedbacks. This is the first model which interactively combines a generalcirculation model with a chemical model, employing most of the importantreactions and species necessary to describe the stratospheric and uppertropospheric ozone chemistry, and which is computationally fast enough to allowlong-term integrations with currently available computer resources. This ispossible as the model time-step used for the chemistry can be chosen as large asthe integration time-step for the dynamics. Vertically the atmosphere isdiscretized by 39 levels from the surface up to the top layer which is centred at 10 hPa, with a relatively high vertical resolution of approximately 700 mnear the extra-tropical tropopause. We present the results of a controlsimulation representing recent conditions (1990) and compare it to availableobservations. The focus is on investigations of stratospheric dynamics andchemistry relevant to describe the stratospheric ozone layer. ECHAM4.L39(DLR)/CHEMreproduces main features of stratospheric dynamics in the arctic vortex region,including stratospheric warming events. This constitutes a major improvementcompared to earlier model versions. However, apparent shortcomings in Antarctic circulation and temperatures persist. The seasonal and interannual variabilityof the ozone layer is simulated in accordance with observations. Activation anddeactivation of chlorine in the polar stratospheric vortices and theirinter-hemispheric differences are reproduced. Considering methane oxidation aspart of the dynamic-chemistry feedback results in an improved representation ofthe spatial distribution of stratospheric water vapour concentrations. Thecurrent model constitutes a powerful tool to investigate, for instance, thecombined direct and indirect effects of anthropogenic trace gas emissions.Key words. Atmospheric compositionand structure (middle atmosphere – composition and chemistry) – Meteorologyand atmospheric dynamics (general circulation; middle atmosphere dynamics)