Ozone climatology using interactive chemistry: Results from the Canadian Middle Atmosphere Model

The climatology of ozone produced by the Canadian Middle Atmosphere Model ( CMAM) is presented. This three-dimensional global model incorporates the ra diative feedbacks of ozone and water vapor calculated on-line with a photoc hemical module. This module includes a comprehensive gas-phase reaction set and a limited set of heterogeneous reactions to account for processes occu rring on background sulphate aerosols. While transport is global, photochem istry is solved from about 400 hPa to the top of the model at similar to 95 km. This approach provides a complete and comprehensive representation of transport, emission, and photochemistry of various constituents from the su rface to the mesopause region. A comparison of model results with observati ons indicates that the ozone distribution and variability are in agreement with observations throughout most of the model domain. Column ozone annual variation is represented to within 5-10% of the observations except in the Southern Hemisphere for springtime high latitudes. The vertical ozone distr ibution is generally well represented by the model up to the mesopause regi on. Nevertheless, in the upper stratosphere, the model generally underestim ates the amount of ozone as well as the latitudinal tilting of ozone isople ths at high latitude. Ozone variability is analyzed and compared with measu rements. The comparison shows that the phase and amplitude of the seasonal variation as well as shorter timescale variations are well represented by t he model at various latitudes and heights. Finally, the impact of incorpora ting ozone radiative feedback on the model climatology is isolated. It is f ound that the incorporation of ozone radiative feedback results in a coolin g of similar to8 K in the summer stratopause region, which corrects a warm bias that results when climatological ozone is used.