Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 2 2006 10.5194/acpd-6-3403-2006 http://www.atmos-chem-phys-discuss.net/6/3403/2006/ http://www.atmos-chem-phys-discuss.net/6/3403/2006/acpd-6-3403-2006.html http://www.atmos-chem-phys-discuss.net/6/3403/2006/acpd-6-3403-2006.pdf 3403 3417 2006-04-28 Persistence and photochemical decay of springtime total ozone anomalies in the Canadian Middle Atmosphere Model S. Tegtmeier T. G. Shepherd Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany Department of Physics, University of Toronto, Toronto, Ontario, Canada The persistence and decay of springtime total ozone anomalies over the entire extratropics (midlatitudes plus polar regions) is analysed using results from the Canadian Middle Atmosphere Model (CMAM), a comprehensive chemistry-climate model. As in the observations, interannual anomalies established through winter and spring persist with very high correlation coefficients (above 0.8) through summer until early autumn, while decaying in amplitude as a result of photochemical relaxation in the quiescent summertime stratosphere. The persistence and decay of the ozone anomalies in CMAM agrees extremely well with observations, even in the southern hemisphere when the model is run without heterogeneous chemistry (in which case there is no ozone hole and the seasonal cycle of ozone is quite different from observations), and even in the northern hemisphere where this version of CMAM (run with fixed external forcing) strongly underestimates the observed interannual variability. This shows that ozone anomaly persistence and decay does not depend on how the springtime anomalies are created or on their magnitude, but reflects the transport and photochemical decay in the model. It is thus a robust diagnostic of model performance.