Variability of total ozone due to the NAO as represented in two different model systems

To explain regional trends and long time variability of ozone the understanding and quantification of dynamical mechanisms influencing the zonal asymmetry of ozone is essential. Therefore we assess here the relationship between total ozone variability and the North Atlantic Oscillation (NAO), one of the dominant modes of variability in the European sector using two different model systems in conjunction with the same simplified ozone chemistry. One model is the Met Office Unified Model, which is a comprehensive general circulation model forced by prescribed sea-surface temperatures only. The other model is the chemistry-transport model SLIMCAT, which is driven by meteorological observations and therefore includes observed meteorological trends. The simplified ozone chemistry is based on the Cariolle scheme with an additional parameterization of polar ozone loss, but with no allowance for changing chlorine or aerosol levels. It is shown that the NAO signal in ozone during mid-winter is well represented in both model systems. Geopotential height correlations are used to explain the spatial pattern. It is demonstrated that composites of total ozone derived from the model integrations are capable of capturing the observed spatial characteristics as seen in TOMS data. Implications are drawn for NAO induced long time variability/regional trends of ozone.