Transport of ozone-depleted air on the breakup of the stratospheric polar vortex in spring/summer 2000

A high‐resolution three‐dimensional off‐line chemical transport simulation has been performed with the SLIMCAT model to examine transport and mixing of ozone depleted air in the lower stratosphere on breakup of the polar vortex in spring/summer 2000. The model included ozone, N2O, and F11 tracers and used simplified chemistry parameterizations. The model was forced by T106 European Centre for Medium‐Range Weather Forecasts analyses. The model results show that, by the end of June, above 420 K, much of the ozone‐depleted air is transported from polar regions to the subtropics. In contrast, below 420 K, most of the ozone‐depleted air remains poleward of approximately 55°N. It is suggested that the influence of the upper extension of the tropospheric subtropical jet provides a transport barrier at lower levels, while strong stirring on breakup of the polar vortex is important at upper levels. The mean meridional circulation modifies the distribution of ozone‐depleted air by moving it up the subtropics and down in the extratropics. The model simulation is validated by comparing vertical profiles of ozone loss against ozonesonde measurements. The model results are consistent with many of the features present in the ozonesonde measurements. F11‐N2O correlation plots are examined in the model and they show distinct canonical correlation curves for the polar vortex, midlatitudes, and the tropics. Comparison against balloon and aircraft measurements show that the model reproduces the separation between the vortex and midlatitude curves; however, the ratio of N2O to F11 lifetimes is somewhat too small in the model. It is shown that anomalies from the midlatitude canonical correlation curve can be used to identify remnants of polar vortex air which has mixed with midlatitude air. At the end of June there is excellent agreement in the position of air with anomalous F11‐N2O tracer correlation and ozone‐depleted air from the polar vortex.