Sensitivity of polar ozone to sea surface temperatures and halogen amounts

Coupled chemistry-climate model simulations are presented for the period 1951-2099 and 1951-2007. The model includes a tested parameterization for the production of active halogens from the source molecules. In run 1 the observed levels of chlorine and bromine are specified, as well as the sea surface temperatures (SSTs) from a coupled ocean-atmosphere model. Run 2 is identical to run 1 but observed SSTs are specified instead of model SSTs. In run 3 the bromine amount is reduced by 25% but otherwise the simulation is identical to run 2. The results show that the ozone hole is sensitive to SSTs and bromine amounts. For the period 1990-2007, when the ozone hole was fully developed, the area of the ozone hole was simulated to be largest in run 1 (11% smaller than observed), compared with underpredictions of 17% and 27% for runs 2 and 3, respectively. The effect of SSTs (difference between runs 1 and 2) is shown to arise from changes in the strength of the Brewer-Dobson circulation, which is weaker for the simulation with model SSTs. The sensitivity of the model results to bromine (difference between runs 2 and 3) indicates the need to include realistic bromine amounts as well as chlorine and may explain, in part, the substantial underpredictions of the ozone hole area in previous simulations. The results also suggest that a small residual ozone hole may still be present after 2070 and that the ozone hole may not disappear entirely this century.