Sensitivity of dynamics and ozone to different representations of SSTs in the Unified Model

We use a version of the Met Office Unified Model with a simple stratospheric chemistry to perform a set of multi-annual integrations of 20 years each. The runs have different representations of ozone in the radiation and use prescribed sea surface temperatures (SSTs). In one experiment the same long-term mean monthly mean SSTs are used each model year, whereas all other experiments use annual varying AMIP II monthly mean SSTs instead. All runs have the same simplified ozone chemistry included (regardless of which ozone is used in the radiation), so we can estimate the impact of dynamical changes on ozone. We contrast the sensitivity of the model system towards the representation of ozone with the changes associated with the removal of the interannual variability in SSTs. We show that the appearance of extreme events in the northern hemisphere winter stratosphere as modelled with the Unified Model is linked more to the representation of SSTs than it is to ozone.