Coupling of Arctic ozone and stratospheric dynamics and its influence on surface climate: the role of CFC concentrations.

Arctic stratospheric ozone has been shown to exert a statistically significant influence on Northern Hemispheric surface climate. This suggests that Arctic ozone is not only passively responding to dynamical variability in the stratosphere, but actively feeds back into the circulation through chemical and radiative processes. However, the extent and causality of the chemistry-dynamics coupling is still unknown. Since many state-of-the-art climate models lack a sufficient representation of ozone-dynamic feedbacks, a quantification of this coupling can be used to improve intra-seasonal weather and long-term climate forecasts.

We assess the importance of the ozone-dynamics coupling by performing simulations with and without interactive chemistry in two Chemistry Climate Models. The chemistry-dynamics coupling was examined in two different sets of time-slice simulations: one using pre-industrial, and one using year-2000 boundary conditions. We focus on the impact of sudden stratospheric warmings (SSW) and strong vortex events on stratosphere-troposphere coupling, since these go along with strong ozone anomalies and therefore an intensified ozone feedback.  We compare the runs with and without interactive chemistry.

For pre-industrial conditions, simulations without interactive ozone show a more intense and longer lasting surface signature of SSWs compared to simulations with interactive chemistry. Conversely, for year-2000 conditions, the opposite effect is found: interactive chemistry amplifies the surface signature of SSWs. Following these results, atmospheric CFC concentrations, which differ greatly in the pre-industrial and year-2000 runs, determine the sign of the ozone-circulation feedback, and thus have a strong impact on chemistry-climate coupling. Implications for modeling of stratosphere-troposphere coupling and future projections are discussed.