The Influence of Ozone Changes on the Stratospheric Dynamics in 4xCO2 Climate Simulations

Abstract

An increase in atmospheric CO2 concentration changes the temperatures and dynamics of the stratosphere and thus also the ozone concentrations. Since ozone is sensitive to longwave as well as shortwave radiation, the altered ozone distribution in turn affects temperature and thus also modifies the CO2-induced change in stratospheric dynamics. To study this in detail, we performed model simulations using the EMAC climate-chemistry model in which CO2 concentrations were quadrupled compared to pre-industrial times. For the 4xCO2 simulations, this was done by prescribing once an unchanged (pre-industrial) and once a changed ozone distribution from a previous 4xCO2 simulation. It is shown here, that the change in ozone leads to a strengthening of the stratospheric easterly winds in summer, as well as a weakening of the polar vortex in both hemispheres. While the high variability in the northern hemisphere does not lead to clear results, they are statistically significant in the southern hemisphere. In addition, the duration of the polar vortex westerlies is shorter due to the CO2-induced change in the ozone field. Furthermore, the acceleration of the Brewer-Dobson circulation, which is caused by an increase in CO2, is damped in the summer hemisphere by the ozone influence. This in turn affects the transport from the tropics to the extra-tropics. The ozone-induced changes in the stratospheric circulation also affect the tropospheric circulation and have an effect on the tropospheric polar front jet. It experiences a systematically weaker shift toward the pole due to a changed ozone distribution in the southern hemisphere than with a constant ozone distribution. We discuss the results, presented here, and place them in the context of the influence of stratospheric ozone on climate change dynamics.