Aspects of stratospheric long-term changes induced by ozone depletion

The effect of the stratospheric ozone depletion on the thermal and dynamical structure of the middle atmosphere is assessed using two 5-member ensembles of transient GCM simulations; one including linear trends in ozone, the other not, for the 1980-1999 period. Simulated temperatures and observations are in good agreement in terms of mean values, autocorrelations and cross correlations. Annual-mean and seasonal temperature trends have been calculated using the same statistical analysis. Simulations show that ozone trends are responsible for reduced wave activity in the Arctic lower stratosphere in February and March, confirming both the role of dynamics in controlling March temperatures and a recently proposed mechanism whereby Arctic ozone depletion causes the reduction in wave activity entering the lower stratosphere. Changes in wave activity are consistent with an intensification of the polar vortex at the time of ozone depletion and with a weakened Brewer-Dobson circulation: A decrease of the dynamical warming/cooling associated with the descending/ascending branch of the wintertime mean residual circulation at high/low latitudes has been obtained through the analysis of temperature observations (1980-1999). Ozone is responsible of about one third of the decrease of this dynamical cooling at high latitudes. An increase in the residual mean circulation is seen in the observations for the 1965-1980 period.