Contribution of stratospheric ozone to the interannual variability of tropospheric ozone in the northern extratropics

We examined the role of variability in the input of stratospheric ozone on the interannual variability of tropospheric ozone in the northern extratropics using correlations of monthly ozone anomalies for the lower stratosphere and the troposphere. We used output from a multiyear simulation of the NASA Goddard Space Flight Center (GSFC) Chemistry and Transport Model (CTM), and evaluated model results using ozonesonde data. The GSFC CTM explicitly calculates stratospheric ozone and simulates separate tracers of stratospheric and tropospheric ozone (O-3-strat and O-3-trop, respectively). The climatological seasonal cycle of ozone shows that O-3-strat contributes significantly to the spring maximum of ozone at 500 hPa, similar to 40% at high latitudes and similar to 30% at midlatitudes. We find large regional differences in the correlation of ozone in the lower stratosphere and troposphere in the model that are supported by the ozonesonde data. Highest correlations are found from the eastern Atlantic to Europe, from the eastern Pacific to the western United States, and over the polar regions, in winter-spring. This spatial pattern is due to the input of O-3-strat into the troposphere. The distribution and time lag of the correlations (highest with no lag for midlatitudes and a 1-2 month lag for polar regions) are consistent with the dynamical indicators of stratosphere-troposphere exchange (STE), such as storm tracks in the midlatitudes and slow descending motion in the polar region. Our simple approach can be widely applied to diagnose the effect of STE on tropospheric ozone.