Interannual variability of stratospheric trace gases: The role of extratropical wave driving

The interannual variability of methane and ozone from a 35-year middle atmosphere climate model simulation with no interannual variations in external forcing or chemistry is examined. The internal dynamics in the model produces large tracer interannual variability, particularly in polar regions. During winter and spring the interannual standard deviation in the polar lower-middle stratosphere is about 30% of the climatological mean for methane and 15% for ozone. Global-scale, coherent interannual variations in temperature, residual circulation, and tracers are correlated with variability in the extratropical wave forcing. Statistically significant positive correlations between wave driving and polar tracer tendencies, including column ozone, occur from autumn to spring in both hemispheres. These positive correlations imply that interannual variations in polar tracers are dominated by variations in the horizontal eddy transport and not by variations in residual mean descent rates.