Residual mean transport in the stratosphere: Contributions from wave driving and seasonal transience

A three-dimensional model of dynamics and photochemistry is used to evaluate the contributions to residual mean motion and ozone transport from planetary wave drag, gravity wave drag and from the seasonal transience of diabatic cooling. The integrations reveal that over much of the winter hemisphere, seasonal transience plays a major role in driving residual mean motion. During autumn, when the seasonal drift of radiative equilibrium temperature is fast, that contribution dominates. Following solstice, the dominant contribution to residual mean motion swings to wave driving. Similar dependence is reflected in the wintertime increase of total ozone and in the transfer of stratospheric ozone to the troposphere. Owing to the substantial contribution from seasonal transience, only about half of the net wintertime increase of Northern Hemisphere ozone (spring-autumn) is actually available to change through changes of wave driving. Observed changes then represent nearly all of the wintertime increase that is available to change.