TRENDS IN LOWER STRATOSPHERIC ZONAL WINDS, ROSSBY WAVE BREAKING BEHAVIOR, AND COLUMN OZONE AT NORTHERN MID-LATITUDES

Regression relationships between 330 K potential vorticity and total ozone deviations derived from monthly mean measurements on the northern hemisphere have been applied to estimate that as much as 40% of the zonal mean column ozone decline at mid-latitudes in February during the 1979 to 1999 period may be attributed to long-term trends in eddy transport across the subtropical tropopause. Specifically, Rossby wave breaking events transport ozone-poor air from the tropical upper troposphere into the mid-latitude, lowermost stratosphere. Trends in the meridional zonal wind field have tended to favor an increased occurrence rate of these breaking events during the 1990's as compared to the 1980's. As much as 25% of the mid-latitude ozone trend in March may also be attributed to trends in eddy transport. At specific longitudes, the contribution to ozone trends from this source (as well as long-term changes in quasi-stationary wave amplitudes and phases) can be well over 50%.