Lower stratospheric stationary waves and the longitude dependence of ozone trends in winter

At northern midlatitudes, total ozone trends are largest in winter when the longitudinal distribution of ozone is highly asymmetric owing to dynamical forcing by stationary, planetary-scale waves. A distinct longitude dependence of these midlatitude trends for the 1979 to 1991 time period has previously been derived statistically from Nimbus 7 total ozone mapping spectrometer data. Here we apply a mechanistic ozone transport model to investigate the extent to which the geographic dependence of total ozone trends in January can be explained as being due to decadal changes in the amplitudes and phases of stationary planetary waves. Results indicate that most or all of the statistically derived geographic dependence can be explained in this manner. In support of the mechanistic model calculations, lower stratospheric geopotential height differences or ''anomalies'' between groups of Januaries near the end of the 1980s and near the beginning of the 1980s are inversely correlated with the geographic distribution of ozone trends. The observed decadal changes in upper tropospheric and lower stratospheric stationary wave properties are most probably a consequence of decadal climate variability in the troposphere.