Structure and long-term change in the zonal asymmetry in Antarctic total ozone during spring

The quasi-stationary asymmetry of total ozone over Antarctica during spring is studied by TOMS data during the period 1979-2005. Statistics on the amplitude and longitudinal position of zonal anomalies are obtained from the distribution of total ozone along seven individual latitudes at 5-degree intervals between 50 degrees S and 80 degrees S. As shown by the September-November means, the mid-latitude collar of ozone-rich stratospheric air has a sub-Antarctic maximum with a mean location in the quadrant 90 degrees E-180 degrees E and a total ozone level of about 380 DU between 50 degrees S and 60 degrees S. The steady displacement and elongation of the ozone hole under the influence of planetary waves causes a zonal anomaly of low ozone in the sector 0 degrees-60 degrees W with total ozone levels of about 200 DU between 70 degrees S and 80 degrees S. Climatologically, the highest amplitude of the zonal anomaly is 57.2 +/- 13.5 DU (relative asymmetry of 32% between high and low ozone levels) at 65 degrees S latitude. A significant eastward shift of approximately 45 degrees in longitude is observed in the total ozone minimum over the Weddell Sea - South Atlantic sector during 1979-2005, whereas the zonal maximum is relatively stable in location. Also apparent is a long-term shift in tropopause temperature distribution in the region. The geographical distribution of the zonal extremes in total ozone for the seven latitudes shows that (i) the extremes exhibit sensitivity to the shape of the Antarctic continent, (ii) the stationarity of the extremes increases poleward above the edge of continent and (iii) the positions of the extremes at the higher latitudes tend to follow the meridionally oriented elements of orography. It is suggested that the radiative influence of Antarctica contributes to the formation of this pattern. Anomalies in the horizontal structure of the tropopause, which appear related to orography, support this view. Mechanisms involved in the formation and decadal change in the total ozone asymmetry, as well as possible influences of the asymmetry on the stratospheric thermal regimes and regional UV irradiance redistribution are discussed.