Seasonal Differences in the Trend of Total Ozone and Contributions from Tropospheric and Stratospheric Layers

Based on an average of the total-ozone changes determined by means of linear regression at individual Dobson stations within climatic zones, trends of total ozone for each of the four seasons have been evaluated for five climatic zones, and the world; intervals are 1960–84, 1965–84, 1970–84 and 1975–84. Based on ozonesonde data, trends of ozone by season in 2–8 km, 8–16 km, 16–24 km and 24–32 km layers have been evaluated for the four extratropical climatic zones for intervals 1965–84, 1970–84 and 1975–84. The decrease in September–October–November (SON) total ozone relative to other seasons in the south polar zone (Antarctica) is observed in the last 10–15 years also in south temperate, tropical and north polar zones, and for the world as a whole, but the seasonal differences in trend are significant only in the south polar zone. In the north temperate zone, where the data are most numerous, the total ozone has decreased in December-January-February (DJF) relative to other seasons, although in the last decade the trends in DJF and SON an comparable. The decrease in SON total ozone relative to other seasons is indicated to be due mainly to an ozone decrease in the 16-24 km layer of the south polar zone and the 24-32 km layer of south temperate and north polar zones, but once again the seasonal differences in trend are not significant. There are inconsistencies in the north temperate zone between relative seasonal changes in total ozone and layer-mean ozone, casting doubt on the representativeness of the ozonesonde data. There has been a substantial decrease of SON temperature in the 16–20 km layer of the south polar zone, presumably associated with the ozone decrease in this region in this season. The global surface temperature has also decreased in SON relative to other seasons, perhaps associated with the relative decrease of global total ozone in this season during the last decade.