CHANGES IN OZONE TRENDS OVER THE NORTHERN-HEMISPHERE MIDDLE LATITUDES DURING THE PERIOD 1970-1990

Composite time series combining the results of total ozone measurements taken at Dobson stations located within the latitude band 30-degrees-N 60-degrees-N, in Europe, and North America, have been examined in order to detect any trends. Various regression trend models were used to identify any trend variations over the regions during the period 1970 1990. The results of fitting the models to the data imply that the model which assumes a linear trend provides precise information about the long-term ozone trends (trends during the period 1970-1990). The study identifies short-term summer trends in the 1980s that are evidently more strongly negative than trends that occur in the 1970s (the differences are statistically significant at the 2sigma level). The year-round loss (in all analyzed regions) and the winter loss in total ozone (the belt 30-degrees-N-60-degrees-N) N. America, during the 1980s are about 2-3 times higher than the losses during the 1970s (the differences are statistically significant at the 1sigma level).