Total ozone changes in the northern hemisphere mid-latitudinal belt (30–60°N) derived from Dobson spectrophotometer measurements, 1964–1988

A statistical analysis is presented of the daily values of total column ozone obtained during 1964–1988 from a network of 24 Dobson instrument stations located within the mid-latitudinal belt 30–60°N. The year-round-, as well as the summer- and the winter data have been analyzed to detect year-to-year changes in the annual pattern of the probability density function of total ozone (PDFTO) in the belt. Long-term variations in the PDFTO have been deduced from trend analyses of the following statistical characteristics of the annual pattern of the PDFTO: mean, standard deviation, median, 10 and 90 percentile, and the asymmetry coefficient. The trends have been calculated from a multiple regression model adjusted for serial correlations, the 11-yr solar cycle, and long-term stratospheric circulation fluctuation effects. We have found that the pattern of the PDFTO has been drifting uniformly (without changes in its shape) towards lower ozone values, with some seasonal peculiarities in the drift (the annual rate of total column ozone loss). The winter pattern of the PDFTO moves (with a drift of 2.3% per decade) towards lower ozone values faster than the year round pattern (drift equals 1.8% per decade) and the summer pattern of the PDFTO (drift equals 1.5% per decade).