ESTIMATING THE GLOBAL OZONE CHARACTERISTICS DURING THE LAST 30 YEARS

All available total ozone data from over 150 past and present Global O zone Observing System (Go(3)OS) stations, after careful quality contro l and reevaluation, have been analyzed in order to deduce the basic gl obal ozone characteristics both for pre-ozone-hole and during ''ozone hole'' time periods. Utilizing Total Ozone Mapping Spectrometer (TOMS) data, the longitudinal inhomogeneity of the total ozone distribution was estimated. That permitted the use of ground-based data for establi shing long-term zonal as well as hemispheric and global ozone variatio ns for the 1964-1994 period. The difference between the estimations of monthly zonal variations from ground-based and TOMS data for the over lapping period of 1979-1993 is less than 1% in latitudes 40 degrees S- 60 degrees N. The ozone changes are several times larger than possible errors of the estimated values; therefore the results are highly reli able. They show that the northern hemisphere average ozone was similar to 312 and the southern average was similar to 300 matm cm in the pre -ozone-hole decades (1964-1980) and that the global average for the 19 84-1993 period was lower by similar to 3% (from 306.4+/-1.0 down to 29 7.7+/-2.2 matm cm). The southern hemisphere contributed similar to 64% of the overall ozone decline. The levels of annual ozone maximum have been reduced by 5.8% in the southern hemisphere and 3.2% in the north ern hemisphere, and the levels of ozone minimum have been reduced by 2 .1% and 1.2%, respectively. The ozone trends for midlatitudinal bands (35-65 degrees) show a pronounced seasonal dependence varying from sim ilar to 3% to 8% (and even more for the southern hemisphere) for the c umulative decline since 1970. The ozone decline calculated in percent per decade from 1980 is almost twice as large as the decline calculate d from 1970. The cumulative year-round global ozone decline is 4.8+/-0 .6%; however, the cumulative year-round decline over middle and polar latitudes is more than 7%. The advantages of establishing ozone ''norm s'' for estimations of long-term ozone variations from ground-based da ta are emphasized.