TOTAL OZONE CHANGES OVER EURASIA SINCE 1973 BASED ON REEVALUATED FILTER OZONOMETER DATA

Since the early 1960s, on the vast territory of the former USSR, 45 st ations have been in continuous operation, utilizing the broadband filt er M-83 ozonometer. The quality of the ozone data during the first dec ade was unsatisfactory. After 1972 an improved version of the ozonomet er was introduced together with improved quality control practices, in cluding methodology of observations. The more reliable data of 1973 th rough March 1994 have been rigorously reexamined by applying variabili ty analysis, comparison with lower-stratosphere temperatures and/or ne arby Dobson stations, and overpassing TOMS for identifying concurrence or discrepancies. These control procedures together with the informat ion on instrument relocation and calibrations made it possible to reev aluate the record of all 45 stations. The accuracy of the improved ozo nometer data is about 3% for direct Sun measurements and similar to 5% for zenith sky observations; although not so good as that of the Dobs on, in the long run it provides consistent ozone data sets. This data set is now made available to the World Ozone Data Center (WO3DC), Toro nto. Thus for the first time, based on a 21-year long record, informat ion is deduced on the differences in the ozone annual cycle between Ea stern Siberia and the European part, on the strong appearance of quasi -biennial oscillation (QBO) signals especially pronounced as ozone def iciency during the western phase of the QBO, on the ozone variability, and on the long-term changes over the huge territory from Central Eur ope to the Far East. The specifics of the ozone changes considered in concurrence with the prevailing general stratospheric circulation cond itions permitted us to distinguish four broad regions with consistent ozone regimes. The appearance of the strongest northern hemisphere ozo ne maximum and a monthly mean of similar to 470 matm cm over Siberia d uring winter-spring, compared with similar to 400 matm cm over Europe, the occurrence of the ozone annual minimums as early as August over E astern Siberia, compared with October over the European part, was esta blished and is probably related to the specifics of the atmospheric ci rculation patterns. The long-term ozone changes are considered in rela tion to the stratospheric temperature at 100-hPa. For each deviation f rom the monthly normal temperature by 1 degrees C, there is a correspo nding change by the same sign 5-6 matm cm in the monthly ozone deviati ons. The calculated long-term ozone trends for 1973 through March 1994 (given in percent per decade +/-2 sigma) are as follows: European par t, -3.6+/-0.8; Central Asia, -2.0+/-0.6; Western Siberia, 3.5+/-0.8; a nd Eastern Siberia - Far East, -3.2+/-0.8. They show a steady ozone de cline similar to that deduced from the Dobson stations at the same lat itudes. The decline during the past 15 years is stronger and, in gener al, concurs with Total Ozone Mapping Spectrometer (TOMS) trends which are, however, slightly more negative.