Global Analysis of Recent Total Ozone Fluctuations

Total ozone data for various regions of the world were examined on a seasonal and annual basis. The increase in total ozone noted during the 1960s appears to have ended, and at U.S. and British stations, there was a significant 2% reduction in ozone between 1970 and 1974, although the annual rate of decrease diminished from 0.7% between 1971 and 1972 to 0.2% between 1973 and 1974. In the U.S., the 2% reduction returned the total ozone value nearly to its 1963 level, but in Great Britain (and at Huancayo, Peru) the decrease amounted to only one-third (one-fifth) of the increase during the 1960s. The existence of quasi-biennial oscillation in total ozone, variable in phase, amplitude, and period, makes extremely difficult the detection of any effect upon the ozone shield resulting from the large Russian nuclear explosions in 1961 and 1962. The authors fail to find an unambiguous effect, and suggest that, on a seasonal or annual basis, these nuclear tests could not have reduced the hemispheric total ozone amount by more than 1-2%. There is no evidence of a decrease in total ozone over Japan during the passage of radioactive clouds after individual Chinese tests in 1968, 1969, and 1970. The coincidence of the breakdown of the quasi-biennial oscillation in total ozone at Aspendale and Brisbane in the exact season (spring, 1963) of the eruption of Mt. Agung (8 degrees S) is noted. For whatever reason, it appears that the Southern Hemisphere ozone values were anomalously high (or indicated to be anomalously high) after the eruption, but the lengthening of the period of quasi-biennial oscillation during this time may also be influencing, or even dominating, the results. The sunspot-total ozone relation is re-examined by using the available data. There is limited evidence of a nearly in-phase relationship; accordingly, the decrease in total ozone between 1970 and 1974 may be associated with the decrease in sunspot number after the sunspot maximum in 1969. There appears to have been some decrease in total ozone in north latitudes after the intense solar flares (solar proton events) in 1960, 1966, and 1972, but the relationship is not conclusive.