Global Ozone Variations: An Update into 1976

Total ozone variations have been updated into 1976 for five data regions in north temperate latitudes, as well as for the five climatic zones, both hemispheres, and the world. In the Northern Hemisphere we find a significant (at the 95% level) 5% increase in total O3 between the early 1960's and 1970, an apparent decrease of 1–2% between 1970 and 1972, and no appreciable change thereafter, though relatively low values were observed in early 1976. In the Southern Hemisphere there was perhaps a 2% increase in total O3 between 1960 and 1968, and a 1% decrease thereafter, but because of the small data sample neither trend approaches significance. The out-of-phase relation between the quasi-biennial oscillation in total O3 in the tropics and midlatitudes persists, with the biennial oscillation particularly clearcut in south temperate latitudes (except after the eruption of Mt. Agung). Umkehr data suggest about an 8% increase in ozone in the 32–46 km layer in north temperate latitudes between 1962 and 1973 (the years before the eruptions of Mt. Agung and Volcano Fuego, respectively), and only a slight, and apparently temporary, decrease after 1974. Thus, any fluorocarbon effect on ozone amount in this layer apparently is being overwhelmed by natural processes, assuming the Umkehr data are representative and basically correct. The indicated decrease of O3 in this layer following the eruptions of Agung and Fuego is probably mostly fictitious and due to errors in the Umkehr method induced by aerosols of volcanic origin.