Antarctic Ozone Hole: Possible implications for ozone trends in the southern hemisphere

Satellite‐borne instruments (the Total Ozone Mapping Spectrometer and the Solar Backscattered Ultraviolet Instrument) show that, compared to 1979, total column ozone has a year‐round decrease of more than 5% in the neighborhood of 60°S. The meteorological conditions (warmer temperatures, the absence of polar stratospheric clouds) at these latitudes do not seem to favor heterogeneous chemistry as the direct cause for the observed year‐round ozone reduction. A mechanism involving the seasonal transport of ozone‐poor air from within the polar vortex to lower latitudes (the so‐called “dilution effect”) is proposed as a possible explanation for the observed year‐round ozone reduction in subpolar regions. A two‐dimensional model with an imposed springtime Antarctic ozone depletion is used to study the post‐ozone hole impact on the spatial and temporal distributions of column ozone at latitudes north of 60°S. It is found that the time constant associated with the dilution effect in the latitude region 40°–60°S is about 1 year, long enough to contribute to the observed year‐round decrease of total ozone in that region. Because of the relatively short ozone replacement time constant (∼1 month) at latitudes north of 30°S, the calculated dilution effect over these latitudes is small. Measurement strategies aimed at distinguishing various possible causes for the observed ozone reduction at middle to high latitudes in the southern hemisphere are proposed.