DECADAL EVOLUTION OF THE ANTARCTIC OZONE HOLE

Ozone column amounts obtained by the total ozone mapping spectrometer (TOMS) in the southern polar region are analyzed during late austral w inter and spring (days 240-300) for 1980-1991 using area-mapping techn iques and area-weighted vortex averages. The vortex here is defined us ing the -50 PW (1 PVU = 1.0 x 10(-6) K kg(-1) m(2) s(-1)) contour on t he 500 K isentropic surface. The principal results are: (1) there is a distinct change after 1985 in the vortex-averaged column ozone deplet ion rate during September and October, the period of maximum ozone los s, and (2) the vortex-averaged column ozone in late August (day 240) h as dropped by 70 Dobson units (DU) in a decade due to the loss in the dark and the dilution effect. The mean ozone depletion rate in the vor tex between day 240 and the day of minimum vortex-averaged ozone is ab out 1 DU d(-1) at the beginning of the decade, increasing to about 1.8 DU d(-1) by 1985, and then apparently saturating thereafter. The vort ex-average column ozone during September and October has declined at t he rate of 11.3 DU yr(-1) (3.8%) from 1980 to 1987 (90 DU over 8 years ) and at a smaller rate of 2 DU yr(-1) (0.9%) from 1987 to 1991 (10 DU over 5 years, excluding the anomalous year 1988). We interpret the ye ar-to-year trend in the ozone depletion rate during the earlier part o f the decade as due to the rise of anthropogenic chlorine in the atmos phere. The slower trend at the end of the decade indicates saturation of ozone depletion in the vortex interior, in that chlorine amounts in the mid-1980s were already sufficiently high to deplete most of the o zone in air within the isolated regions of the lower-stratospheric pol ar vortex. In subsequent years, increases in stratospheric chlorine ma y have enhanced wintertime chemical loss of ozone in the south polar v ortex even before major losses during the Antarctic spring.