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Year

Figure 7.1 Area of the Antarctic o/.one hole between October 1 and October 15 of each year versus year. By convention, the size of the ozone hole is defined to he the average area enclosed by the 220 DU contour. Column O, data are version 7 TOMS data.

above 300 DU in October. During the 1980s and 1990s, column O, decreased rapidly. By the mid-1990s, column O, in this region was only about one-third of its 1950-1960s value.

Figure 7.2 also shows that the increases in size and depth of the Antarctic ozone hole correspond well with the growth of the tropospheric abundance of CFC F11 (CC1,F), which is a primary contributor to stratospheric Clv. Farman et al. [ 12] used this correlation to suggest correctly that the ozone hole was the result of the buildup of chlorine in the stratosphere.

Figure 7.3 show the anatomy of the Antarctic ozone hole. The distribution of early spring ozone shows the same overall shape in all years: there is a maximum in column ozone around 55°S (the "subpolar maximum"), with column ozone decreasing toward the pole. This overall distribution, a subpolar maximum surrounding a polar minimum, is caused by the circulation of the southern hemisphere and is not related to O, chemistry.

In October 1979, considered representative of the atmosphere prior to the ozone hole, the subpolar maximum in the column O, is ~370 DU, while the polar minimum is ~30() DU. By the mid-1990s, the subpolar maximum had decreased little, if any, but the polar minimum had decreased to 150-170 Dli, a decrease of nearly 50%. And individual measurements of column ozone of ~100 DU or less were observed 114], Thus, we see that the Antarctic ozone hole is a deepening of an already existing polar ozone minimum.

Year

Figure 7.2 High-latitude southern hemisphere column O, observed in October versus year. Solid symbols are satellite measurements, and are the value of the minimum grid point of the October monthly average column O, fields. Circles are Nimbus 7 and METEOR TOMS: triangles are Nimbus 4/BUV. Crosses are the October averages from the British Antarctic Survey's Dobson instrument at Halley Bay. The solid line is global average tropospheric F11 (CC1,F) abundance (from NOAA CMDL).

Year

Figure 7.2 High-latitude southern hemisphere column O, observed in October versus year. Solid symbols are satellite measurements, and are the value of the minimum grid point of the October monthly average column O, fields. Circles are Nimbus 7 and METEOR TOMS: triangles are Nimbus 4/BUV. Crosses are the October averages from the British Antarctic Survey's Dobson instrument at Halley Bay. The solid line is global average tropospheric F11 (CC1,F) abundance (from NOAA CMDL).

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