Figure 7.3 Column O, versus equivalent latitude averaged over October I to 15. 1979, 1992, and 1996. Equivalent latitude is calculated from NCEP balanced winds on the 465 K potential temperature surface. Column O, measurements are version 7 Nimbus 7/TOMS data for 1979 and 1992 and EPTOxMS data for 1996.
In the rest of this chapter we discuss the physical processes that lead to the formation of the ozone hole. We will initially focus on the Antarctic, and then turn our attention to polar O, loss in the Arctic.
The first step in the formation of the Antarctic ozone hole is the formation of the polar vortex [ 187J. During the winter the Antarctic region experiences 24 h of darkness every day. There is no heating by absorption of solar ultraviolet radiation during this time. Emission of thermal radiation, however, continues, causing the Antarctic lower stratosphere to cool (Figure 7.4). The resulting cold polar temperatures coupled with relatively warm temperatures in the mid-latitudes causes a strong pressure gradient to form between the polar and mid-latitude regions. Because of the coriolis force, this north-south pressure gradient creates a zonal (east- west) wind.
Figure 7.5 shows contours of the zonal wind velocity. Note the region of high wind velocities near 60°S. Such a region of high wind velocity is often referred to as a "jet", and the jet near 60°S is known as the "polar night jet". The polar night jet extends vertically from about 100 hPa to the upper stratosphere, reaching a
Day No. of 1992
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