Duration of Antarctic ozone hole a significant factor in UV levels

New studies indicate that the duration of the ozone hole can be just as significant as the size of the hole. Recent records indicate that despite the record ozone loss over Antarctica in 2000, the impact on New Zealand was less severe than in 1998, because the 2000 hole had broken up by the end of November. In 1998, this didn’t happen until Christmas, coinciding with when the sun is highest in the sky and UV penetration is greatest, and large numbers of New Zealanders are outside.

This year’s hole reached a maximum size of just over 26 million square kilometres in

mid-September, and it still occupies more than 20 million square kilometres, according to Dr Stephen Wood, of New Zealand’s National Institute of Water and Atmospheric Research (NIWA), who is currently at Scott Base, New Zealand’s Antarctic research station. He told edie that last year the hole reached 30 million square kilometres in area, and the minimum ozone reading was 126 Dobson units at Scott Base, whereas this year’s minimum was 132 units. Also, by this time last year, the hole was already five million square kilometres smaller than the hole is now.

Large year-to-year variations in the severity of the ozone hole can be caused by differences in the polar vortex – a band of strong winds that effectively keeps the atmosphere above Antarctica isolated during winter. Changes in the polar vortex are subject to planetary-scale wave motions which distort or move them around from year to year, explained Dr Wood. Last year, features of the vortex led to an early formation of the ozone hole and a very early break up. This year the vortex and the hole appear to be much more stable and circular, which suggests that the hole will probably last longer – into November and possibly even into December.

Break-up of the ozone hole has also been found to reduce ozone levels throughout the

Southern Hemisphere. This dilution accounts for about half of the 15% increase in peak summertime UV levels that have occurred in the last 20 years over New Zealand”, said Dr Wood.