Ozone and UV radiation over New Zealand

NIWA scientists have applied statistical techniques to predict ozone levels, and hence the UV levels, that may be expected over New Zealand for the coming summer.

4 December 1998

Since the 1970s the summertime ozone over New Zealand has shown a steady decline due to increasing concentrations of man-made chlorine and bromine compounds, but with significant year-to-year variability. The NIWA statistical model incorporates known sources of ozone variability, and has been validated by comparing predictions with actual measurements of ozone above Lauder, Central Otago, over the past two decades.

For the forthcoming summer (December 1998 through February 1999), the mean ozone over the NIWA Lauder observatory is expected to be between 270 and 275 Dobson Units (DU), which is only slightly less than that for last summer, but about 30–35 DU less than in the 1970s, before the effects of ozone depletion began to be seen in New Zealand. These ozone amounts are significantly less than at corresponding northern latitudes, but more than in the tropics. The global mean for ozone is about 300 DU.

Based on these ozone amounts, and on recent measurements of UV radiation in the north and south of the country, we can estimate the peak levels of sunburning radiation that may be expected over the country this summer. In northern New Zealand the peak UV Index will be 13 or more, while in the south of the country the peak values will be closer to 12. These values are 10–15% greater than they would have been in the 1970s and are also significantly larger than at corresponding latitudes of the Northern Hemisphere.

UV Index values greater than 10 may be considered extreme. During summer, the UV Index can exceed 10 between about 11:30 a.m. and 3:30 p.m. or longer. Even outside this midday period, UV intensities can be large enough to cause skin damage (e.g., sunburn) after periods of exposure shorter than 30 minutes. At high elevations, larger UV Index values are expected.

While the peak values of UV Index are relatively easy to predict, the cumulative dose of UV over the summer will depend strongly on other factors, most notably the cloud cover. This is much more variable from location to location, and is much more difficult to predict.

Current ozone and UV information is available to the public at no charge through the Internet. See, niwa.co.nz/services/uvozone/.