Erythemal ultraviolet insolation in New Zealand at solar zenith angles of 30 and 45.

Solar UV radiometers with spectral responsivities that are close to the erythemal/carcinogenic action spectrum of skin have been installed at several centers of population in New Zealand, including Auckland, 37 degrees S, Wellington, 41 degrees S and Christchurch, 43.5 degrees S. The data set covers the period from the time the radiometry program commenced in 1988/1989 to the end of the southern summer, March 1995. The radiometers were recalibrated annually and the data were corrected for changes in the absolute responsivity of the radiometers. Erythemally effective UV irradiances at solar zenith angles of 30 degrees and 45 degrees were then extracted from the data set. No monotonic trend in these data is apparent, although there are statistically significant differences in mean irradiances from one year to the next. An example of this is the decrease observed in all sites following the Mt. Pinatubo eruption in June 1991. The maximum erythemally effective insolations at solar zenith angles of 30 degrees and 45 degrees were consistently lower in Christchurch than in the other two New Zealand sites. This could arise from higher levels of atmospheric turbidity and/or tropospheric ozone at this location. Also, a seasonal increase in erythemally effective UV insolation from spring to autumn was observed each year in all three New Zealand sites.