Sensitivity of erythemally effective UV irradiance and daily exposure to temporal variability in total ozone.

The provision of information to the public about current levels of the erythemally effective UV radiation is an important issue in health care. The quality of promoted values is therefore of special importance. The atmospheric parameter which affects the erythemally effective UV radiation under clear sky most is the total ozone content of the atmosphere. In this paper we examined the sensitivity of the erythemally effective irradiance and daily radiant exposure to the temporal variability of total ozone on time scales from 1 to 15 days. The results show that the sensitivity is highest for the first 24 h. Larger time scales do not exhibit a similar influence. Total ozone measurements of the previous day may already cause uncertainties higher than 0.5 UV index (UVI) independent of the geolocation. For comparison, a temporal persistence of 15 days may cause uncertainties of 1.2 UVI at 50 degrees N, 1 UVI at 30 degrees S and less than 1 UVI at the equator. The results of this study allow finding the necessary temporal resolution of total ozone values when a certain accuracy for the UVI or for the purpose of sun protection is required. The results are compared with those of two preceding studies where we quantified the influence of measurement uncertainties and spatial total ozone variability to the erythemally effective irradiance at noon and to the daily dose. We conclude that temporal variability of total ozone is the most critical issue, but also measurement uncertainties do have a noticeable influence on the erythemally effective radiation.