Factors affecting solar UV radiation changes: a study of the new Robertson-Berger meter (UV-biometer model 501A) and Brewer data records taken at Belsk, Poland, 1993-1994

Daily doses of the erythemal solar ultra violet radiation (SUVR) reaching the ground at Belsk, Poland (52 degrees N, 21 degrees E) measured by a Brewer spectrophotometer and a UV-biometer model 501A during 1993-1994 in conjunction with daily total ozone and integrated global solar radiation observations are examined to infer their associations under all sky conditions. The observed doses are normalized using the SUVR daily doses obtained from a parametric model (a modified Bird and Riordan (1986) model). The daily variations of the normalized SUVR doses by the Brewer spectrophotometer and UV-biometer appear to be in harmony (the correlation coefficient is 0.99). A regression model is fitted to the normalized erythemal SUVR to delineate the impact of total ozone and clouds/aerosols on the SUVR. The model explains about 95% of the variance in the normalized SUVR doses and it may constitute an efficient diagnostic model for day-to-day variations of daily doses of the erythemal SUVR. It is found that the ratio of the daily value of integrated global solar radiation measured on a horizontal surface to its clear sky representative (from the Bird and Riordan (1986) model) can be used as a characteristic of the surface SUVR changes induced by atmospheric transparency changes (caused by clouds and aerosols). In view of the model's results it seems possible that daily doses of the erythemal SUVR at ground level are less sensitive to the ozone changes during overcast days than those during cloudless days; participation of the SUVR in the integrated global solar radiation is almost the same during clear-sky and overcast days. (C) 1997 Elsevier Science Ltd.