A COMPARISON OF CLOUDLESS SKY ERYTHEMAL ULTRAVIOLET-RADIATION AT 2 SITES IN SOUTHWEST SWEDEN

This case study examines the variability of ultraviolet erythemal radi ation at two different but nearby locations in southwest Sweden. Data from two identical radiometers were analysed. One instrument sampled t he urbanised environment of Goteborg (latitude: 57.70 degrees N, longi tude: 12.00 degrees E), while the second one sampled a rural site, Kos ter Island (latitude: 58.83 degrees N; longitude: 11.00 degrees E), so me 143 km to the north. Both radiometers were intercompared during the field season, and one radiometer had its calibration traced to a WMO/ STUK intercomparison performed in 1995. Only cloudless data for the pe riod 1 April 1996-30 September 1996 are examined in this study. Higher depletion was reported at Koster Island for the 4 days which were sim ultaneously cloudless at both sites. A cloudless model developed by Gr een et al. (Green, A.E.S., Cross, K.R. and Smith, L.A. 1980. Photochem . Pholobiol., 31, 59-65.) was used to determine daily measured/model r atios for both sites. However there is some uncertainty in these ratio s due to the spatial variability in total column ozone. Examining seas onal trends, much scatter is reported at both sites, although after da y 226 (13 August 1996), distinctly lower ratios were reported at Koste r Island. By examining pyranometer and relative humidity data at both sites, it is argued that coastal haze at Koster Island may explain the higher depletion there. (C) 1998 Royal Meteorological Society.