European light dosimeter network (ELDONET): 1998 data

The European light dosimeter network of over 40 stations has been establish ed in Europe and other continents equipped with three-channel filter dosime ters to measure solar radiation in three channels, UV-B (280-315 nm), UV-A (315-400 nm) and photosynthetically active radiation (PAR). The recorded da ta have been evaluated, and the monthly doses in all three channels show a strong latitudinal dependence from northern Sweden to the Canary Islands. T here are a few remarkable exceptions such as the data recorded at the high mountain station on the Zugspitze (German Alps) and unequal doses at statio ns at comparable latitudes which indicate the impact of local weather condi tions and mean sunshine hours. While generally peak values are recorded in the months of June and July, the UV-B maxima are shifted later into the yea r, which is due to the antagonistic functions of decreasing solar angles an d increasing transparency of the atmosphere as the total column ozone decre ases in the second half of the year for the Northern Hemisphere. This is su pported by comparison with modelled total column ozone and satellite-based measurements. Also the ratios of UV-B:UV-A and UV-B:PAR as well as UV-A:PAR peak during the summer months, with the exception of the northernmost stat ion at Abisko (north Sweden) where the UV-A:PAR ratio peaks in the winter m onths which is due to the specific photoclimatic conditions north of the po lar circle. The penetration of solar radiation into the water column was fo und to strongly depend on the transparency of the water column. In Gran Can aria more than 10% of the surface UV-B penetrated to 4-5 m depth. The path of the solar eclipse on 11 August 1999 could be followed in several station s with different degrees of occlusion of the sun disk.