INCREASE IN SOLAR UV-RADIATION WITH ALTITUDE

Since 1981, broad-band measurements have been made at Jungfraujoch, Sw itzerland (3576 m above sea-level (a.s.l.)) and Innsbruck, Austria (57 7 m a.s.l.), where daily totals of erythemal effective irradiance, UVA irradiance and total irradiance have been compared. Under clear sky c onditions, the observed increases in irradiance with altitude (altitud e effect) of the daily totals of global irradiance are 8% +/- 2% per 1 000 m (total irradiance), 9% +/- 2% per 1000 m (UVA irradiance) and 18 % +/- 2% per 1000 m (erythemal effective irradiance) during the summer . The altitude effect of the simultaneously measured erythemal effecti ve irradiance between Innsbruck (577 m a. s.l.) and Hafelekar (2300 m a.s.l.), horizontally separated by 2.5 km, shows a slight dependence o n the solar elevation: 15.1% +/- 1.8% per 1000 m at 60 degrees solar e levation and 18.6% +/- 2.9% per 1000 m at 20 degrees solar elevation. Simultaneously taken measurements of solar irradiance with high resolu tion spectrometers at Garrnisch-Partenkirchen, Germany (730 m a.s.l.) and Wank (1730 m a.s.l.), horizontally separated by 5 km, show a clear wavelength dependence of the altitude effect of the global irradiance : 9% per 1000 m at 370 nm increasing to 11% per 1000 m at 320 nm and 2 4% per 1000 m at 300 nm. The altitude effect of direct irradiance is c onsiderably higher than that of global irradiance at all measured wave lengths. (C) Elsevier Science S.A.