ATTENUATION OF ERYTHEMAL EFFECTIVE IRRADIANCE BY CLOUDINESS AT LOW AND HIGH-ALTITUDE IN THE ALPINE REGION

The transmittance of cloudiness was examined for the daily totals of g lobal erythemal effective irradiance and global total irradiance in In nsbruck (577 m above sea level [a.s.l.], Western Austria) for the peri ods 1981-1988 and 1993-1994 and at Jungfraujoch (3576 m a.s.l., Switze rland) for the period 1981-1990. The influence of varying cloudiness o n the daily totals of global erythemal effective irradiance is conside rably greater than the influence of varying ozone, The lowest transmit tance for daily totals of global erythemal effective irradiance is 9.4 % in Innsbruck (577 m a.s.l.) and 23.5% at Jungfraujoch (3576 m a.s.l. ); the median and the 25-75 percentile range at 10/10 cloudiness are 4 1.8% (28.9-56.7%) and 76.8% (63.5-86.1%), respectively. The greater tr ansmittance of global erythemal effective irradiance at Jungfraujoch o riginates from smaller thickness of the cloud layer in high mountains than in valleys. Similar transmittances were obtained for the daily to tals of global total irradiance (300-3000 mm) as a function of cloudin ess.