M. Blumthaler et al., EFFECTS OF CLOUDINESS ON GLOBAL AND DIFFUSE UV IRRADIANCE IN A HIGH-MOUNTAIN AREA, Theoretical and applied climatology, 50(1-2), 1994, pp. 23-30
At the high-mountain station Jungfraujoch (3576 m a.s.l., Switzerland)
, measurements of the radiation fluxes were made during 16 periods of
six to eight weeks by means of a Robertson-Berger sunburn meter (UVB d
ata), an Eppley UVA radiometer and an Eppley pyranometer. Cloudiness,
opacity and altitude of clouds were recorded at 30-minute intervals. A
second set of instruments was employed for separate measurement of th
e diffuse radiation fluxes using shadow bands. The global and diffuse
UVA- and UVB radiation fluxes change less with cloudiness than the cor
responding total radiation fluxes. When the sun is covered by clouds,
the global UVA- and UVB radiation fluxes are also affected less than t
he global total radiation flux. The roughly equal influence of cloudin
ess on the UVA- and UVB radiation fluxes suggests that the reduction i
s influenced more by scattering than by ozone. Also, the share of diff
use irradiance in global irradiance is considerably higher for UVA- an
d UVB irradiance than for total irradiance. At 50-degrees solar elevat
ion and 0/10 cloudiness, the share is 39% for UVB irradiance, 34% for
UVA irradiance and 11% for total irradiance. The increased aerosol tur
bidity after the eruptions of El Chichon and Pinatubo has caused a sig
nificant increase in diffuse total irradiance but has not produced any
significant changes in diffuse UVA- and UVB irradiances.