1 November 2005 Factors affecting changes of spectral UV irradiance at the Sonnblick Observatory (3106 m, Austria)
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Abstract
Factors affecting changes of spectral UV irradiance at the Sonnblick Observatory are studied. Spectral UV measurements at wavelengths from 290 nm to 400 nm performed during the period from 1994 to 2003 are used in this investigation. These measurements have been performed with a Brewer ozone single spectrophotometer and with a Bentham DM 150 spectroradiometer (double monochromator). The radiative transfer model DISORT (based on the Discrete Ordinate Method) was used in the simulations. Measurements of UV-radiation at Sonnblick at 305 nm under clear sky conditions show, that the snowline may influence the irradiance by mean by 24%. Cloudiness enhances the influence of the albedo since multiple reflections between surface and lower bond of the clouds become more probable. In presence of 8/8 cloud cover, UV irradiance at 305 nm is enhanced by a factor of 1.7 when the snowline is 800 m instead of 3000 m. In addition to the snowline, clouds situated below the Sonnblick are responsible for increased albedo and consequently increased radiation. Model calculations show that average albedo is increased by 0.28 ± 0.15 due to 4/8 cloud cover or more below the top of the mountain. The influence of ozone, albedo and clouds on UV variability is evaluated separately using 10-year climatology. It was found that the effect of total ozone on short- term variability of UV irradiance at 305 nm can be more than 200% and on average 56%. Clouds can cause variability of 150% or more and on average 35%.
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Stana Simic, Philipp Weihs, H. Kromp-Kolb, A. Vacek, W. Laube, "Factors affecting changes of spectral UV irradiance at the Sonnblick Observatory (3106 m, Austria)", Proc. SPIE 5979, Remote Sensing of Clouds and the Atmosphere X, 597927 (1 November 2005); doi: 10.1117/12.627414; https://doi.org/10.1117/12.627414
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