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Modification of Global Erythemally Effective Irradiance by Clouds
Author(s) -
Thiel Stephan,
Steiner Karl,
Seidlitz Harald K.
Publication year - 1997
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1997.tb07956.x
Subject(s) - irradiance , environmental science , cloud computing , attenuation , cloud cover , meteorology , atmospheric sciences , transmission (telecommunications) , term (time) , geography , computer science , geology , physics , optics , telecommunications , quantum mechanics , operating system
The role clouds play in the modification of global radiation is still a major uncertainty in the risk assessment of UV effects on ecological systems and human health. This study presents cloud transmission data obtained from measurements with Robertson‐Berger meters and simultaneous cloud observations. The global transmission of erythemally weighted irradiance depends strongly on cloud amount and can be described by a cubic function. The comparison with results derived from long‐term records of total global irradiance indicates no statistically significant difference between the attenuation of ery‐themal and total global radiation. The large variance of data results from lumping together data from different cloud types. Classification of data according to cloud forms yields a more statisfactory fit. The coefficient of the cubic term characterizes the ability of various cloud forms to attenuate UV radiation. It varies between 0.4 for high clouds and approximately 1.0 for cumulonimbus. This attenuation parameter allows a quantitative description of the cloud influence on irradiance and therefore a more accurate risk assessment.