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Modification of global erythemally effective irradiance by clouds
S Thiel1, K Steiner, H K Seidlitz
1GSF-National Research Center for Environment and Health, Exposure Chambers for Plants, Germany. thiel@gsf.de
Photochemistry and Photobiology
|June 1, 1997
Summary
Clouds significantly impact UV radiation, affecting ecosystems and health. This study quantifies cloud attenuation of UV irradiance, improving risk assessments by classifying cloud types.
Area of Science:
- Atmospheric science and radiation
- UV radiation effects on ecology and human health
Background:
- Cloud modification of global radiation is a key uncertainty in UV risk assessment.
- Accurate understanding of UV irradiance is crucial for ecological systems and human health.
Purpose of the Study:
- To quantify cloud transmission of erythemally weighted irradiance.
- To assess the impact of different cloud types on UV radiation attenuation.
- To improve the accuracy of UV risk assessments by understanding cloud influences.
Main Methods:
- Measurements of global transmission using Robertson-Berger meters.
- Simultaneous observation and classification of cloud types.
- Analysis of global irradiance data and comparison with UV-specific data.
Main Results:
- Global UV irradiance transmission is strongly dependent on cloud amount, described by a cubic function.
- No significant difference was found between the attenuation of erythemal and total global radiation.
- Classifying data by cloud form provided a more accurate fit, with attenuation coefficients varying from 0.4 (high clouds) to 1.0 (cumulonimbus).
Conclusions:
- Cloud type significantly influences UV radiation attenuation.
- A quantitative parameter for cloud attenuation improves UV risk assessment accuracy.
- This research provides a more refined understanding of cloud impacts on UV irradiance.