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UV Irradiance Enhancements by Scattering of Solar Radiation from Clouds

by 1,†, 2,*,† and 3,†
1
Meteorological Observatory Lindenberg-Richard-Aßmann-Observatory, German Meteorological Service, Lindenberg 15848, Germany
2
The SETI Institute Carl Sagan Center/NASA Ames Research Center, Moffett Field, CA 94035, USA
3
Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen 91054, Germany
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editor: Robert W. Talbot
Atmosphere 2015, 6(8), 1211-1228; https://doi.org/10.3390/atmos6081211
Received: 11 June 2015 / Revised: 6 August 2015 / Accepted: 13 August 2015 / Published: 18 August 2015
Scattering of solar radiation by clouds can reduce or enhance solar global irradiance compared to cloudless-sky irradiance at the Earth’s surface. Cloud effects to global irradiance can be described by Cloud Modification Factors (CMF). Depending on strength and duration, irradiance enhancements affect the energy balance of the surface and gain of solar power for electric energy generation. In the ultraviolet region, they increase the risk for damage to living organisms. Wavelength-dependent CMFs have been shown to reach 1.5 even in the UV-B region at low altitudes. Ground-based solar radiation measurements in the high Andes region at altitudes up to 5917 m a.s.l showed cloud-induced irradiance enhancements. While UV-A enhancements were explained by cloud scattering, both radiation scattering from clouds and Negative Ozone Anomalies (NOA) have been discussed to have caused short-time enhancement of UV-B irradiance. Based on scenarios using published CMF and additional spectroradiometric measurements at a low-altitude site, the contribution of cloud scattering to the UV-B irradiance enhancement in the Andes region has been estimated. The range of UV index estimates converted from measured UV-B and UV-A irradiance and modeled cloudless-sky ratios UV-B/erythemal UV is compatible with an earlier estimate of an extreme UV index value of 43 derived for the high Andes. View Full-Text
Keywords: UV-B and UV-A irradiance; cloud modification factors; cloud scattering; high-altitude radiation measurements UV-B and UV-A irradiance; cloud modification factors; cloud scattering; high-altitude radiation measurements
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Feister, U.; Cabrol, N.; Häder, D. UV Irradiance Enhancements by Scattering of Solar Radiation from Clouds. Atmosphere 2015, 6, 1211-1228.

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