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On the wavelength‐dependent attenuation of UV radiation by clouds
Author(s) -
Lindfors Anders,
Arola Antti
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl032571
Subject(s) - attenuation , wavelength , radiation , optics , remote sensing , environmental science , physics , geology
We studied the wavelength‐dependence of the attenuation of incoming solar UV radiation by a homogeneous cloud layer. By systematic analysis of irradiances simulated with a radiative transfer model, we were able to separate the wavelength‐dependence of the cloud modification factor into different components, and thus achieve an understanding of the physical processes involved. Our results show that short wavelengths, in general, penetrate the cloud more effectively than longer wavelengths and that there are two important contributors to this wavelength‐dependence: (1) that induced by multiple scattering between the cloud top and the atmosphere above and (2) that introduced by the wavelength‐dependent radiance distribution at the cloud top (including the direct beam) together with the transmittance of the cloud alone as function of angle of incidence. Furthermore, we found that the former does not depend on solar zenith angle, whereas the latter does and hence also introduces a solar zenith angle dependence in the wavelength‐dependence of the cloud modification factor.