Atmos. Chem. Phys. Discuss., 4, 6213-6238, 2004
www.atmos-chem-phys-discuss.net/4/6213/2004/
doi:10.5194/acpd-4-6213-2004
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Improved sky imaging for studies of enhanced UV irradiance
J. M. Sabburg1 and C. N. Long2
1Centre for Astronomy, Solar Radiation and Climate, Faculty of Sciences, University of Southern Queensland, Toowoomba, Australia
2Pacific Northwest National Laboratory, Richland, WA, USA

Abstract. A recent World Meteorological Organisation report discussed the importance of continued study of the effect of clouds on the solar UV radiation reaching the earth’s surface. The report mentions that the use of all-sky imagery offers the potential to understand and quantify cloud effects more accurately. There are an increasing number of studies investigating the enhancement of surface UV irradiance, and UV actinic flux, using automated CCD and sky imagers. This paper describes new algorithms applicable to a commercially available all-sky imager (TSI-440), for research investigating cloud enhanced spectral UV irradiance. Specifically, these include three new algorithms relating to cloud amount at different spatial positions and the visible brightness of clouds surrounding the sun. A possible relationship between UV enhancement and the occurrence of near-sun cloud brightness is reported. It is found that a range of wavelength dependent intensities, from 306 to 400 nm, can occur in one day for UV enhancements. Evidence of a decreasing variation of intensity with longer wavelengths is also presented.

Citation: Sabburg, J. M. and Long, C. N.: Improved sky imaging for studies of enhanced UV irradiance, Atmos. Chem. Phys. Discuss., 4, 6213-6238, doi:10.5194/acpd-4-6213-2004, 2004.
 
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