Improved sky imaging for studies of enhanced UV irradiance

[摘要] A recent World Meteorological Organisation report discussed the importance ofcontinued study of the effect of clouds on the solar UV radiation reaching the earth'ssurface. The report mentions that the use of all-sky imagery offers the potential tounderstand and quantify cloud effects more accurately. There are an increasing number ofstudies investigating the enhancement of surface solar, UV irradiance, and UV actinicflux, using automated CCD and sky imagers. This paper describes new algorithmsapplicable to a commercially available all-sky imager (TSI-440), for researchinvestigating cloud enhanced spectral UV irradiance. Specifically, these include threenew algorithms relating to cloud amount at different spatial positions from 1) zenith and2) from the solar position and 3) the visible brightness of clouds surrounding the sun. Apossible relationship between UV enhancement and the occurrence of near-sun cloudbrightness is reported based on this preliminary data. It is found that a range ofwavelength dependent intensities, from 306 to 400 nm, can occur in one day for UVenhancements. Evidence for a possible decreasing variation of intensity with longerwavelengths is also presented.

[学科分类] 大气科学