Cloud modulation of shortwave and ultraviolet solar irradiances at surface

摘要

The cloudiness effect on solar radiation was analyzed in this study. Measurements of UV erythemal(UVER) and total shortwave (SW) radiation were registered in Valladolid, Central Spain. Simulationsby the radiative transfer model SMARTS 2.9.5 were used to calculate the cloud modification factor(CMF). The dependences of CMF (for UVER and SW ranges) on cloud cover and cloud type wereanalyzed showing a clear decreasing trend with cloud cover, which was stronger for medium cloudsthan for high ones. A similar analysis was carried out for the ratio between CMFUVER and CMFSW. Thisratio presents a clear influence on cloud cover, solar zenith angle (SZA) and cloud type. The smallestSZAs and the high clouds produce a constant trend close to the unity. However, medium and lowSZAs and medium clouds lead to higher attenuation of SW radiation.