The dependence of the surface solar irradiance on cloud and aerosol

To quantify radiative forcing of aerosol and to investigate the dependence of the horizontal UV, visible and NIR on total optical depth (TOD) and cloudiness, narrowband surface solar irradiances were measured and analyzed for direct and diffuse component. A MFRSR (Multifilter Rotating Shadowband Ratiometer) was used to measure the global, direct and diffuse solar irradiances at one broadband of 391-955 nm and 6 narrowband channels of 412.8,495.2,611.9,672.2,869,936.6 nm for a year from Jan. to Dec. in 2006 at Yonsei University in Seoul and a UV-MFRSR was used to measure irradiance at 7 narrowband channels of 299.1,304.5,310.7,317.1,323.8,331.3, 367.4 nm in UV range during 7 months at the same location with the MFRSR. It is found that the changes of solar components are closely related with the sky conditions, represented by TOD which represents cloud condition. Each solar irradiance component is investigated to analyze the dependence on TOD. With the Langley method applied for the clear-sky, extraterrestrial-normal solar irradiance, and TOD and aerosol optical depth (AOD) are calculated. Respective contributions to TOD, Rayleigh scattering optical depth, ozone absorption optical depth and AOD, were investigated as a function of wavelength. Sensitivities were tested and analyzed to quantify the effect of ozone and aerosol on direct solar irradiance, which shows higher sensitivity at shorter wavelength than at longer. In contrast, the diffuse radiation showed higher sensitivity at longer wavelength than at shorter. The global radiation showed decrease at all wavelength for AOD increase where the sensitivity was the highest at UV wavelengths.