Trends in Surface Solar Radiation (SSR) and the Effect of Clouds on SSR during 1961-2009 in China

This study investigates variations in surface solar radiation (SSR) and the effects of cloud on SSR during 1961-2009 based on global radiation and cloud fraction data from 100 radiation observation sites over China. The results indicate a general decrease of -4.3%/10a (7. 87 W m^-2 (10 a)^-1) in SSR over land surfaces since measurements began (in about 1961) until 1990, with a turnover corresponding to a 2.8%/10a (2.4 W m^-2 (10a)^-1) increase from 1990 onward. Moreover, this turnover was more significant in southern China. It seems that cloud was not one of the primary factors inducing global dimming during 1961-1990, based on the similar variation characteristics witnessed under all-sky and clear-sky conditions and the weak correlation between total cloud fraction and SSR. However, there were distinct differences between all-sky and clear-sky SSR results after 1990 and it shows a significant negative correlation between all-sky and clear-sky SSR values. Thus, it may be concluded that cloud had a significant effect on SSR variation, such that it may have inhibited global brightening in some way during 1990-2009.