Summary

In this paper, we analyze global, direct and diffuse solar radiation data on a horizontal surface observed at stations in Shanghai, Nanjing and Hangzhou for the period of 1961 to 2000. The data include monthly averages of the daily clearness index (G=G0: the ratio of global to extra-terrestrial solar radiation) and the diffuse fraction (D=G: the ratio of diffuse to global solar radiation. The present study has processed and analyzed the data, including variables or statistics of mean, and annual monthly and daily total, the diurnal variation and the frequency of daily totals of global solar radiation. A correlation be-tween daily values of clearness index and diffuse fraction is obtained and recommended correlation equations were calculated. The annual variations and trend of yearly series are analyzed for daily global, direct and diffuse radia-tion on a horizontal surface, as well as for daily clear-ness index and diffuse fraction in Shanghai, Nanjing and Hangzhou. The results show: 1) the east China is charac-terized by a decrease in global and direct radiation and a little increase in diffuse radiation and a negative linear relationship was obtained between clearness index and dif-fuse fraction. 2) The annual variations of global, direct and diffuse radiation for Shanghai, Nanjing and Hangzhou are similar with relative low values of global and direct radiation in June due to the Meiyu period. 3) The acceler-ation of air pollution and decrease of relative sunshine are the possible causes for the decrease of global and direct radiation. 1