Study On Surface Solar Radiation During 1957-2000 Over China

Surface solar radiation is one of the most essential variables that influence the climate and environment. Solar radiation data gained from routine meteorology observation are of extraordinary significance to the climate change research because of its long time scale and wide geography scope. However, the quality of the data has an important impact on understanding the environment and climate as well as their changes. This paper designed and programmed an integrated set of quality control procedures,which include three parts: physics threshold test for global, direct and diffuse radiation (QC1), sunshine duration test for global radiation (QC2) and the test to standard deviation of annual mean time series for global radiation (QC3). These proceduces are applied to the ground-measured daily solar radiation dataset, including global, direct and diffuse radiation from 122 stations in China from 1957 to 2000. The spatial, temporal distributions and temporal variation trends during the recent 40 years in China are analyzed base on the data that pass quality control, and then the impact of QC on the above research is analyzed. In the end, this paper also analyzed all the possible causes leading to this kind of variation trends. The main results are as follows: The percentages of global, direct and diffuse radiation, which can not pass QC1, are as the sequence as follows: 3.07%, 0.01%, 2.52%, and global radiation data that can not pass QC2 and QC3 are 0.77% and 0.49% respectively. Because the data that cannot pass QC are of low percentage, the quality control procedures will not change the solar radiation distributions and trend during the recent 40 years in China, whereas the quality control procedures are of obvious effects on eliminating the deviations of the data in some specific stations and periods. The surface global and direct radiations are of similar features in general variation. According to the annual average, these two variables decreased obviously from 1961 to 1989, and began increasing since 1990 but did not get back to their mean values during the 40 years. Global and direct radiation showed the most significant declining trend in southeast China, Sichuan and Guizhou Province, and middle and lower reaches of Yangtze River valley, and all of them declined most in winter. However, for diffuse radiation, there were no significant changes observed in general during recent 40 years. The stations of increasing and decreasing trends are interlaced, and most of the inshore stations are of increasing trend. Also, the lower reaches of Yellow River valley are the high value center. The changes in solar constant, Rayleigh scatting, permanent gas absorption and water vapor content are not the main factors of the changes observed in solar radiation. Base on the analysis of total cloud amount and surface visual range of 28 big cities during the past 40 years in China, it can be concluded that the change in total cloud amount is not the main cause of the changes observed in global radiation in most cities but only accounts for parts of the cause for a few cities, and the changes between visual range and global radiation is consistent. For the high correlation between surface visual range and aerosol loading, the variation of aerosol loading is probably the main cause for the changes of surface solar radiation. Meanwhile, it should be pointed out that the changes in cloud optical thickness and lifetime, which is caused by aerosol loading change or/and other factors, may be responsible for the changes of surface solar radiation.