Properties of Solar Radiation over Chinese Arid and Semi-Arid Areas

Climatic characteristics of broadband solar radiation (R-s) in Chinese arid and semi-arid areas are reported in this study. The annual average daily R-s in the arid and semi-arid areas is 16.3 +/- 5.77 and 15.3 +/- 5.16 MJ m(-2) d(-1), respectively. The highest value (17.2 +/- 5.84 MJ m(-2) d(-1)) appears in an arid area at Linze. The lowest value appears in the semi-arid area of Ansai. Pronounced seasonal variation of R-s is observed with the highest value in summer and the lowest in winter. The clearness index showed similar seasonal pattern at most sites, with the minimum observed in the summer and the highest values in winter at both arid and semi-arid areas. The seasonal variation of the ratio of R-s to its extraterrestrial value K-t in the arid area is more significant than that observed in the semi-arid region, and it is caused by the different range of variation of water vapor between arid and semi-arid areas. The seasonal fluctuations in R-s and K-t are mainly controlled by the water vapor content in these areas. The aerosol particles have significant influence on R-s and K-t at stations with higher aerosol burden.