Analysis of All-China Sunshine Conditions of Site Selection for Large Solar Telescopes

The yearly and monthly data sets of sunshine duration and percent- age obtained at the 756 principal and primary standard meteorological stations all over China from 1971 to 2000, compiled by the Meteorological Reference Room of the National Center for Meteorological Information, are used to study the countrywide sunshine conditions and to analyze the factors which have an effect on the sunshine, in combination with the data of the key elements, such as the cloud cover and water vapor, recorded in China from 1951 to 2008. The obtained result shows that the distributions of the sunshine duration and sun- shine percentage in China are consistent with each other: small in southeastern China and large in northwestern China, increasing from southeast to northwest. In eastern China, the sunshine duration gradually increases from south to north and the sunshine condition in the western area is integrally better than that in the eastern area, tallying with the general rule. The sunshine condition in the Shiquanhe area in southwestern Tibet is the optimum, the sunshine conditions in the vicinity of the latitude zone of 40∘ N and in the area of southern Tibet take the second place, those in the south of the Yangtze River, in southern China, Sichuan Basin and in the eastern area of the Yunnan-Guizhou Plateau are rela- tively poor, and those in the other areas are placed in the middle. The sunshine duration is affected by the key elements like the cloud cover and water vapor, exhibiting a negative correlation with them.