The Analysis of Sunshine Conditions over China in Site Survey for Large Solar Telescope

The sunshine conditions over China are analyzed,by using the yearly and monthly data sets of sunshine duration and percentage,from 756 principal and reference climatological stations for the period of 1971-2000.With the statistics of cloundiness,the water vapor from 1951 to 2008,the factors affecting the sunshine are also analyzed.The results show that,the distribution of sunshine duration and percentage are consisitent.The values of sunshine duration and percentage in the southeast are small,and large in the northwest,and the values increase from southeast to northwest.The sunshine duration in eastern area of China increases from south to north,and the sunshine conditions in western area are better than in the east,which is consistent with the common sense.For the sunshine conditions,the southwest of Tibet is the best,followed up by the 40°N latitude band and south Tibet;South of Yangzi River,South China,the Sichuan basin as well as the area in east of Yunnan-Guizhou Plateau have worse sunshine conditions;the conditions of other regions are just all right.Sunshine duration is influenced by the cloud and water vapor,and it has a negative correlation with them.