Analysis on Variation of Sunshine Hours in Xilinhaote City

The variation of sunshine hours was analyzed by using climate trend method based on the data of sunshine hours,total cloud amount,low cloud cover,precipitation and vapor pressure from 1961 to 2010 in Xilinhaote city.The results showed that annual sunshine hours increased significantly(P0.01).Furthermore,annual mean sunshine hours in decades from 1960s to 1990s increased and up to maximum value in 1990s,and decreased after the year of 2000.Sunshine hours in summer increased significantly(P0.01).There were less sunshine hours in each season during 1960s and 1970s,and more sunshine hours in each season during 1980s to 2000s.Sunshine hours of each month increased fluctuately,and up to peak value in August.There was an abrupt change in 1985,which resulted from seasonal abrupt change,particularly in spring and summer.Besides,cloud amount was an important factor affected sunshine hours,and the increase of sunshine hours had a close relationship with vapor pressure in summer and winter,and precipitation in summer and autumn.