Analysis on the Change of Sunshine Duration and Its Affecting Factors in the Tianshan Mountains in Recent 50 Years

In this paper,the annual and seasonal trend variation of sunshine duration in the Tianshan Mountains in China is analyzed using linear trend analysis based on the data of monthly sunshine duration,mean cloudage and precipitation from 24 meteorological stations in the mountains from 1960 to 2009.By using the method of IDW under ArcGIS,the spatial distribution of sunshine duration is analyzed so as to research the regional difference.The results show that the average annual sunshine duration in the Tianshan Mountains was significantly decreased in recent 50 years with a decreasing rate of 32.9 h/10 a.The change of seasonal sunshine duration was different,and the sunshine duration was decreased with a rate of-19.4 h/10 a in winter but increased with a rate of 0.7 h/10 a in spring.In addition,the sunshine duration in the 1960s was long in summer,autumn and winter,but short in spring.The positive anomaly of sunshine duration occurred in all seasons in the 1970s,especially in autumn.The sunshine duration was long in spring and winter but short in summer and autumn,and a negative anomaly of annual sunshine duration occurred in the 1980s.During the period from the 1990s to the beginning of the 21st century,the annual sunshine duration was short,especially in winter of the 1990s.Since the 21st,the sunshine duration was short in autumn and winter,but it was slightly increased in spring and summer.Moreover,more anomalous years of annual sunshine duration occurred in the 1960s,whereas less ones occurred in the 1990s.The results reveal that the change of sunshine duration is related to precipitation and cloudage.