Variation and influential factors of total cloud amount all over China

Objective—To analyze the spatio-temporal variation,trend and influential factors of total cloud cover in China.Methods—Based on 360stations all over China during the period of 1951~ 2009,using linear trend estimation and correlation analysis method are adopted.Results—The largest total cloud amount is located in Southwest China and South China while the least in the north part of China where there is rare rainfall.In the north of about 35°N,the total cloud amount locates decreases with the increase of latitude from the south to the north,and in the south of about 35°N,the cloud amount at the same latitude in the east is more than that in the east.The total cloud amount reduced dramatically in the 1990sand the first decade of the 21st century.The obvious reduction in the total cloud amount appeared in Northeast China,southwest Tibet,Shandong and the northern region in Anhui.There is a significant positive correlation between the total cloud amount in most parts of China and relative sunspot number,precipitation,relative humidity and maximum snow depth,while there is a significant negative correlation between the evaporation capacity and the total cloud cover. Conclusion—The total cloud amount shows a downward trend over the past 59years.Climate factors have an important influence on the changes of total cloud cover.