Abstract:

Based on the data of cloud amount during 1951－2007 from seven weather stations in Tianshui，the variation of the total cloud amount and low cloud amount was analyzed，and also the relationship between cloud amount and interrelated climatic factors was discussed．The results showed that the mean total amount of cloud varied little and mean amount of low cloud increased by 0．25%every ten years since 1951．The rainy days with different rainfall level correlated well with cloud amount．It also indicated that the precipitation varied with cloud amount，the annual precipitation increased by 156 mm when annual mean cloud amount increased by 10%．
When seasonal mean cloud amount increased 10%，the precipitation increased by 25 mm，75 mm，35 mm and 3．8 mm in spring，summer，autumn and winter，respectively．When the cloud amount increased by 10%，the mean temperature in spring and summer decreased by 0．6℃and 0．5℃，but there was no correlation between cloud amount and mean temperature in winter and autumn．The sunshine hours was seriously influenced by cloud amount，when cloud amount increased by 10%，the sunshine hours decreased by 102．2 h in spring，90．8 h in summer，87．7 h in autumn and 65．3 h in winter．There was positive correlative between mean cloud amount and relative humidity，when cloud amount increased by 10%，the relative humidity increased by 4%in summer，3%in spring，autumn and winter．The days with＞80%cloud amount reduced year by year in spring．

Key words: Tianshui, cloud amount, variation, climatic factors, influence

摘要：

云是气候变化的重要因子之一，为了探究甘肃天水市地区的云量的变化特征，用境内7个气象站1951～2007年近60 a的云量观测资料分析总、低云量变化特点及与相关气候因子的关系。结果表明，自1951年以来该地平均总云量稳定性较好，平均低云量以0．25成/10 a的速度递增。各级降水日数及云量相关性较显著。不同时段的降水量随云量变化比较明显。年平均总云量增加1成，年降水量增加156 mm，春季平均总云量增加1成，降水量增加25 mm;夏季平均总云量增加1成，降水量增加75 mm;秋季平均总云量增加1成，降水量增加35 mm;冬季总云量增加1成，降水量增加3．8mm。平均云量与气温的相关性时段性较强，云量增加1成，春季和夏季的平均气温分别降低0．6℃和0．5℃，秋季和冬季的气温与平均云量线性相关不显著。云量对日照的影响最为直接，云量增加1成，春季总日照时数减少102．2 h，夏季减少90．8 h，秋季减少87．7 h，冬季减少65．3 h。平均云量与相对湿度呈显著正相关，云量增加1成，夏季平均相对湿度增加4%，春、秋、冬季增加3%。

关键词: 云量, 变化, 气候因子, 影响, 天水