西南地区云量变化特征

利用西南地区(云南、贵州、四川、重庆)记录较为完整的73个测站1956~2005年月平均云量资料,采用经验正交函数分析和Mann-Kendall突变检验方法,研究分析了西南地区云量的时空分布特征。结果表明:就全年而言,整个西南地区总云量的变化趋势一致,且存在着明显的年际变化特征,1990年代以后全年总云量表现出减少趋势;此外,总云量的分布在一定程度上受地形和区域气候的影响。从季节来看,夏、秋、冬季的总云量在西南地区为空间一致的变化趋势,而春季四川盆地北部总云量的变化趋势与其余地区相反;四季总云量也有明显的年际变化特征。低云量,全年和四季的时空变化特征相似,由于受地形起伏及区域气候差异的影响,川西高原东部和重庆地区的变化趋势与四川盆地的相反,且同样存在着明显的年际变化特征。另外,突变分析结果显示,西南地区的低云量近50a来呈持续减少趋势,而总云量在1990年发生突变,突变前在0线附近震荡,突变后总云量持续减少。

Variation Characteristics of Cloud Cover over Southwestern China

Based on the monthly mean cloud cover data at 73 observation stations in Southwest China from 1956 to 2005,the spatial andtemporal distributions of cloud cover were analyzed by using empirical orthogonal function （EOF）analysis and Mann - Kendall test.The results showed that the first eigenvectors of annual total cloud cover by EOF in Southwest China were negative consistently,and thetemporal coefficient of the first eigenvector of annual total cloud cover decreased after the 1990s. This means that the change trends ofannual total cloud cover were consistent,and the interannual variation was obvious. Moreover,the second eigenvectors of annual totalcloud cover were different,and the eigenvector values in the east of Southwestern China were negative and positive in the west of South western China. It means that the spatial distribution of annual total cloud cover was connected with terrain and climate to some extent.From the view of seasonal variation,the spatial distribution of total cloud cover in summer,autumn and winter was also consistent,butthat in spring was different,and the change trend of total cloud cover in northern Sichuan Basin in spring was opposite to the rest ofSouthwest China. Furthermore,the total cloud cover in four seasons appeared obvious interannual variation. The spatial and temporaldistribution of low cloud cover in four seasons and year was similar,and the change trend of low cloud cover in the east of the westernSichuan highland and Chongqing was opposite to Sichuan Basin due to the influence of terrain and regional climate. As with the totalcloud cover,the low cloud cover had obvious annual variation. In addition,the low cloud cover over southwest China decreased contin uously in past 50 years,but the total cloud cover had a decreasing mutation in 1990.