重庆主城区云量变化特征

Variation Characteristics of Cloud Amount Over the Main Urban Area of Chongqing

利用1951-2011年重庆沙坪坝站的总云量、低云量、平均气温、降水量、日照时数和相对湿度等气象资料,采用趋势分析、小波及相关等方法分析了重庆主城区总云量和低云量的变化特征及其与主要气象要素的关系,结果表明:整个时间域内主城区年及春、夏、秋三季的总云量总体减少,其中秋季减少最为明显,而冬季则略有增加的趋势;年及四季的低云量总体呈增加趋势,夏季和冬季增加相对明显.低云量的年际变化幅度大于总云量,但两者年际和年代际变化趋势比较一致,阶段性特征大体上体现为20世纪50年代至70年代云量相对偏少,80年代至90年代相对偏多,之后至今处于相对偏少的阶段.总云量年及各季节(除夏季外)均在20世纪90年代发生转折;而低云量年及各季发生了2次转折,分别在1964年和2005年前后(夏季除外).总云量1月、2月、10月和12月较多,8月最少;低云量最多的是12月,8月最少.总云量和低云量冬季最多,其次为秋季和春季,最少的是夏季.总云量和低云量与平均气温、日照时数和相对湿度等气象要素关系显著,但与降水量的关系总体不太明显;冬季云量和平均气温等气象要素的相关不太显著,其它季节云量和平均气温、日照时数及相对湿度显著相关.

The meteorological data recorded at Shapingba Meteorological Station of Chongqing about total/ low cloud amount, average temperature, rainfall, sunlight hours and relative humidity from 1951 to 2011 were used in wavelet analysis, linear trend analysis and correlation analysis to study the variation characteristics of cloud amount over the main urban area of Chongqing and its relationship with the main meteorological elements. Throughout the time domain, the annual total cloud cover and seasonal total cloud cov- er in spring, in summer and, especially, in autumn were generally reduced, while winter cloud cover showed a trend of slight increase. On the whole, annual and seasonal low cloud cover showed an increasing trend, especially in summer and winter. The amplitude of inter-an.nual variation of low cloud cover was greater than that of total cloud cover, but their inter-annual and inter-decadal variations were consistent. Cloud coverage was relatively low from the 1950s to the 1970s but increased from the 1980s to the 1990s and dropped thereafter. A turn occurred in total cloud cover in the 1990s and two turns occurred in low cloud cover in 1964 and 2005, respectively. The total cloud covers were maximum in January, February, October and December and minimum in August, whereas the low cloud covers were maximum in Decem- ber and minimum in August. Winter had the maximum total and low cloud covers, followed by autumn and spring, and summer had the minimum. The total and low cloud covers were associated significantly with such meteorological factors as average temperature, sunlight hours and relative humidity and non-significantly with precipitation. The cloud amount was non-significantly related to average temperature and other meteorological elements in winter, but significantly associated with average temperature, sunlight hours and relative humidity in other seasons.