四川地区云和空中水资源分布与演变

Distribution and Variation of Clouds and Water Resources in Clouds in Sichuan

利用1971～2000年台站云降水资料和NCEP再分析资料,分析了四川地区云和空中水资源的分布与演变。研究发现:四川地区平均总云量为7.2成,低云量4.7成,全年阴天日数193.5天,降水日数154.0天,小到中雨日147.1天;全年大气可降水量为181.7kg.m-2。云有明显的季节变化特征,总云量夏季最高,春季次之,冬季最低,低云量夏季最高,秋季次之,冬季最低。大气可降水量夏季最大,秋季次之,冬季最少。云和小到中雨日的空间分布具有明显的地域性,且夏季分布与全年分布显著不同。在高原上,总云和低云、降水日、小到中雨日呈相反的变化趋势,总云在平均状态附近波动略有减少,而低云、降水日、小到中雨日在平均状态附近波动略有增加;在盆地内,云和降水日的演变趋势相同,总云量、低云量、降水日、小到中雨日都在线性减少。30年来四川地区大气可降水量线性变化则略有增多。

On the basis of the 30-year ground observational cloud and precipitation data from 77 meteorological stations as well as NCEP reanalysis data,addressed are the distribution and variation of clouds and water resources in clouds in Sichuan.The analysis results indicate that annually,there were 193.5 overcast days,154.0 precipitation days,147.1 small/moderate precipitation days （0.1 to 25 mm）,with the annual precipitable water being 181.30 kg·m^-2,the total cloud cover being 7.2/10,and the low-level cloud cover being 4.7/10 over Sichuan. Cloud cover varied obviously with season：the greatest total cloud cover appearing in summer,the secondary in spring,and the least in winter; the greatest low-level cloud cover appearing in summer,the secondary in autumn,and the least in winter. Precipitable water varied also with season obviously,being the greatest in summer,secondary in autumn,and least in winter.The spatial distribution of clouds and small/moderate precipitation days differ obviously over the different parts of Sichuan,while the spatial distribution in summer was different obviously with the annual spatial distribution. In the recent 30 years,total cloud cover fluctuated around the average level with a slightly downward tendency over the plateau,while low-level cloud cover,small/moderate precipitation days,and precipitation days fluctuated around the average level with a slightly upward tendency.However,in the basin,total cloud cover,low-level cloud cover,precipitation days,and small/moderate precipitation days varied with a downward tendency.The precipitable water had an upward tendency in the 30 years.