中国夏季云和降水的定量关系及其成因分析

Quantitative Relationship Between Cloud Amount and Precipitation in Summer over China and its Causes

云的形成是产生降雨的必要条件,云和降水之间存在着极为密切而复杂的联系。利用常规站点数据和ISCCP卫星数据等资料分析了夏季中国地区云的多种特征参数的变化与降水变化在时空分布上的联系。站点数据结果表明总云量、低云量与降水的距平在全国范围内表现出显著的正相关关系;在通过0.05水平显著性检验的站点上,云量和降水距平百分率之间的线性关系较明显,总云量每增加1.00%降水增加2.23%,低云量每增加1.00%降水增加0.46%。ISCCP数据结果显示总云云量、光学厚度和云水路径以及高云中的卷层云和深对流云云量与降水距平呈非常好的正相关关系。采用K-means聚类分析方法并参考中国地理气候分布特点,将中国分为9个气候区,以小波相干分析和交叉小波分析对各个气候区夏季云量和降水距平百分率序列在时频域内多尺度特征的关系做了进一步研究。结果显示9个气候区夏季白天总云量和低云量与降水变化在2~4年(a)和5~8 a的尺度周期都具有较强的相干性与共振周期,且处于正相关位相。在时空分布和时频域上,中国地区夏季云和降水的变化之间都存在非常显著的正相关关系,尤其是低云量。云和降水变化之间具有强相干性与共振周期是两者之间正相关联系的原因。

One of the requirements for producing rainfall is cloud formation,and clouds and precipitation have a very intricate and intimate relationship.First,we used databases from conventional stations and ISCCP(International Satellite Cloud Climatology Project)to evaluate the spatial and temporal relationships between the variation of several characteristic features of clouds and the variance in summertime precipitation over China.According to the station dataset's findings,there is a significant positive correlation between the anomalous percentage of total cloud cover,low cloud cover,and precipitation across the entire nation.For stations that pass the 0.05 level significance test,the linear relationships between the anomalous percentage of clouds and precipitation are particularly obvious.For every 1.00%increase in total cloud cover,precipitation increases by 2.23%,and for every 1.00%increase in low cloud cover,precipitation increases by 0.46%.The ISCCP dataset results demonstrate very strong positive connections between abnormal percentages of cloud amount,optical thickness,cloud-water path,cirrus and deep convective cloud amount in high clouds,and that of precipitation.Second,China was divided into nine climate zones using the k-means cluster analysis method and with reference to the geoclimatic distribution of China.Then wavelet coherence analysis and cross wavelet analysis were used to further investigate the relationship in the time-frequency domain between the anomalous percentage of cloud amounts and precipitation in each climate zone.The findings demonstrate substantial coherence and resonance cycles at the scales of 2 to 4 years and 5 to 8 years,and a positive correlation phase for the anomalous percentage of total and low cloud quantities and daytime precipitation in summer throughout the nine climate zones.In both time-space distributions and time-frequency domains,there are extremely significant positive correlations between the anomalous percentage of cloud amounts(especially the low cloud amount)and precipitation in summer over China.The strong coherence and resonance period between anomalous percentage of cloud amounts and precipitation are the reasons for the positive correlation between them.