The Ratio of Convective Clouds to Stratiform Clouds and Corresponding Precipitation during the Warm Season in Eastern China

Based on hourly cloud observations at weather stations in China from 1985 to 2011, temporal and spatial distributions of convective and stratiform clouds and the ratio of convective to stratiform clouds are analyzed. Combined with merged daily precipitation data, the corresponding relations between convective (stratiform) clouds and monsoon rain belt are studied. The results indicate that in the warm season (May-September), the averaged occurrence frequency of convective clouds is 15.4% and that of stratiform clouds is 30.0% in eastern China. The ratio of occurrence frequency of convective clouds to that of stratiform clouds is greater than 1 in Guangdong, Guangxi, eastern Hainan and most areas of Guizhou Province, while it is less than 1 in other regions. The center of maximum occurrence frequency and areas of large amounts of stratiform clouds match well with the center of the monsoon rainfall. Their northward advances and southward retreats are consistent with the monsoon rain belt. This phenomenon indicates that precipitation on the monsoon rain belt is largely stratiform precipitation. On the other hand, the center of maximum occurrence frequency and areas of large amounts of convective clouds are located to the south of the monsoon rain belt. In South China and the Yangtze-Huaihe valley, changes in the occurrence frequency and amounts of convective clouds are opposite to those of stratiform clouds because the cloud types are dependent on atmospheric stratification. However, in northern China, convective clouds are positively correlated with stratiform clouds because atmospheric water vapor content is the critical factor that determines the formation and type of clouds. When the water vapor content increases in the monsoon season, the occurrence frequency and cloud cover of convective clouds and stratiform clouds both increase. If only considering the rainfall frequency, convective precipitation and stratiform precipitation coexist in southern China, but stratiform precipitation accounts for most of the precipitation in the Yangtze-Huaihe valley and North China.