Relationships between East Asian Summer Monsoon Activities and Cloud Types

The standardized precipitation index and two types of cloud indices are defined based on the pentad averaged precipitation data and ISCCP (International Satellite Cloud Climatology Project) D1 cloud data from 1998 to 2007. It is found that the precipitation index is a good indicator of East Asian summer monsoon activities, and the cloud indices can reflect well the cloud amount of deep convection (DC), altocumulus (Ac) and cumulus (Cu). Based on the climate characteristics of precipitation, combined with the division of climate in China (temperature zones, wet and dry areas) and topography of different regions, the area of continental China influenced by the East Asian monsoon is divided into five sub-regions from south to north. Correlation between monsoon activities (MA) and cloud types, as well as the relationship between the precipitation index and two types of cloud indices are studied separately in five sub-regions on pentad time scales. It is found that DC and cirrostratus (Cs) have significant positive correlations with MA in the five sub-regions, indicating that the monsoon occurs mainly with convective cloud. Ac and Cu have significant negative correlations with MA, indicating the active stage of the summer monsoon with the produced Ac and Cu. Stratus (St) and stratocumulus (Sc) have strong positive correlations with MA in North China but negative correlations in South China, respectively, which shows the characteristic of convective cloud in South China and a mixture of convective cloud and stratiform cloud in North China. Altostratus (As), cirrus (Ci) and nimbostratus (Ns) have no robust correlations with MA.