Seasonal variation and physical properties of the cloud system over southeastern China derived from CloudSat products
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Based on the National Centers for Environmental Prediction (NCEP) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) data and CloudSat products, the seasonal variations of the cloud properties, vertical occurrence frequency, and ice water content of clouds over southeastern China were investigated in this study. In the CloudSat data, a significant alternation in high or low cloud patterns was observed from winter to summer over southeastern China. It was found that the East Asian Summer Monsoon (EASM) circulation and its transport of moisture leads to a conditional instability, which benefits the local upward motion in summer, and thereby results in an increased amount of high cloud. The deep convective cloud centers were found to coincide well with the northward march of the EASM, while cirrus lagged slightly behind the convection center and coincided well with the outflow and meridional wind divergence of the EASM. Analysis of the radiative heating rates revealed that both the plentiful summer moisture and higher clouds are effective in destabilizing the atmosphere. Moreover, clouds heat the mid-troposphere and the cloud radiative heating is balanced by adiabatic cooling through upward motion, which causes meridional wind by the Sverdrup balance. The cloud heating-forced circulation was observed to coincide well with the EASM circulation, serving as a positive effect on EASM circulation.
Key wordsEast Asian summer monsoon seasonal cycle CloudSat cloud
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