Abstract:
Using the CloudSat/CALIPSO data products during the period of September 2006－August 2009, seasonal variations of cloud properties （including occurrence frequency, vertical location, physical thickness, distance between cloud layers, and vertical distribution of radar reflectivity) are contrasted among four regions: East Asian Monsoon Region（EAMR), Indian Monsoon Region（IMR), the Western North Pacific Monsoon Region（WNPMR), and the Tibetan Plateau Region（TPR). The geographical distribution of low-level clouds over the Asian monsoon regions and its correlation with atmospheric stability of the lower troposphere（LTS) are also analyzed. The major findings are as follows:（1) During the period, the total cloud amounts are 69% （EAMR), 72%（IMR), 83%（WNPMR), and 69%（TPR), respectively, to which single-layer clouds contribute 56%（IMR and WNPMR) to 77%（TPR). The multi-layer clouds are mostly double-layered or triple-layered（fractions≥95%). In the IMR, the total cloud amount in summer （greater than 90%) is significantly larger than in winter（about 50%); the total cloud amounts are larger during spring and summer（>90%) than autumn and winter（about 50%) in the EAMR and TPR; the seasonal variation is negligible over the WNPMR.(2) Clouds located above 10 km containing small ice crystals prevail in the tropical monsoon regions （IMR and WNPMR) all the year round. Marine boundary layer clouds are common during each season in the WNPMR, in contrast to the IMR where low-level clouds occur mainly during summer. The EAMR clouds are located mostly below 10 km from autumn to spring. Although more clouds are present in the upper troposphere during summer than other seasons over the EAMR, their occurrences and vertical locations are lower than those in the IMR and WNPMR（cloud amount of 60%－70% from 12 to 16 km heights). The TPR clouds are mostly located in the height range of 4－11 km, with cloud particles at the same height covering a wide range of size.(3) The geographical distributions of low-level clouds in the Asian monsoon region are similar between spring and autumn, and significantly distinct between summer and winter. Low-level clouds are the most abundant during winter（45%－70%), located mainly in the western North Pacific, southern Chinese mainland and the oceans to its east, and the regions around Japan. The low-level cloud amount is correlated with LTS quite well except for winter.(4) The cloud layers are geometrically thin in the four regions, with 30%－36% being thinner than 1 km. Moreover, the vertical distance between two consecutive layers in multilayered clouds with values less than 1 km accounts for about 10%. Both suggest a need to improve the vertical resolution of current general circulation models.
