Abstract:
Using cloud profile radar (CPR/CloudSat) data from 2007 to 2009, the horizontal distributions of non-precipitating warm clouds over global oceans were examined and the vertical variation characteristics of LWC (liquid water content) were analyzed for four major warm cloud types, i.e., cumulus (Cu), stratus (St), stratocumulus (Sc) and altocumulus (Ac). It was found that among all oceanic non-precipitating warm clouds, the proportion of each type is stratocumulus (76.46%), stratus (12.48%), cumulus (7.45%) and altocumulus (3.61%). Stratocumulus plays a dominant role in the total coverage area of non-precipitating warm clouds over oceans. After the global normalization of the sample volume, there are also large differences in the spatial distribution patterns among the four types. Stratocumulus and stratus are mainly concentrated in coastal waters near the west of North and South American continents, while cumulus and altocumulus clouds are widely distributed on the Pacific Ocean, Atlantic Ocean and Indian Ocean, and high occurrences generally appear in the central part of each ocean. In spite of distinct formation regimes and morphologies, the vertical structures of LWC show similar patterns among the four types. From the cloud bottom up to cloud top, LWC was found to increase first and then decrease. The approximately linearly increasing structure in the lower and middle part of the cloud column reflects the quasi-adiabatic growth characteristics of LWC. The upward decreasing structure near the upper part and near cloud top clearly reflects that cloud top is generally strongly affected by the intrusion of overhead dry air. The resulting evaporation of cloud water attenuates heavily downward from the cloud top. The LWC vertical structure was found to be affected by cloud top height and cloud thickness. As cloud thickness increases, the upward increasing part becomes thicker, while the upward decreasing part becomes thinner. Clouds with the same thickness but different cloud top heights also have different LWC structures. This indicates that for a particular type of the clouds, there are differences in the LWC structures corresponding to different periods during the cloud’s generation and development process.
