Evolutionary Pattern of Marine Stratocumulus Clouds Inferred from Satellite Snapshot Measurements

Microphysical characteristics of stratocumulus clouds and their associated warm-rain processes have been heavily investigated by using satellite observations, particularly from cloud radar and lidar instruments aboard low-orbiting satellites. Owing to the discrete-snapshot nature of such measurements, numerous statistical relationships among microphysical properties have been established, yet the processes of stratocumulus evolution cannot be reasonably delineated, with the temporal evolution of cloud microphysics remaining unclear. Based on cloud geometric thickness and cloud-top height derived from the CPR (Cloud Profiling Radar) aboard CloudSat, this study proposes a method to classify pixel-level samples of stratocumulus clouds into five distinct groups, each corresponding to a specific stage in the cloud lifecycle. Given these five stages as components, an evolutionary pattern of stratocumulus clouds with respect to precipitation onset is constructed. It is found that three pathways of evolution exist from formation to dissipation. Precipitation is nearly absent in two of the pathways, which contain only two or three component stages and are characterized by modest temporal variation of geometric thickness and microphysical properties. The other pathway contains all the five stages and produces considerable precipitation in its mature phase, which attains the largest cloud thickness. In this pathway, the vertical structure of the cloud droplet effective radius does not vary in phase with that of the cloud droplet number concentration. The vertical structure of liquid water content generally follows that of the cloud droplet effective radius. These two parameters both turn to increase monotonically downward during dissipation, where stratocumulus clouds eventually become stable as a non-precipitating thin form.