Contrasting Scale Dependence of Entrainment-Mixing Mechanisms in Stratocumulus Clouds

Journal Article · Sat May 16 00:00:00 EDT 2020 · Geophysical Research Letters

DOI:https://doi.org/10.1029/2020GL086970· OSTI ID:1638032

Gao, Sinan ^[1]; Lu, Chunsong ^[1]; Liu, Yangang ^[2]; Mei, Fan  ^[3]; Wang, Jian ^[2]; Zhu, Lei ^[1]; Yan, Shuqi ^[4]

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1. Nanjing University of Science and Technology
2. Brookhaven National Laboratory
3. BATTELLE (PACIFIC NW LAB)
4. Nanjing University

The apparent turbulent entrainment-mixing mechanism between clouds and surrounding air is scale-dependent; however, such scale dependence has been rarely studied, hindering development of scale-aware entrainment-mixing parameterizations. Here we extend our previous study on cumulus clouds to investigate scale dependence of entrainment-mixing processes in stratocumulus clouds during ACE-ENA and RACORO. In contrast to previous studies, two opposite scale dependencies are found: entrainment-mixing can become more homogeneous or more inhomogeneous with increasing averaging scales, which is quantified by the difference between homogeneous mixing degree at the 100 m and 10 m resolutions. A new heuristic model and two new quantities are introduced. The observations and model show that microphysical properties near and far away from droplet-free air and relative humidity of entrained air determine both the sign and strength of scale dependence, while droplet-free air fraction only affects the strength. The results shed new light on developing scale-aware parameterizations of entrainment-mixing mechanisms.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1638032
• Report Number(s): PNNL-SA-153067
• Journal Information: Geophysical Research Letters, Vol. 47, Issue 9
• Country of Publication: United States
• Language: English