Parameterizations of Entrainment‐Mixing Mechanisms and Their Effects on Cloud Droplet Spectral Width Based on Numerical Simulations. Issue 22 (18th November 2020)

• Record Type: Journal Article
• Authors: Luo, Shi; Lu, Chunsong; Liu, Yangang; Bian, Jianchun; Gao, Wenhua; Li, Junjun; Xu, Xiaoqi; Gao, Sinan; Yang, Suying; Guo, Xiaohao
• Is Part Of: Journal of geophysical research. Volume 125:Issue 22(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-11-18
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD032972
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Entrainment‐mixing mechanisms significantly affect cloud droplet number concentration, radius, and spectral shape. Quantitative examination of entrainment‐mixing effects on cloud droplet spectral width is lacking. This study examines the effects of entrainment‐mixing processes on cloud microphysics by 12, 218 different setups, each simulated 10 times using the Explicit Mixing Parcel Model (EMPM) driven by the observational data from the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX‐III) campaign. Parameterizations of entrainment‐mixing mechanisms are developed by relating homogeneous mixing degree to transition scale number that depends on the dissipation rate and droplet evaporation time scale. The correlation between relative dispersion of cloud droplet size distribution and homogeneous mixing degree changes from negative to positive with the decreasing homogeneous mixing degree. The different relationships are closely related to the competition between complete and partial droplet evaporation and the number concentration of small droplets, which are quantitatively described by two newly introduced dimensionless numbers. The competition is significantly affected by relative humidity and mixing fraction of entrained air as well as turbulence dissipation rate, but not much by cloud droplet number concentration. Especially, when relative humidity and dissipation rate are high, there is only a negative correlation. This study sheds new light on generalizing the homogeneous/inhomogeneous concept by considering relative dispersion and also provides parameterizations of entrainment‐mixing processes and relative dispersion for atmospheric models. Key Points: Turbulent entrainment‐mixing mechanisms are examined and parameterized Relationship between cloud droplet spectral width and entrainment‐mixing mechanisms is quantified Factors and physical mechanisms are dissected by two newly defined quantities measuring the competition of complete/partial evaporation