Preprints
https://doi.org/10.5194/acp-2021-937
https://doi.org/10.5194/acp-2021-937

  15 Nov 2021

15 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Influences of Entrainment-Mixing Parameterization on Numerical Simulations of Cumulus and Stratocumulus Clouds

Xiaoqi Xu1,2,4, Chunsong Lu1, Yangang Liu3, Shi Luo1,5, Xin Zhou3, Satoshi Endo3, Lei Zhu1, and Yuan Wang1 Xiaoqi Xu et al.
  • 1Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science & Technology, Nanjing, China
  • 2Nanjing Joint Institute for Atmospheric Sciences, Nanjing, China
  • 3Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, US
  • 4Key Laboratory of Transportation Meteorology, CMA, Nanjing, China
  • 5College of Aviation Meteorology, Civil Aviation Flight University of China, Guanghan, China

Abstract. Different entrainment-mixing processes can occur in clouds; however, a homogeneous mixing mechanism is often implicitly assumed in most commonly used microphysics schemes. Here, we first present a new entrainment-mixing parameterization that uses the grid-mean relative humidity without requiring the relative humidity of the entrained air. Second, the parameterization is implemented in a microphysics scheme in a large eddy simulation model. Third, sensitivity experiments are conducted to compare the new parameterization with the default homogeneous entrainment-mixing parameterization. The results indicate that the new entrainment-mixing parameterization has a larger impact on the number concentration, volume-mean radius, and cloud optical depth in the stratocumulus case than in the cumulus case. This is because inhomogeneous and homogeneous mixing mechanisms dominate in the stratocumulus and cumulus cases, respectively, which is mainly due to the larger turbulence dissipation rate in the cumulus case. Because stratocumulus clouds break up during the dissipation stage to form cumulus clouds, the effects of this new entrainment-mixing parameterization during the stratocumulus dissipation stage are between those during the stratocumulus mature stage and the cumulus case. A large aerosol concentration can enhance the effects of this new entrainment-mixing parameterization by decreasing the cloud droplet size and evaporation time scale. This study sheds new light on the improvement of entrainment-mixing parameterizations in models.

Xiaoqi Xu et al.

Status: open (until 27 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Xiaoqi Xu et al.

Xiaoqi Xu et al.

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Short summary
A new entrainment-mixing parameterization which can be directly implemented in microphysics schemes without requiring the relative humidity of the entrained air is proposed based on the Explicit Mixing Parcel Model. The parameterization is implemented in the two-moment microphysics scheme and exhibits different effects on different types of clouds and even on different stages of stratocumulus clouds, which are affected by turbulent dissipation rate and aerosol concentration.
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