Journal Article

Relationships between Cloud Droplet Spectral Relative Dispersion and Entrainment Rate and Their Impacting Factors

Lu, Chunsong, Zhu, Lei, Luo, Shi, Li, Yaohui, Qiu, Yujun, Li, Junjun, Wu, Junjie, Xu, Xiaoqi, Wang, Yuan, Yang, Xinlin, Gao, Wenhua, Liu, Yangang

2022

Overview

Cloud microphysical properties are significantly affected by entrainment and mixing processes. However, it is unclear how the entrainment rate affects the relative dispersion of cloud droplet size distribution. Previously, the relationship between relative dispersion and entrainment rate was found to be positive or negative. To reconcile the contrasting relationships, the Explicit Mixing Parcel Model is used to determine the underlying mechanisms. When evaporation is dominated by small droplets, and the entrained environmental air is further saturated during mixing, the relationship is negative. However, when the evaporation of big droplets is dominant, the relationship is positive. Whether or not the cloud condensation nuclei are considered in the entrained environmental air is a key factor as condensation on the entrained condensation nuclei is the main source of small droplets. However, if cloud condensation nuclei are not entrained, the relationship is positive. If cloud condensation nuclei are entrained, the relationship is dependent on many other factors. High values of vertical velocity, relative humidity of environmental air, and liquid water content, and low values of droplet number concentration, are more likely to cause the negative relationship since new saturation is easier to achieve by evaporation of small droplets. Further, the signs of the relationship are not strongly affected by the turbulence dissipation rate, but the higher dissipation rate causes the positive relationship to be more significant for a larger entrainment rate. A conceptual model is proposed to reconcile the contrasting relationships. This work enhances the understanding of relative dispersion and lays a foundation for the quantification of entrainment-mixing mechanisms.

• Publisher: Science Press,Springer Nature B.V,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)/Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,Nanjing University of Information Science&Technology,Nanjing 210044,China%Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)/Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,Nanjing University of Information Science&Technology,Nanjing 210044,China%Environmental and Climate Sciences Department,Brookhaven National Laboratory,Upton,New York 11973,US%College of Aviation Meteorology,Civil Aviation Flight University of China,Guanghan 618307,China%State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences,Beijing 100081,China%Nanjing Joint Institute for Atmospheric Sciences,Nanjing 210019,China%Collaborative Innovation Center for Western Ecological Safety,Lanzhou University,Lanzhou 730000,China,College of Aviation Meteorology,Civil Aviation Flight University of China,Guanghan 618307,China,Springer
• Subject: Aerosols / Air / Air entrainment / Atmospheric Sciences / Aviation / Cloud condensation nuclei / Cloud droplet size / Cloud droplet size distribution / Cloud droplets / Cloud microphysics / Clouds / Condensation / Condensation nuclei / Dispersion / Dissipation / Droplets / Earth and Environmental Science / Earth Sciences / Entrainment / entrainment rate / ENVIRONMENTAL SCIENCES / Evaporation / Geophysics/Geodesy / Humidity / Liquid water content / Meteorology / Mixing / mixing and evaporation / Mixing processes / Moisture content / Nucleus / Original Paper / Physics / Precipitation / Radiation / relative dispersion if cloud droplet size distribution / Relative humidity / Size distribution / their interactions / Turbulence / Velocity / Vertical velocities / Water / Water content