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Title: Conditions for super-adiabatic droplet growth after entrainment mixing

Journal Article · · Atmospheric Chemistry and Physics (Online)
 [1];  [1];  [2]
  1. Michigan Technological Univ., Houghton, MI (United States)
  2. Peking Univ., Beijing (China)
+ Show Author Affiliations

Cloud droplet response to entrainment and mixing between a cloud and its environment is considered, accounting for subsequent droplet growth during adiabatic ascent following a mixing event. The vertical profile for liquid water mixing ratio after a mixing event is derived analytically, allowing the reduction to be predicted from the mixing fraction and from the temperature and humidity for both the cloud and environment. It is derived for the limit of homogeneous mixing. The expression leads to a critical height above the mixing level: at the critical height the cloud droplet radius is the same for both mixed and unmixed parcels, and the critical height is independent of the updraft velocity and mixing fraction. Cloud droplets in a mixed parcel are larger than in an unmixed parcel above the critical height, which we refer to as the “super-adiabatic” growth region. Analytical results are confirmed with a bin microphysics cloud model. Using the model, we explore the effects of updraft velocity, aerosol source in the environmental air, and polydisperse cloud droplets. Results show that the mixed parcel is more likely to reach the super-adiabatic growth region when the environmental air is humid and clean. It is also confirmed that the analytical predictions are matched by the volume-mean cloud droplet radius for polydisperse size distributions. Lastly, these findings have implications for the origin of large cloud droplets that may contribute to onset of collision–coalescence in warm clouds.

Research Organization:
Michigan Technological Univ., Houghton, MI (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
SC0011690
OSTI ID:
1275972
Alternate ID(s):
OSTI ID: 1360122
Journal Information:
Atmospheric Chemistry and Physics (Online), Vol. 16, Issue 14; ISSN 1680-7324
Publisher:
European Geosciences UnionCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 22 works
Citation information provided by
Web of Science

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Cited By (3)

Observational Relationship Between Entrainment Rate and Environmental Relative Humidity and Implications for Convection Parameterization journal December 2018
Theoretical analysis of mixing in liquid clouds – Part IV: DSD evolution and mixing diagrams journal January 2018
Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation journal January 2018

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