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

Abstract

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 analyticalmore » 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.« less

Authors:
 [1];  [1];  [2]
  1. Michigan Technological Univ., Houghton, MI (United States)
  2. Peking Univ., Beijing (China)
Publication Date:
Research Org.:
Michigan Technological Univ., Houghton, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1275972
Alternate Identifier(s):
OSTI ID: 1360122
Grant/Contract Number:  
SC0011690
Resource Type:
Journal Article: Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 16; Journal Issue: 14; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Yang, Fan, Shaw, Raymond, and Xue, Huiwen. Conditions for super-adiabatic droplet growth after entrainment mixing. United States: N. p., 2016. Web. doi:10.5194/acp-16-9421-2016.
Yang, Fan, Shaw, Raymond, & Xue, Huiwen. Conditions for super-adiabatic droplet growth after entrainment mixing. United States. doi:10.5194/acp-16-9421-2016.
Yang, Fan, Shaw, Raymond, and Xue, Huiwen. Fri . "Conditions for super-adiabatic droplet growth after entrainment mixing". United States. doi:10.5194/acp-16-9421-2016.
@article{osti_1275972,
title = {Conditions for super-adiabatic droplet growth after entrainment mixing},
author = {Yang, Fan and Shaw, Raymond and Xue, Huiwen},
abstractNote = {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.},
doi = {10.5194/acp-16-9421-2016},
journal = {Atmospheric Chemistry and Physics (Online)},
number = 14,
volume = 16,
place = {United States},
year = {Fri Jul 29 00:00:00 EDT 2016},
month = {Fri Jul 29 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.5194/acp-16-9421-2016

Citation Metrics:
Cited by: 4 works
Citation information provided by
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