Conditions for super-adiabatic droplet growth after entrainment mixing
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 »
- Authors:
-
[1]
; [1]
; [2]
- Michigan Technological Univ., Houghton, MI (United States)
- Peking Univ., Beijing (China)
- Publication Date:
- Grant/Contract Number:
- SC0011690
- Type:
- 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
- Research Org:
- Michigan Technological Univ., Houghton, MI (United States)
- Sponsoring Org:
- USDOE Office of Science (SC)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
- OSTI Identifier:
- 1275972
- Alternate Identifier(s):
- OSTI ID: 1360122
Yang, Fan, Shaw, Raymond, and Xue, Huiwen. Conditions for super-adiabatic droplet growth after entrainment mixing. United States: N. p.,
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. 2016.
"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 = {2016},
month = {7}
}