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Title: Entrainment versus Dilution in Tropical Deep Convection

Abstract

In this paper, the distinction between entrainment and dilution is investigated with cloud-resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is presented and calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Dilution by entrainment also increases with increasing updraft velocity but only for sufficiently strong updrafts. Entrainment contributes significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. Finally,more » the results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.« less

Authors:
 [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE; National Science Foundation (NSF); National Oceanic and Atmospheric Administration (NOAA) (United States)
OSTI Identifier:
1438657
Alternate Identifier(s):
OSTI ID: 1406397
Report Number(s):
LLNL-JRNL-737793
Journal ID: ISSN 0022-4928
Grant/Contract Number:  
AC52-07NA27344; AGS-1441916; ATM-0425247; 1433343; NA13OAR4310163; NA12OAR4310077
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the Atmospheric Sciences
Additional Journal Information:
Journal Volume: 74; Journal Issue: 11; Journal ID: ISSN 0022-4928
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES; convection; entrainment; cloud resolving models

Citation Formats

Hannah, Walter M. Entrainment versus Dilution in Tropical Deep Convection. United States: N. p., 2017. Web. doi:10.1175/JAS-D-16-0169.1.
Hannah, Walter M. Entrainment versus Dilution in Tropical Deep Convection. United States. doi:10.1175/JAS-D-16-0169.1.
Hannah, Walter M. Wed . "Entrainment versus Dilution in Tropical Deep Convection". United States. doi:10.1175/JAS-D-16-0169.1.
@article{osti_1438657,
title = {Entrainment versus Dilution in Tropical Deep Convection},
author = {Hannah, Walter M.},
abstractNote = {In this paper, the distinction between entrainment and dilution is investigated with cloud-resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is presented and calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Dilution by entrainment also increases with increasing updraft velocity but only for sufficiently strong updrafts. Entrainment contributes significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. Finally, the results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.},
doi = {10.1175/JAS-D-16-0169.1},
journal = {Journal of the Atmospheric Sciences},
number = 11,
volume = 74,
place = {United States},
year = {Wed Nov 01 00:00:00 EDT 2017},
month = {Wed Nov 01 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on November 1, 2018
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Cited by: 2 works
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