Publication:
Observational estimates of detrainment and entrainment in non-precipitating shallow cumulus

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Authors
Norgren, M.S.
Small, J.D.
Jonsson, H.H.
Chuang, P.Y.
Subjects
Advisors
Date of Issue
2016
Date
2016
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Abstract
Vertical transport associated with cumulus clouds is important to the redistribution of gases, particles, and energy, with subsequent consequences for many aspects of the climate system. Previous studies have suggested that detrainment from clouds can be comparable to the updraft mass flux, and thus represents an important contribution to vertical transport. In this study, we describe a new method to deduce the amounts of gross detrainment and entrainment experienced by non-precipitating cumulus clouds using aircraft observations. The method utilizes equations for three conserved variables: cloud mass, total water, and moist static energy. Optimizing these three equations leads to estimates of the mass fractions of adiabatic mixed-layer air, entrained air and detrained air that the sampled cloud has experienced. The method is applied to six flights of the CIRPAS Twin Otter during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) which took place in the Houston, Texas region during the summer of 2006 during which 176 small, non-precipitating cumuli were sampled. Using our novel method, we find that, on average, these clouds were comprised of 30 to 70% mixed-layer air, with entrained air comprising most of the remainder. The mass fraction of detrained air was usually very small, less than 2 %, although values larger than 10% were found in 15% of clouds. Entrained and detrained air mass fractions both increased with altitude, consistent with some previous observational studies. The largest detrainment events were almost all associated with air that was at their level of neutral buoyancy, which has been hypothesized in previous modeling studies. This new method could be readily used with data from other previous aircraft campaigns to expand our understanding of detrainment for a variety of cloud systems.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.5194/acp-16-21-2016
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Department
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Naval Postgraduate School (U.S.)
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NPS Report Number
Sponsors
Physical Meteorology program of the National Science Foundation (AGS-1139746)
CIRPAS Twin Otter team
Funder
NOAA
Physical Meteorology program of the National Science Foundation (AGS-1139746)
Format
13 p.
Citation
Atmos. Chem. Phys., 16, 21–33, 2016
Distribution Statement
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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