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
Publisher
Language
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
Series/Report No
Department
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
Physical Meteorology program of the National Science Foundation (AGS-1139746)
CIRPAS Twin Otter team
CIRPAS Twin Otter team
Funder
NOAA
Physical Meteorology program of the National Science Foundation (AGS-1139746)
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.