Microphysical imprint of entrainment in warm cumulus
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Authors
Small, Jennifer D.
Chuang, Patrick Y.
Jonsson, Haflidi H.
Subjects
inhomogeneous mixing
homogeneous mixing
GoMACCS
phase-Doppler interferometer
cloud microphysics
homogeneous mixing
GoMACCS
phase-Doppler interferometer
cloud microphysics
Advisors
Date of Issue
2013
Date
Publisher
Language
Abstract
We analyse the cloud microphysical response to entrainment mixing in warm cumulus clouds observed from
the CIRPAS Twin Otter during the GoMACCS field campaign near Houston, Texas, in summer 2006. Cloud
drop size distributions and cloud liquid water contents from the Artium Flight phase-Doppler interferometer
in conjunction with meteorological observations are used to investigate the degree to which inhomogeneous
versus homogeneous mixing is preferred as a function of height above cloud base, distance from cloud edge and
aerosol concentration. Using four complete days of data with 101 cloud penetrations (minimum 300m in
length), we find that inhomogeneous mixing primarily explains liquid water variability in these clouds.
Furthermore, we show that there is a tendency for mixing to be more homogeneous towards the cloud top,
which we attribute to the combination of increased turbulent kinetic energy and cloud drop size with altitude
which together cause the Damko¨ hler number to increase by a factor of between 10 and 30 from cloud base to
cloud top. We also find that cloud edges appear to be air from cloud centres that have been diluted solely
through inhomogeneous mixing. Theory predicts the potential for aerosol to affect mixing type via changes in
drop size over the range of aerosol concentrations experienced (moderately polluted rural sites to highly
polluted urban sites). However, the observations, while consistent with this hypothesis, do not show a
statistically significant effect of aerosol on mixing type.
Type
Article
Description
The article of record as published may be located at http://dx.doi.org/10.3402/tellusb.v65i0.19922
Series/Report No
Department
Meteorology
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Citation
Tellus, Series B, 2013, 65, 19922, http://dx.doi.org/10.3402/tellusb.v65i0.19922
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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.