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| Titel |
Direct entrainment and detrainment rate distributions of individual shallow cumulus clouds in an LES |
| VerfasserIn |
J. T. Dawe, P. H. Austin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 15 ; Nr. 13, no. 15 (2013-08-13), S.7795-7811 |
| Datensatznummer |
250085624
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| Publikation (Nr.) |
 copernicus.org/acp-13-7795-2013.pdf |
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| Zusammenfassung |
| Probability distribution functions of shallow cumulus cloud core
entrainment and detrainment rates are calculated using 4362
individual cumulus clouds isolated from LES (large eddy simulation) using a cloud tracking
algorithm. Calculation of the mutual information between fractional
entrainment/detrainment and a variety of mean cloud core properties
suggests that fractional entrainment rate is best predicted by the
mean cloud buoyancy B and the environmental buoyancy lapse rate
dθρ/dz
at that level, while
fractional detrainment is best predicted by the mean vertical
velocity w and the critical mixing fraction χc. Fractional
entrainment and detrainment rates are relatively insensitive to
cloud core horizontal area, and the perimeter of horizontal
cloud core sections display an a0.73 dependence. This implies
that cloud core mass entrainment flux E is proportional to cloud
core cross-sectional area instead of cloud core surface area, as is
generally assumed. Empirical best-fit relations for ε(B,
dθρ/dz and δ(w,
χc) are found for both individual shallow cumulus clouds and
cloud ensembles. It is found that clouds with high buoyancy in
strong stratification experience low entrainment rates, while clouds
with high vertical velocities and critical mixing fractions
experience low detrainment rates. |
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