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| Titel |
Observational constraints on entrainment and the entrainment interface layer in stratocumulus |
| VerfasserIn |
J. K. Carman, D. L. Rossiter, D. Khelif, H. H. Jonsson, I. C. Faloona, P. Y. Chuang |
| 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 ; 12, no. 22 ; Nr. 12, no. 22 (2012-11-23), S.11135-11152 |
| Datensatznummer |
250011620
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| Publikation (Nr.) |
 copernicus.org/acp-12-11135-2012.pdf |
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| Zusammenfassung |
| Aircraft sampling of the stratocumulus-topped boundary layer (STBL) during
the Physics of Stratocumulus Top (POST) experiment was primarily achieved
using sawtooth flight patterns, during which the atmospheric layer 100 m
above and below cloud top was sampled at a frequency of once every 2 min.
The large data set that resulted from each of the 16 flights document the
complex structure and variability of this interfacial region in a variety of
conditions. In this study, we first describe some properties of the
entrainment interface layer (EIL), where strong gradients in turbulent
kinetic energy (TKE), potential temperature and moisture can be found. We
find that defining the EIL by the first two properties tends to yield similar
results, but that moisture can be a misleading tracer of the EIL. These
results are consistent with studies using large-eddy simulations. We next
utilize the POST data to shed light on and constrain processes relevant to
entrainment, a key process in the evolution of the STBL that to-date is not
well-represented even by high resolution models. We define "entrainment
efficiency" as the ratio of the TKE consumed by entrainment to that
generated within the STBL (primarily by cloud-top cooling). We find values
for the entrainment efficiency that vary by 1.5 orders of magnitude, which is
even greater than the one order magnitude that previous modeling results have
suggested. Our analysis also demonstrates that the entrainment efficiency
depends on the strength of the stratification of the EIL, but not on the TKE
in the cloud top region. The relationships between entrainment efficiency and
other STBL parameters serve as novel observational contraints for simulations
of entrainment in such systems. |
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