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| Titel |
Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06 |
| VerfasserIn |
A. H. Berner, C. S. Bretherton, R. Wood |
| 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 ; 11, no. 20 ; Nr. 11, no. 20 (2011-10-24), S.10525-10540 |
| Datensatznummer |
250010141
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| Publikation (Nr.) |
 copernicus.org/acp-11-10525-2011.pdf |
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| Zusammenfassung |
Large-eddy simulations of a pocket of open cells (POC) based on VOCALS
Regional Experiment (REx) NSF C-130 Research Flight 06 are analyzed and compared with
aircraft observations. A doubly-periodic domain 192 km × 24 km with
125 m horizontal and 5 m vertical grid spacing near the capping
inversion is used. The POC is realized in the model as a fixed 96 km wide
region of reduced cloud droplet number concentration (Nc) based on
observed values; initialization and forcing are otherwise uniform across the
domain. The model reproduces aircraft-observed differences in boundary-layer
structure and precipitation organization between a well-mixed overcast region
and a decoupled POC with open-cell precipitating cumuli, although the
simulated cloud cover is too large in the POC. A sensitivity study in which
Nc is allowed to advect following the turbulent flow gives nearly
identical results over the 16 h length of the simulation (which starts at
night and goes into the next afternoon).
The simulated entrainment rate is nearly a factor of two smaller in the less
turbulent POC than in the more turbulent overcast region. However, the
inversion rises at a nearly uniform rate across the domain because powerful
buoyancy restoring forces counteract horizontal inversion height gradients. A
secondary circulation develops in the model that diverts subsiding free-tropospheric air
away from the POC into the surrounding overcast region, counterbalancing the
weaker entrainment in the POC with locally weaker subsidence. |
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