Large-Eddy Simulation of Evaporatively Driven Entrainment in Cloud-Topped Mixed LayersSource: Journal of the Atmospheric Sciences:;2008:;Volume( 065 ):;issue: 005::page 1481DOI: 10.1175/2007JAS2438.1Publisher: American Meteorological Society
Abstract: Cloud-top entrainment instability (CTEI) is a hypothesized positive feedback between cloud-top entrainment and enhanced turbulence associated with buoyancy reversal. A sufficiently strong positive feedback is hypothesized to lead to the destruction of the cloud. Numerous studies have investigated the possible role of CTEI in cloud breakup, with ambiguous results. In this study, CTEI has been extensively investigated using many large-eddy simulations. An idealized experimental design has been used so as not to have any source of turbulence kinetic energy production except for entrainment due to evaporative cooling. A new method has been used to estimate the entrainment rate and to identify the inversion base and top. The results of the experiments do show the hypothesized positive feedback when the Randall?Deardorff CTEI criterion is met. When CTEI takes place in the numerical experiments, entrainment develops spontaneously through buoyancy reversal and, as a result, leads to cloud dissipation. Cloud dissipation within several hours is simulated in the cases with strong instability. A hypothesized dependence of the strength of the evaporatively driven turbulence on the cloud-top liquid water mixing ratio is confirmed. As expected, with a typical stratocumulus liquid water mixing ratio, the evaporatively driven turbulence is weak. Additional simulations with longwave radiation, surface latent heat flux, or both suggest that sufficiently strong radiative cooling can prevent cloud destruction by CTEI. For this reason, CTEI usually does not result in cloud dissipation in realistic cases.
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contributor author | Yamaguchi, Takanobu | |
contributor author | Randall, David A. | |
date accessioned | 2017-06-09T16:18:49Z | |
date available | 2017-06-09T16:18:49Z | |
date copyright | 2008/05/01 | |
date issued | 2008 | |
identifier issn | 0022-4928 | |
identifier other | ams-65556.pdf | |
identifier uri | http://onlinelibrary.yabesh.ir/handle/yetl/4206794 | |
description abstract | Cloud-top entrainment instability (CTEI) is a hypothesized positive feedback between cloud-top entrainment and enhanced turbulence associated with buoyancy reversal. A sufficiently strong positive feedback is hypothesized to lead to the destruction of the cloud. Numerous studies have investigated the possible role of CTEI in cloud breakup, with ambiguous results. In this study, CTEI has been extensively investigated using many large-eddy simulations. An idealized experimental design has been used so as not to have any source of turbulence kinetic energy production except for entrainment due to evaporative cooling. A new method has been used to estimate the entrainment rate and to identify the inversion base and top. The results of the experiments do show the hypothesized positive feedback when the Randall?Deardorff CTEI criterion is met. When CTEI takes place in the numerical experiments, entrainment develops spontaneously through buoyancy reversal and, as a result, leads to cloud dissipation. Cloud dissipation within several hours is simulated in the cases with strong instability. A hypothesized dependence of the strength of the evaporatively driven turbulence on the cloud-top liquid water mixing ratio is confirmed. As expected, with a typical stratocumulus liquid water mixing ratio, the evaporatively driven turbulence is weak. Additional simulations with longwave radiation, surface latent heat flux, or both suggest that sufficiently strong radiative cooling can prevent cloud destruction by CTEI. For this reason, CTEI usually does not result in cloud dissipation in realistic cases. | |
publisher | American Meteorological Society | |
title | Large-Eddy Simulation of Evaporatively Driven Entrainment in Cloud-Topped Mixed Layers | |
type | Journal Paper | |
journal volume | 65 | |
journal issue | 5 | |
journal title | Journal of the Atmospheric Sciences | |
identifier doi | 10.1175/2007JAS2438.1 | |
journal fristpage | 1481 | |
journal lastpage | 1504 | |
tree | Journal of the Atmospheric Sciences:;2008:;Volume( 065 ):;issue: 005 | |
contenttype | Fulltext |