Journal ArticleDOI
Laboratory studies of the entrainment zone of a convectively mixed layer
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In this article, the entrainment zone of simulated atmospheric mixed layers is investigated from measurements of horizontally averaged temperature and buoyancy flux, and from visual observations of penetrating thermals using a spread laser beam.Abstract:
In laboratory experiments of simulated atmospheric mixed layers the entrainment zone is investigated from measurements of horizontally averaged temperature and buoyancy flux, and from visual observations of penetrating thermals using a spread laser beam. The region of negative buoyancy flux of entrainment is found to be confined between the outermost height reached by the few most vigorous penetrating parcels, and by the lesser height where mixed-layer fluid occupies, usually, some 90 to 95% of the total area. The height of most negative buoyancy flux of entrainment is found to agree roughly with the level at which mixed-layer fluid occupies half the area.The thickness of the entrainment zone, relative to the depth of the well-mixed layer just beneath, is found to be quite substantial (0·2 to 0·4), and apparently decreases only asymptotically with increasing ‘overall’ Richardson number, Ri*. The thickness is not well predicted by parcel theory.Extensive detrainment is found to occur within the entrainment zone, and adds to the difficulty in defining the position of the local interface between mixed-layer fluid and unmodified fluid.For typical Ri* values occurring in the atmosphere, the dimensionless entrainment rate is found to be given satisfactorily by 0·25(Ri*)−1, although an dependence cannot be ruled out by the present data. Entrainment into a neutral layer in the absence of a capping inversion is found to proceed at the expected rate.read more
Citations
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Journal ArticleDOI
Dependence of mixed-layer entrainment on shear stress and velocity jump
James W. Deardorff,G. E. Willis +1 more
TL;DR: In this article, it was shown that the entrainment rate is a function of both the overall Richardson number, R T, and the inverse Froude number (R v ), and that R v is a variable that is influenced by sidewall friction, time after onset of the surface stress, or other factors.
Journal ArticleDOI
Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer
E. Blay-Carreras,David Pino,J. Vilà-Guerau de Arellano,A. van de Boer,O. de Coster,Clara Darbieu,Oscar Hartogensis,Fabienne Lohou,Marie Lothon,H.P. Pietersen +9 more
TL;DR: In this article, the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer was investigated. But the authors focused on the role of the residual layers during the late afternoon and sunset Turbulence campaign.
Journal ArticleDOI
On plume rise within a convective boundary layer
G.E. Willis,James W. Deardorff +1 more
TL;DR: In this paper, the authors measured the plume buoyancy from a model stack within a laboratory convectively mixed layer and determined the centerline height of plume envelopes and centerline heights.
Journal ArticleDOI
Including Radiative Effects in an Entrainment Rate Formula for Buoyancy-Driven PBLs
TL;DR: In this article, the effect of longwave radiative cooling at the planetary boundary layer (PBL) top in determining the entrainment rate was examined in a large eddy simulation.
Journal ArticleDOI
Direct numerical simulation of free convection over a heated plate
TL;DR: In this article, a quasi-steady inner layer and a self-preserving outer layer are clearly distinguished, with an overlap region between them of constant turbulent buoyancy flux.
References
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Journal ArticleDOI
Three-dimensional numerical study of the height and mean structure of a heated planetary boundary layer
TL;DR: In this article, a three-dimensional model using 64000 grid points within a volume 5 km on a side and 2 km deep was used to study the heated boundary layer for DAY 33 of the Wangara data of southeast Australia.
Journal ArticleDOI
On the penetration of a turbulent layer into stratified fluid
H. Kato,Owen M. Phillips +1 more
TL;DR: In this article, a constant stress is applied to the surface of an initially quiescent tank of fluid with a uniform density gradient, and the development of the turbulent layer by entrainment of the underlying fluid is described.
Journal ArticleDOI
Non-precipitating cumulus convection and its parameterization
TL;DR: In this paper, the authors discussed the thermodynamic transport of heat, liquid water and (briefly) water vapour by non-precipitating cumulus convection.
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A Laboratory Model of the Unstable Planetary Boundary Layer
G. E. Willis,James W. Deardorff +1 more
TL;DR: In this paper, a laboratory model of the unstable planetary boundary layer is presented and compared with atmospheric observations, showing that good agreement exists between the model measurements and the atmospheric observations when the variables are appropriately scaled with the depth of the mixed layer zi, and the convective velocity and temperature scales w* and T *.
Journal ArticleDOI
The influence of molecular diffusivity on turbulent entrainment across a density interface
TL;DR: In this article, the rate of mixing across a density interface between two layers of liquid has been measured in a laboratory experiment which allows a direct comparison between heat and salinity transports over the same range of density differences.