Journal ArticleDOI
Laboratory studies of the entrainment zone of a convectively mixed layer
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TLDR
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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An analytical study of cumulus onset
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Convectively driven exchange flow in a stratified sill-enclosed basin
T.D. Finnigan,Gregory Ivey +1 more
TL;DR: In this article, the authors investigate the processes governing steady convectively driven circulation in a basin that communicates with a large external reservoir over a shallow sill and show that inertia, buoyancy and friction may each contribute significantly to the balance.
Dissertation
Resolving the atmospheric sulphur budget over the Elandsfontein area of the Mpumalanga Highveld
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Revisiting entrainment relationships for shear-free and sheared convective boundary layers through large-eddy simulations
TL;DR: In this article, the entrainment relationship is systematically evaluated from large-eddy simulations (LESs) of shear-free and sheared CBLs under a broad variety of atmospheric conditions.
Journal ArticleDOI
Molecular‐diffusive effects in penetrative convection
H. J.S. Fernando,Leigh J. Little +1 more
TL;DR: In this article, the influence of molecular diffusion on turbulent entrainment during penetrative convection was investigated, and the entraining coefficient E was determined as a function of the Richardson number Ri and Peclet number Pe.
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.
Journal ArticleDOI
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.