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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Dependence of mixed-layer entrainment on shear stress and velocity jump
James W. Deardorff,G. E. Willis +1 more
TL;DR: In this article, the mixed-layer growth rate was found to depend on both the surface friction velocity and the interfacial velocity jump in a multiplicative sense, with the velocity-jump dependence being the stronger.
Journal ArticleDOI
Erosion of a stable density gradient by sedimentation-driven convection
TL;DR: In this paper, it has been shown that turbidity currents provide an indirect mechanism for eroding this stratification, where light ambient fluid that has been mixed by cyclones with dense suspended sediment is transported to greater depths, where it convectively erodes the gradient as the sediment settles.
Journal ArticleDOI
Stably Stratified Interfacial-Layer Turbulence from Large-Eddy Simulation
Martin J. Otte,John C. Wyngaard +1 more
TL;DR: In this paper, a series of 26 high-resolution large eddy simulation runs ranging from neutral, inversion-capped to free-convection cases are used to study interfacial layer turbulence.
Journal ArticleDOI
Ground-level concentrations due to fumigation into an entraining mixed layer
James W. Deardorff,G.E. Willis +1 more
TL;DR: In this article, the authors show that the near surface concentration of a fumigating ribbon is independent of both the initial lateral and vertical dimensions of the fuming plume, and that the entrainment rate depends on averaging time and the angle between the wind velocity inside the mixed layer and just above.
Journal ArticleDOI
Study of the planetary boundary layer by microwave radiometer, elastic lidar and Doppler lidar estimations in Southern Iberian Peninsula
Gregori de Arruda Moreira,Juan Luis Guerrero-Rascado,Juan Antonio Bravo-Aranda,Jose Antonio Benavent-Oltra,Pablo Ortiz-Amezcua,Roberto Román,Roberto Román,Andrés Esteban Bedoya-Velásquez,Andrés Esteban Bedoya-Velásquez,Eduardo Landulfo,Lucas Alados-Arboledas +10 more
TL;DR: In this article, an extended Kalman filter method is applied to data obtained by the elastic lidar while the vertical wind speed variance method was applied to the Doppler lidar, and the results show a good agreement among these retrievals based on active remote sensing in most of the cases, although some discrepancies appear in instances of intense PBL changes (either growth and/or decrease).
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.
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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.
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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 *.
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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.