A numerical study of the nocturnal atmospheric boundary layer

A one-dimensional numerical model based on the equations of mean motion and turbulent kinetic energy (TKE), with Delage's (1974) mixing-length parameterization has been used to simulate the mean and turbulent structure ofthe evolving stably stratified nocturnal boundary layer (NBL). The model also includes a predictive equation for the surface temperature and longwave radiational cooling effects.In the absence of advective and gravity wave effects, it is found that the model-simulated structure, after a few hours of evolution, could be ordered fairly well by a similarity scaling (u *0, 0*0, L,, and h) based on surface fluxes and the NBL height. Simple expressions are suggested to describe the normalized profiles of momentum and heat fluxes, TKE, eddy-viscosity and energy dissipation. A good ordering of the same variables is also achieved by a local scaling (U * , 0*, and L) based on the height-dependent local fluxes. The normalized TKE, eddy viscosity and energy dissipation are unique functions of z/L and approach constant values as z/L + co, where L is the local Monin-Obukhov length. These constants are close to the values predicted for the surface layer as z/L + co, thus suggesting that the Monin-Obukhov similarity theory can be extended to the whole NBL, by using the local (height-dependent) scales in place of surface-layer scales. The observed NBL structure has been shown to follow local similarity (Nieuwstadt, 1984).

Section: Mean Profilesmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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A numerical model study of the structure and similarity scaling of the nocturnal boundary layer (NBL)

Lacser

Arya

1986

“…The Therry and Lacarrere (1983) diffusion length scale that is based on the height above the terrain and a vertically integrated turbulence kinetic energy profile was used in the present model to determine the vertical eddy-exchange coefficient, K,. Therry and Lacarrere's length scale is similar in principle to the Delage (1974) method, which was shown by Lacser and Arya (1986) to be superior to other methods tested in a one-dimensional stably stratified model. The length scales computed from the hydrostatic simulation (not shown) have contours that are nearly parallel to the terrain.…”

Section: Simulationmentioning

confidence: 92%

Application of a quasi-nonhydrostatic parameterization for numerically modeling neutral flow over an isolated hill

Fast

Takle

1988

A parameterization of the nonhydrostatic pressure was modified and adapted to a nonlinear numerical model of the neutral atmospheric boundary layer. A hydrostatic model and the quasinonhydrostatic version were used to simulate neutral flow over a symmetrical hill of uniform roughness. Mean-flow quantities and some turbulence characteristics of the flow from both models are presented. These results were compared with observations, analytic theory, and other numerical models.The quasi-nonhydrostatic method produced qualitative features commonly observed in such flows that the hydrostatic model could not simulate. For instance, the observed velocity reduction at the hill base and the speedup at the summit both were simulated by the quasi-nonhydrostatic model. However, computation of vertical velocities from the incompressible continuity equation is inadequate above regions of recirculation and presents a limitation to the method.

“…The Wangara data set has been used widely to test model simulations of the outer layer (Deardorff, 1974a(Deardorff, , 1974bClarke, 1974;Orlanski et al 1974;Delage, 1974;Yamada and Mellor, 1975;Pielke and Mahrer, 1975;Wippermann, 1975;Wyngaard, 1975;Schemm and Lipps, 1976;Misra, 1977;Yu, 1977;Burk, 1977;Andre et al, 1978;Bodin, 1979). Several factors, in addition to the high quality of the data, have made the Wangara data very popular among modelers.…”

Section: The~uterlayermentioning

confidence: 99%

The impact of the Wangara experiment

Hess

Hicks

Yamada

1981

Our understanding of the structure and dynamics of the atmospheric boundary layer (ABL) is often limited by a lack of experimental data. The voluminous amount of high quality data obtained from the Wangara Experiment (Clarke et al., 1971) has contributed greatly to meeting a long-standing need, particularly for data describing the ABL in middle latitudes over land.In the surface layer the measurements provided the basis for determination of the stability dependence of the dimensionless gradients d,+, and dH arising out of Monin-Obukhov similarity theory (Hicks, 1976). In the outer layer where the choice of scaling parameters is not unique, the data have been used to determine the stability dependence of the similarity functions A, B, and C, and the most appropriate choices of scaling parameters (e.g., Yamada, 1976). In addition, the experimental data give determinations of some of the fundamental constants of turbulent flow in the ABL, such as the Von Kdrmin constant k = 0.40-0.41 (Hicks, 1969), and the neutral barotropic ABL similarity constants A,, = 1.1 and & = 4.3 (Clarke and Hess, 1974), where the subscript 0 indicates that the surface geostrophic wind was used as reference.Perhaps the greatest impact of the Wangara Experiment has been to provide a data bank which could be used to test numerical simulations of the ABL. This has been useful not only for the newly developed higher-order closure models, but also for one-layer integral models predicting the height of the mixed layer and the height of the nocturnal surface inversion layer.Lastly, the Wangara Experiment has pointed out some of the limitations and difficulties of obtaining accurate measurements of thermal winds, vertical velocity, acceleration terms, and representative spatially averaged fluxes. Microscale turbulence measurements outside the surface layer were not included in the Wangara Experiment and further experiments are needed to determine these statistics.