The Structure of the Two-Dimensional Internal Boundary Layer over a Sudden Change of Surface Roughness

Rao, K. Shankar; Wyngaard, J. C.; Coté, Owen R.

doi:10.1175/1520-0469(1974)031<0738:tsottd>2.0.co;2

Cited by 219 publications

(136 citation statements)

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“…The upper level of the transition layer constitutes the top of the internal boundary layer. Floors et al (2011) found, from an analysis of measurements at Høvsøre, that the height of the internal boundary layer for momentum and wind velocity are different, in agreement with results from classical model simulations of the internal boundary layer, such as those of Rao et al (1974) and Peterson (1969). It was found that the flow at Høvsøre was in full equilibrium with the land surface below 15 m; followed by a transition layer in which the wind velocity conforms to that over the sea; the top of this layer is at ≈80 m and above this the marine wind profile prevails although the momentum is still in a transition phase between sea and land conditions.…”

Section: Reversal-height Analysissupporting

confidence: 56%

Weibull Wind-Speed Distribution Parameters Derived from a Combination of Wind-Lidar and Tall-Mast Measurements Over Land, Coastal and Marine Sites

Gryning

Floors

Peña

et al. 2015

Boundary-Layer Meteorol

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Wind-speed observations from tall towers are used in combination with observations up to 600 m in altitude from a Doppler wind lidar to study the long-term conditions over suburban (Hamburg), rural coastal (Høvsøre) and marine (FINO3) sites. The variability in the wind field among the sites is expressed in terms of mean wind speed and Weibull distribution shape-parameter profiles. The consequences of the carrier-to-noise-ratio (CNR) threshold-value choice on the wind-lidar observations are revealed as follows. When the wind-lidar CNR is lower than a prescribed threshold value, the observations are often filtered out as the uncertainty in the wind-speed measurements increases. For a pulsed heterodyne Doppler lidar, use of the traditional -22 dB CNR threshold value at all measuring levels up to 600 m results in a ≈7 % overestimation in the long-term mean wind speed over land, and a ≈12 % overestimation in coastal and marine environments. In addition, the height of the profile maximum of the shape parameter of the Weibull distribution (so-called reversal height) is found to depend on the applied CNR threshold; it is found to be lower at small CNR threshold values. The reversal height is greater in the suburban (high roughness) than in the rural (low roughness) area. In coastal areas the reversal height is lower than that over land and relates to the internal boundary layer that develops downwind from the coastline. Over the sea the shape parameter increases towards the sea surface. A parametrization of the vertical profile of the shape parameter fits well with observations over land, coastal regions and over the sea. An applied model for the dependence of the reversal height on the surface roughness is in good agreement with the observations over land.

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Section: Reversal-height Analysissupporting

confidence: 56%

Weibull Wind-Speed Distribution Parameters Derived from a Combination of Wind-Lidar and Tall-Mast Measurements Over Land, Coastal and Marine Sites

Gryning

Floors

Peña

et al. 2015

Boundary-Layer Meteorol

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“…4b (squares) with those obtained from the log law (triangles). It can be seen that the friction velocity decreases with fetch until an equilibrium value is reached, as already observed by Rao et al (1974) for a boundary layer over a change of surface roughness. In the case of a newly developing boundary layer under a free-stream flow, a detailed discussion of the evolution of u * is given in Castro (2007).…”

Section: Mean Velocity Fieldsupporting

confidence: 80%

Experimental Investigation of Turbulent Momentum Transfer in a Neutral Boundary Layer over a Rough Surface

Tomas

Eiff

Masson

2010

Boundary-Layer Meteorol

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The turbulent characteristics of the neutral boundary layer developing over rough surfaces are not well predicted with operational weather-forecasting models. The problem is attributed to inadequate mixing-length models, to the anisotropy of the flow and to a lack of controlled experimental data against which to validate numerical studies. Therefore, in order to address directly the modelling difficulties for the development of a neutral boundary layer over rough surfaces, and to investigate the turbulent momentum transfer of such a layer, a set of hydraulic flume experiments were carried out. In the experiments, the mean and turbulent quantities were measured by a particle image velocimetry (PIV) technique. The measured velocity variances and fluxes (u i u j ) in longitudinal vertical planes allowed the vertical and longitudinal gradients (∂/∂z and ∂/∂ x) of the mean and turbulent quantities (fluxes, variances and third-order moments) to be evaluated and the terms of the evolution equations for ∂e/∂t, ∂u 2 /∂t, ∂w 2 /∂t and ∂u w /∂t to be quantified, where e is the turbulent kinetic energy. The results show that the pressure-correlation terms allow the turbulent energy to be transferred equitably from u 2 to w 2 . It appears that the repartition between the constitutive terms of the budget of e, u 2 , w 2 and u w is not significantly affected by the development of the rough neutral boundary layer. For the whole evolution, the transfers of energy are governed by the same terms that are also very similar to the smooth-wall case. The PIV measurements also allowed the spatial integral scales to be computed directly and to be compared with the dissipative and mixing length scales, which were also computed from the data.

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“…This is based on consideration of fetch criteria yielding 1-2 m as a critical level where the nearest local roughness changes may induce an internal boundary (Rao et al, 1974;Bradley, 1988). A corresponding sensitivity study proves that using data from the upper measurement level (4 m) does not critically change the flux calculations.…”

Section: The Modelmentioning

confidence: 99%

The mass and energy balance of ice within the Eisriesenwelt cave, Austria

Obleitner

Spötl

2011

The Cryosphere

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Abstract. Meteorological measurements were performed in a prominent ice cave (Eisriesenwelt, Austria) during a full annual cycle. The data show the basic features of a dynamically ventilated cave system with a well distinguished winter and summer regime.The calculated energy balance of the cave ice is largely determined by the input of long-wave radiation originating at the host rock surface. On average the turbulent fluxes withdraw energy from the surface. This is more pronounced during winter due to enhanced circulation and lower humidity. During summer the driving gradients reverse sign and the associated fluxes provide energy for melt.About 4 cm of ice were lost at the measurement site during a reference year. This was due to some sublimation during winter, while the major loss resulted from melt during summer. Small amounts of accumulation occurred during spring due to refreezing of seepage water.These results are largely based on employing a numerical mass and energy balance model. Sensitivity studies prove reliability of the calculated energy balance regarding diverse measurement uncertainties and show that the annual mass balance of the ice strongly depends on cave air temperature during summer and the availability of seepage water in spring.

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The Structure of the Two-Dimensional Internal Boundary Layer over a Sudden Change of Surface Roughness

Cited by 219 publications

References 0 publications

Weibull Wind-Speed Distribution Parameters Derived from a Combination of Wind-Lidar and Tall-Mast Measurements Over Land, Coastal and Marine Sites

Weibull Wind-Speed Distribution Parameters Derived from a Combination of Wind-Lidar and Tall-Mast Measurements Over Land, Coastal and Marine Sites

Experimental Investigation of Turbulent Momentum Transfer in a Neutral Boundary Layer over a Rough Surface

The mass and energy balance of ice within the Eisriesenwelt cave, Austria

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