Note on Aerodynamic Roughness-Parameter Estimation on the Basis of Roughness-Element Description

Lettau, H.

doi:10.1175/1520-0450(1969)008<0828:noarpe>2.0.co;2

Cited by 613 publications

(386 citation statements)

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“…sizes and spacing on the order of the size of the vortex core). Roughness is determined by the size and spacing of the nonerodible roughness elements and can be characterized by the roughness density, λ, also known as frontal-area index, defined by Lettau (1969) as…”

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confidence: 99%

Dust Devil Sediment Transport: From Lab to Field to Global Impact

et al. 2016

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The impact of dust aerosols on the climate and environment of Earth and Mars is complex and forms a major area of research. A difficulty arises in estimating the contribution of small-scale dust devils to the total dust aerosol. This difficulty is due to uncertainties in the amount of dust lifted by individual dust devils, the frequency of dust devil occurrence, and the lack of statistical generality of individual experiments and observations. In this paper, we review results of observational, laboratory, and modeling studies and provide an overview of dust devil dust transport on various spatio-temporal scales as obtained with the different research approaches. Methods used for the investigation of dust devils on Earth and Mars vary. For example, while the use of imagery for the investigation of dust devil occurrence frequency is common practice for Mars, this is less so the case for Earth. Modeling approaches for Earth and Mars are similar in that they are based on the same underlying

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confidence: 99%

Dust Devil Sediment Transport: From Lab to Field to Global Impact

et al. 2016

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“…The estimations of z d , proposed by Bottema (1995Bottema ( , 1997 and Macdonald et al (1998), where an empirical drag coefficient is also taken into account, are similar. The purely geometrical methods, developed by Kondo and Yamazawa (1986) and Lettau (1969) seem to overestimate the modelling of z 0 in comparison with the methods of Bottema (1995Bottema ( , 1997 and Macdonald et al (1998). The latter values of z 0 are close to the desired value of z 0 /δ for a medium roughness surface.…”

Section: Roughness Elementsmentioning

confidence: 70%

“…For later comparison with the measurements and for the initial design of the surface layout, several models to estimate the roughness length z 0 , as well as the displacement length z d , based on the above mentioned geometrical densities, were evaluated. The results, based on the models of Kondo and Yamazawa (1986), Bottema (1995Bottema ( , 1997, Lettau (1969) and Macdonald et al (1998), are given in Table 2. The estimations of z d , proposed by Bottema (1995Bottema ( , 1997 and Macdonald et al (1998), where an empirical drag coefficient is also taken into account, are similar.…”

Section: Roughness Elementsmentioning

confidence: 99%

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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“…The rotational frequency of the· earth is 0 = ~ hour-I. Outcalt (1972aOutcalt ( ,1972b) developed a one-dimensional surface-layer model (SLM), expanding primarily on the work of Myrup (1969) and Lettau (1969 Carlson and Borland (1978) produced a one-dimensional BLM. This model is used primarily to simulate surface fluxes and surface temperature, but it also uses Monin-Obukhov similarity theory to estimate wind velocity, air temperature, and specific humidity at various heights.…”

Section: Surface-layer Modelsmentioning

confidence: 99%

Role of surface characteristics in urban meteorology and air quality

Sailor

1993

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Note on Aerodynamic Roughness-Parameter Estimation on the Basis of Roughness-Element Description

Cited by 613 publications

References 1 publication

Dust Devil Sediment Transport: From Lab to Field to Global Impact

Dust Devil Sediment Transport: From Lab to Field to Global Impact

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

Role of surface characteristics in urban meteorology and air quality

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