Numerical simulation of internal boundary-layer development and comparison with atmospheric data     

János Józsa  Barbara Milici  Enrico Napoli 《Boundary-Layer Meteorology》2007,123(1):159-175

A finite-volume numerical model is employed to investigate the adaptation of the atmospheric boundary layer to a change in the underlying surface roughness, such as that existing in the transition from land to the free surface of a water body. Numerical results are validated by comparison with neutral stratification atmospheric data and compared with the internal boundary-layer (IBL) heights computed using a number of existing empirical formulae. The numerical analysis allows an extension of the fetch range in which the existing formulae, calibrated only by comparison with short fetch data, may be applied. An argument is offered that the spatial variability of the water surface roughness should be also taken into account for the IBL development over the surface of a water body.  相似文献   

Simulation Of Urban-Scale Dispersion Using A Lagrangian Stochastic Dispersion Model   总被引：4，自引：1，他引：3  

Mathias W. Rotach 《Boundary-Layer Meteorology》2001,99(3):379-410

  相似文献   

An Approximate Analytical Solution Of Flux-Profile Relationships For The Atmospheric Surface Layer With Different Momentum And Heat Roughness Lengths   总被引：3，自引：1，他引：2  

K. Blümel 《Boundary-Layer Meteorology》2000,97(2):251-271

An approximate method for calculating the relationship between z/L(z = reference height, L = Obukhov length) and the bulk Richardsonnumber is presented. If this relationship is known, the momentum andheat fluxes can be computed easily without any iteration. The avoidance of iteration can speed up computationsin large-scale models considerably (up to 10 times) and cases which do not converge or converge very slowly cannot occur. The proposed formulae take into account the difference between momentum (z_0M) and heat roughnesslengths (z_0H). Because the roughness lengths are not neglected at any step of the derivation, the resulting analytical formulae can be used not only between the surface and the reference height but also between two finite levels z₁ andz₂ (by replacing z_0M and z_0H by z₁ and z by z₂). Theequations remain correct even in the limit z₁ z₂.The formulae are based upon the (partially modified) Businger–Dyer flux–profile relationships and,consequently, they are restricted to predominantly homogeneous terrain.These new approximations are an improvement over the existing solutions because they are simpler than most of the formulae in the literature and are able to match the numerical exact solution for different parameter sets (Businger, Dyer, Högström) with an maximum error of about 2% for a wide range of z/L, z/z_0M and z_0M/z_0H.Furthermore, in stable conditions, schemes with and without a finitecritical bulk Richardson number can be approximated. The possibleambiguity of the exact solution =f(RI_B) in (moderately) stable conditions is discussed briefly. The performance of the new formulae is compared to the exact numerical solution and to different formulae proposed in the literature.  相似文献   

Investigation of natural rock joint roughness     

《Computers and Geotechnics》2014

The paper provides a comprehensive review on rock joint roughness measurement and quantification procedures. Superiority of fractal based methods over JRC, statistical parameters and statistical functions in quantifying roughness is discussed in the paper. Two of the best fractal based methodologies available in the literature, the modified 2-D divider and variogram methods, are used to quantify natural rock joint roughness in 3-D and 2-D, respectively. The capability of these two methods in accurate quantification of natural rock joint roughness is shown in the paper by applying the procedures to four natural rock joints. A good comparison has been obtained from the values obtained through the two methods. Both these methodologies have two parameters to capture the stationary roughness. The fractal dimension captures the spatial auto correlation of roughness; the other parameter captures the amplitude of roughness. Anisotropic roughness has been studied by applying two other methodologies: (a) a triangular plate methodology and (b) a light source methodology to the same four natural rock joints. A reasonably good comparison has been obtained through the results of these two methodologies. All four roughness quantification methodologies can be applied to any size of sample covering from laboratory to field scales. The results of the triangular plate and light source methodologies provided possible sliding direction values (under the gravitational loading) close to that reported in the literature for the rough discontinuity planes used in the study.  相似文献   

Methodological Considerations Regarding the Measurement of Turbulent Fluxes in the Urban Roughness Sublayer: The Role of Scintillometery     

Matthias Roth  Jennifer A. Salmond  A. N. V. Satyanarayana 《Boundary-Layer Meteorology》2006,121(2):351-375

We address some of the methodological challenges associated with the measurement of turbulence and use of scintillometers in the urban roughness sublayer (RSL). Two small-aperture scintillometers were located near the roof interface in a densely urbanized part of Basel, Switzerland, as part of the Basel Urban Boundary-Layer Experiment (BUBBLE) in the summer of 2002. Eddy correlation instruments were co-located near the mid-point of each scintillometer path for data verification purposes. The study presents the first values of the inner length scale of turbulence (l ₀) and the refractive index structure parameter of air for a city and demonstrates the influence of mechanical driven turbulence on dissipation. Comparison of dissipation values determined from the two approaches show large scatter that is possibly due to the spatial inhomogeneity of the turbulence statistics within the RSL. Velocity and temperature spectra display a −2/3 slope in the inertial subrange, although the spectral ratio is less than the theoretical prediction of 4/3 expected for isotropy. Conventional Monin–Obukhov equations used to calculate fluxes from the scintillometer were replaced with urban forms of the equations. The results suggest that the scintillometer may be an appropriate tool for the measurement of sensible heat flux (Q _H ) above the rooftops given a suitable determination of the effective measurement height.  相似文献   

Influence of Obstacles on the Aerodynamic Roughness of the Netherlands     

Joost J. M. De Jong  Arjen C. De Vries  Wim Klaasen 《Boundary-Layer Meteorology》1999,91(1):51-64

The aim of this study was to analyse the influence of large- and small-scale obstacles (orography, tree lines, and dikes) on the effective aerodynamic roughness of the Netherlands, a relatively flat, small-scale landscape. The roughness averaging approach was based on drag coefficients. The effective roughness was locally dominated by small-scale obstacles such as tree lines and dikes. Even at a regional scale (40,000 km2), the small-scale obstacle drag was of the same order of magnitude as the shear stress due to landuse. The neglect of those obstacles on a regional scale would result in approximately 10% overestimated averaged windspeed at 10~m above the surface. It was concluded that small-scale obstacles need to be taken into account to calculate the aerodynamic roughness of flat landscapes. Orography was of minor importance in this lowland country.  相似文献   

Aerodynamic Variables in the Bulk Formulation of Turbulent Fluxes   总被引：1，自引：1，他引：0  

Jielun Sun  William Massman  David A Grantz 《Boundary-Layer Meteorology》1999,91(1):109-125

Aerodynamic variables are required to apply Monin–Obukhov similarity theory in the bulk formulation of surface fluxes. In the literature, these aerodynamic variables are commonly misinterpreted. In this paper, we review the concept of the aerodynamic variable, its connection to surface-layer similarity theory and how and why the aerodynamic variable is replaced with other variables.Observed mean variables below the surface layer, such as the surface radiation temperature, or the air temperature at canopy height, are often used in place of the extrapolated aerodynamic variables in the bulk formula, requiring empirical relationships between aerodynamic and observed variables, or requiring empirical adjustments of bulk resistances. The present study examines the validity of these relationshi Experiment (CODE). The results indicate that using a measured substitute for an aerodynamic variable can lead to significant errors in estimates of turbulent surface fluxes.  相似文献   

Landscape Roughness Parameters for Sherwood Forest – Validation of Aggregation Models     

M. Bottema 《Boundary-Layer Meteorology》1998,89(2):317-347

Various models for calculating the effective or area-averaged roughness length zoe have been tested for a partly forested area. Three types of model are considered: the tile approach for very large scales of inhomogeneity (> 20 km), drag models for very small scales (up to 1 km), and surface-layer methods such as the blending-height method for intermediate scales. Over partly forested areas, where both pressure effects and roughness sub-layer effects may become significant, small-scale models are expected be the most suitable type of model. The various model types were tested against new experimental data that were obtained over the partly forested Sherwood Forest area (UK). The best fit with the data was obtained with the blending-height method, rather than with the different small-scale models. This is remarkable as the surface-layer assumptions of the blending-height method were clearly violated: the calculated blending height was 7 m, as compared to the mean tree height of 20 m. Of the small-scale models, a sparse-canopy approach compared poorly with the experimental data. The drag models overestimated the area-averaged roughness to a lesser degree, but a major point of concern remains the choice of the model parameters. Therefore, suggestions are made for an improved choice of these parameters.  相似文献   

表面粗糙度对海浪成长率的影响     

董力耘  袁业立 《海洋科学进展》1997,(1)

本文在Miles准层流风生波模型基础上，引入表面粗糙度滑波面不均匀分布的线性模型，通过不稳定性分析，导出了平均压力随表面粗糙度变化和海浪成长率之间的关系，表明表面粗糙度的不均匀分布是影响海浪成长率的一个重要因素。  相似文献   

SURFACE-LAYER SCALING FOR THE CONVECTION-INDUCED STRESS REGIME     

A. A. GRACHEV  C. W. FAIRALL  S. S. ZILITINKEVICH 《Boundary-Layer Meteorology》1997,83(3):423-439

The Prandtl, Obukhov, and Monin andObukhov similarity theories are widely used todescribe the structure of turbulence in theatmospheric surface layer. Currently it isunderstood that in strong convection with no or veryweak mean wind the traditional theory breaks down.In particular, the traditional theory implies asingle-valued correspondence between localturbulence statistics and local properties ofthe flow. In very strong convection, this is nottrue because of large-scale ( 10 3 m) coherentstructures, embracing the entire convective boundarylayer (CBL). These structures produce random guststhat crucially affect surface-layer turbulence andmake it dependent on global properties of theflow, such as the CBL depth. In the present paperthe limits of validity of the traditional surface-layer similarity theory are determined and a revisedtheory of fair weather convection in the surface layeris developed by considering the effect of gustiness. It is shownthat the theoretical predictions are consistent withfield data from the TOGA COARE and SCOPEexperiments.  相似文献