scholarly journals TURBULENT EDDY DIFFUSIVITIES FOR A PLANETARY BOUNDARY LAYER GENERATED BY THERMAL AND MECHANICAL EFFECTS

2013 ◽  
Vol 31 (4) ◽  
pp. 609 ◽  
Author(s):  
André Becker Nunes ◽  
Gervásio Annes Degrazia ◽  
Cláudia Rejane Jacondino De Campos ◽  
Davidson Martins Moreira
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Mean Squared Error ◽  
Dispersion Model ◽  
Eddy Diffusivity ◽  
Advection Equation ◽  
Turbulent Eddy ◽  
Mechanical Effects ◽  
Boundary Layer Turbulence ◽  
Eddy Diffusivities

ABSTRACT. To estimate the superficial concentration of contaminants an eulerian model of dispersion was used, where the main scheme is the diffusion-advection equation that employs turbulent eddy diffusivity. The aim of this work is a comparison between different eddy diffusivity derivations for a planetary boundary layer turbulence generated by thermal and mechanical effects. The accuracy of eddy diffusivity derivations was evaluated by comparing the data simulated in the eulerian dispersion model and the observed concentrations of the Copenhagen and Praire Grass experiments. Three convective eddy diffusivity derivations were compared among themselves: 1) proposed by Degrazia et al., 2) proposed Hostlag & Moeng and 3) the derivation gotten by the parameters of Hanna. Two neutral eddy diffusivity derivations were also compared: 1) proposed by Degrazia et al. and 2) gotten by the parameters of Hanna. In order to improve the comparisons some adjustments and increments were made in Hostlag & Moeng derivation and in that gotten by the parameters of Hanna. We can observe that despite the eddy diffusivities having been formulated by different ways, the results were similar and sufficiently satisfactory. In the convective case, the best simulations of each derivation showed a Normalized Mean Squared Error between 0.04 and 0.05 when compared with Copenhagen dataset.Keywords: dispersion model, Taylor theory, lagrangean timescale. RESUMO. Na estimativa da concentração superficial de contaminantes foi usado um modelo de dispersão euleriano, tendo como esquema principal a equação de difusão-advecção que emprega coeficiente de difusão turbulento. O objetivo deste trabalho é a comparação entre diferentes derivações de coeficientes de difusão para uma camada limite planetária cuja turbulência é gerada por fatores térmicos e mecânicos. A precisão das derivações foi calculada por meio da comparação entre os dados simulados pelo modelo euleriano de dispersão e os dados de concentração observados nos experimentos de Copenhagen e Praire Grass. Três derivações de coeficientes de difusão convectivos foram comparadas: 1) a proposta por Degrazia et al., 2) a proposta por Hostlag & Moeng, e 3) a derivação obtida através dos parâmetros de Hanna. Também foram comparadas duas derivações de coeficientes de difusão neutros: 1) uma proposta por Degrazia et al. e 2) a obtida por meio dos parâmetros de Hanna. Para uma melhor comparação, foram feitos alguns ajustes nas derivações de Hostlag e Moeng e na obtida através dos parâmetros de Hanna. Pode-se observar que apesar das derivações serem obtidas por diferentes metodologias, os resultados foram similares e suficientemente satisfatórios. Para o caso convectivo, as melhores simulações de cada derivação apresentaram Erro Quadrático Médio Normalizado entre 0,04 e 0,05 quando comparados com os dados do experimento de Copenhagen.Palavras-chave: modelo de dispersão, teoria de Taylor, escala de tempo lagrangeana.

scholarly journals A quasi-experimental coastal region eddy diffusivity applied in the APUGRID model

2020 ◽  
Vol 38 (3) ◽  
pp. 603-610
Author(s):  
Silvana Maldaner ◽  
Michel Stefanello ◽  
Luis Gustavo N. Martins ◽  
Gervásio Annes Degrazia ◽  
Umberto Rizza ◽  
...  
Keyword(s):  
Dispersion Model ◽  
Sonic Anemometer ◽  
Coastal Region ◽  
Eddy Diffusivity ◽  
Turbulent Dispersion ◽  
Southeastern Brazil ◽  
Advection Equation ◽  
Concentration Data ◽  
Eddy Diffusivities ◽  
Quasi Experimental

Abstract. In this study, Taylor statistical diffusion theory and sonic anemometer measurements collected at 11 levels on a 140 m high tower located in a coastal region in southeastern Brazil have been employed to obtain quasi-empirical convective eddy diffusivity parameterizations in a planetary boundary layer (PBL). The derived algebraic formulations expressing the eddy diffusivities were introduced into an Eulerian dispersion model and validated with Copenhagen tracer experiments. The employed Eulerian model is based on the numerical solution of the diffusion–advection equation by the fractional step/locally one-dimensional (LOD) methods. Moreover, the semi-Lagrangian cubic-spline technique and Crank–Nicolson implicit scheme are considered to solve the advection and diffusive terms. The numerical simulation results indicate that the new approach, based on these quasi-experimental eddy diffusivities, is able to reproduce the Copenhagen concentration data. Therefore, the new turbulent dispersion parameterization can be applied in air pollution models.

scholarly journals A quasi-experimental coastal region eddy diffusivity applied in the APUGRID model

2019 ◽  
Author(s):  
Silvana Maldaner ◽  
Michel Stefanello ◽  
Luis Gustavo N. Martins ◽  
Gervásio Annes Degrazia ◽  
Umberto Rizza ◽  
...  
Keyword(s):  
Dispersion Model ◽  
Sonic Anemometer ◽  
Coastal Region ◽  
Eddy Diffusivity ◽  
Turbulent Dispersion ◽  
Southeastern Brazil ◽  
Advection Equation ◽  
Concentration Data ◽  
Eddy Diffusivities ◽  
Quasi Experimental

Abstract. In this study, Taylor statistical diffusion theory and sonic anemometer measurements collected at 11 levels on a 140-m high tower located at a coastal region in southeastern Brazil have been employed to obtain quasi-empirical convective eddy diffusivity parameterizations in a planetary boundary layer (PBL). The derived algebraic formulations expressing the eddy diffusivities were introduced into an Eulerian dispersion model and validated with Copenhagen tracer experiments. The employed Eulerian model is based on the numerical solution of the diffusion-advection equation by the Fractional Step/Locally One-Dimensional (LOD) methods. Moreover, the semi-Lagrangian cubic-spline technique and Crank-Nicholson implicit scheme are considered to solve the advection and diffusive terms. The numerical simulation results indicate that the new approach, based on these quasi-experimental eddy diffusivities, is able to reproduce the Copenhagen concentration data. Therefore, the new turbulent dispersion parameterization can be applied in air pollution models.

scholarly journals Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations

2015 ◽  
Vol 8 (10) ◽  
pp. 3393-3419 ◽  
Author(s):  
S. Nishizawa ◽  
H. Yashiro ◽  
Y. Sato ◽  
Y. Miyamoto ◽  
H. Tomita
Keyword(s):  
Boundary Layer ◽  
Energy Spectrum ◽  
Aspect Ratio ◽  
Planetary Boundary Layer ◽  
Temporal Integration ◽  
Mixing Length ◽  
Boundary Layer Turbulence ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy

Abstract. We examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (PBL) in a large-eddy simulation (LES). In order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological LES model with a fully explicit scheme of temporal integration. The influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. We confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical −5/3 slope of the energy spectrum. If we define the filter length in LES modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. We also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the PBL, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained.

scholarly journals Employing Spectral Analysis to Obtain Dispersion Parameters in an Atmospheric Environment Driven by a Mesoscale Downslope Windstorm

2021 ◽  
Vol 18 (24) ◽  
pp. 13027
Author(s):  
Cinara Ewerling da Rosa ◽  
Michel Stefanello ◽  
Silvana Maldaner ◽  
Douglas Stefanello Facco ◽  
Débora Regina Roberti ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Diffusion Theory ◽  
Dispersion Model ◽  
Atmospheric Dispersion ◽  
Particle Dispersion ◽  
Atmospheric Environment ◽  
Dispersion Parameters ◽  
Simulated Concentration ◽  
Four Levels

Considering the influence of the downslope windstorm called “Vento Norte” (VNOR; Portuguese for “North Wind”) in planetary boundary layer turbulent features, a new set of turbulent parameterizations, which are to be used in atmospheric dispersion models, has been derived. Taylor’s statistical diffusion theory, velocity spectra obtained at four levels (3, 6, 14, and 30 m) in a micrometeorological tower, and the energy-containing eddy scales are used to calculate neutral planetary boundary layer turbulent parameters. Vertical profile formulations of the wind velocity variances and Lagrangian decorrelation time scales are proposed, and to validate this new parameterization, it is applied in a Lagrangian Stochastic Particle Dispersion Model to simulate the Prairie Grass concentration experiments. The simulated concentration results were shown to agree with those observed.

scholarly journals Influence on the Temperature Estimation by the Planetary Boundary Layer Scheme with Different Minimum Eddy Diffusivity in WRF v3.9.1.1

2021 ◽  
Author(s):  
Hongyi Ding ◽  
Le Cao ◽  
Haimei Jiang ◽  
Wenxing Jia ◽  
Yong Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Urban Areas ◽  
Eddy Diffusivity ◽  
Mountain Areas ◽  
Temperature Estimation ◽  
Temperature Deviation ◽  
Stable Conditions ◽  
Pbl Scheme ◽  
Boundary Layer Scheme

Abstract. The minimum eddy diffusivity (Kzmin) in the planetary boundary layer (PBL) scheme is able to influence the performance of the model in simulating meteorological parameters such as the temperature. However, detailed studies on the sensitivities of the simulated temperature to the settings of Kzmin are still lacking. Thus, in this study, we evaluated the performance of the ACM2 (Asymmetrical Convective Model, version 2) scheme in the WRF (Weather Research and Forecasting) model with different settings of Kzmin, in simulating the spatiotemporal distribution of the temperature in the region of Beijing, China. Five constant values as well as a function were implemented in the model to calculate Kzmin, and the simulation results with different settings of Kzmin were compared and analyzed. The results show that the increase of Kzmin leads to an elevation of the 2-m temperature, especially in the nighttime. We figured out that the deviation of the 2-m temperature at night is mainly caused by the different estimation of the turbulent mixing under stable conditions in simulation scenarios with different Kzmin settings. Moreover, the spatial distribution of the temperature deviation indicates that under various underlying surface categories, the change of Kzmin exerts a different influence on the prediction of the 2-m temperature, and the influence was found stronger during the nighttime than during the daytime, in plain areas than in mountain areas, in urban areas than in non-urban areas. In the nighttime of the urban areas, the influence on the simulated 2-m temperature brought about by the change of Kzmin was found the strongest. In addition, we found that the implementation of a functional type Kzmin in the ACM2 scheme helps to improve the performance of the model in capturing the diurnal change and the vertical distribution of the temperature in this region, compared with that using a constant Kzmin.

Sign in / Sign up

Export Citation Format

Share Document