Antonio Goulart

Atmospheric Turbulence Decay During the Solar Total Eclipse of 11 August 1999

The studies of turbulence decay were based in the past on measurements carried out in neutrally stratified wind tunnels and, more recently, on large-eddy simulation runs. Here the atmospheric turbulence decay process during the solar total eclipse of 11 August 1999 is examined. Thus a rapid transition from convective boundary-layer turbulence to that of a neutral or slightly stable one is considered. A u-v-w propeller anemometer and a fast response temperature sensor located in northern France on top of a 9-m mast recorded the turbulence observations. The measurements, in terms of turbulent kinetic energy decay with time, were found to be in good agreement with those prescribed by a theoretical model of turbulence decay recently proposed. In particular, it was found that the exponent of the power law describing the decay process has the value -2.

Algebraic Formulation for the Dispersion Parameters in an Unstable Planetary Boundary Layer: Application in the Air Pollution Gaussian Model

An alternative formulation for the dispersion parameters in a convective boundary layer is presented. The de- velopment consists of a simple algebraic relation for the dispersion parameters, originated from the fitting of experimental data, in which the turbulent velocity variances and the Lagrangian decorrelation time scales are derived from the turbulent kinetic energy convective spectra. Assuming homogeneous turbulence for elevated regions in an unstable planetary boundary layer (PBL), the present approach, which provides the dispersion parameters, has been compared to the observa- tional data as well as to results obtained by classical complex integral formulations. From this comparison yields that the vertical and lateral dispersion parameters obtained from the simple algebraic formulas reproduce, in an adequate manner, the spread of contaminants released by elevated continuous source in an unstable PBL. Therefore, the agreement with dis- persion parameters available by an integral formulation indicates that the hypothesis of using an algebraic formulation as a surrogate for dispersion parameters in the turbulent convective boundary layer is valid. In addition, the algebraic vertical and lateral dispersion parameters were introduced into an air pollution Gaussian diffusion model and validated with the concentration data of Copenhagen experiments. The results of such Gaussian model, incorporating the algebraic disper- sion parameters, are shown to agree with the measurements of Copenhagen.

An Eddy Diffusivity Derivation for the Non-Isotropic Convective Decaying Turbulence in the Residual Layer

Eddy diffusivities are properties of turbulent flow that describe the magnitude of the dispersion in a Planetary Boundary Layer (PBL). Recently, a great number of works have been carried out to derive eddy diffusivities in a Convective and Stable Boundary Layer (CBL and SBL). However, little attention has been paid to derive vertical eddy diffusivities in a situation of decaying turbulence in the Residual Layer.

A comparison of two turbulent dispersion parameterisations in the stable boundary layer using Lagrangian and Eulerian models

An Eulerian model and a Lagrangian particle model are used to study the dispersion of a contaminant released from a low height source in the Stable Boundary Layer (SBL). The Eulerian model is based on the solution of the advection-diffusion equation by the Laplace transform technique. The Lagrangian model is based on a generalized form of the Langevin equation. Turbulence inputs are parameterised according to two procedures capable of generating continuous values in all stability conditions and in all heights of Planetary Boundary Layer (PBL). Statistical indices were calculated to compare the predicted and observed values of ground-level concentration. According to the statistical analysis, predicted concentration values agree well with the observed ones.

A solution of nonlinear equation for the gravity wave spectra from Adomian decomposition method: a first approach

In this paper, the equation for the gravity wave spectra in mean atmosphere is analytically solved without linearization by the Adomian decomposition method. As a consequence, the nonlinear nature of problem is preserved and the errors found in the results are only due to the parameterization. The results, with the parameterization applied in the simulations, indicate that the linear solution of the equation is a good approximation only for heights shorter than ten kilometers, because the linearization the equation leads to a solution that does not correctly describe the kinetic energy spectra.

Simulation of the Dispersion of Pollutants Considering Nonlocal Effects in the Solution of the Advection-Diffusion Equation

A way to solve the problem of closing the advection-diffusion equation is based on the transport hypothesis by gradient that, in analogy with molecular diffusion, assumes that the turbulent flux of concentration is proportional to the magnitude of the gradient of medium concentration. This work differs from the traditional method; a generic equation is used for the turbulent diffusion being considered that the flux more yours derived is proportional to the medium gradient. This way, an equation is obtained that takes into account the asymmetry in the process of dispersion of atmospheric pollutants. Therefore, the proposal of this work is to obtain an analytic solution of this new equation using the Laplace Transform technique, considering the Convective Boundary Layer (CBL) as a multilayer system. To investigate the influence of the nonlocal effects in the turbulent dispersion process, the model is evaluated against atmospheric dispersion experiments that were carried out in Copenhagen under unstable conditions.

Poster 24 One-dimensional eddy diffusivities for growing turbulence in the convective boundary layer

Abstract In this work a general method to derive eddy diffusivities in a convective growing turbulence in the planetary boundary layer is proposed. The method is based in a model for the budget equation describing the 3-D energy density spectrum and the Taylor statistical diffusion theory.

SIMULAÇÕES LES DE UMA CAMADA LIMITE CONVECTIVA EMPREGANDO UM ESPAÇAMENTO DE GRADE VERTICAL VARIÁVEL

Simulacoes LES de uma camada limite convectivaempregando um espacamento de grade vertical variave

COMPARAÇÃO ENTRE OS PARÂMETROS DE DISPERSÃO ALGÉBRICO E CLÁSSICO VIA MODELO DE PLUMA GAUSSIANA

Comparacao entre os parâmetros de dispersao algebrico eclassico via Modelo de Pluma Gaussiana

Dispersion of pollutants from an elevated source in the Residual Layer: the influence of the convective decaying turbulence in the ground-level concentration

About half hour before sunset over land, the surface heat flux (positive during the day) begins to decrease and then, during night-time, becomes negative and, consequently, a stable boundary layer (SBL) develops near the ground. Above this SBL, the convective boundary layer (CBL) starts to decay. In this study, employing simulations with a Eulerian analytical diffusion model, the influence of this decaying convective turbulence in the dispersion of contaminants is investigated. The important case of pollutants released from a tall stack during the characteristic sunset transition time (about one hour) is considered.