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

2008 ◽  
Vol 2 (1) ◽  
pp. 153-159 ◽  
Author(s):  
Lidiane Buligon ◽  
Gervásio A. Degrazia ◽  
Charles R.P. Szinvelski ◽  
Antonio G. Goulart
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Planetary Boundary Layer ◽  
Convective Boundary Layer ◽  
Gaussian Model ◽  
Alternative Formulation ◽  
Dispersion Parameters ◽  
Concentration Data ◽  
Convective Boundary ◽  
Algebraic Formulation

An alternative formulation for the dispersion parameters in a convective boundary layer is presented. The development 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 observational 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 dispersion 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 dispersion parameters, are shown to agree with the measurements of Copenhagen.

scholarly journals Vertical velocity and turbulence aspects during Mistral events as observed by UHF wind profilers

2004 ◽  
Vol 22 (11) ◽  
pp. 3927-3936 ◽  
Author(s):  
J.-L. Caccia ◽  
V. Guénard ◽  
B. Benech ◽  
B. Campistron ◽  
P. Drobinski
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Vertical Velocity ◽  
Convective Boundary Layer ◽  
Dissipation Rate ◽  
Convective Boundary ◽  
Turbulent Dissipation ◽  
The Alps ◽  
Rhone Valley ◽  
Wind Profilers

Abstract. The general purpose of this paper is to experimentally study mesoscale dynamical aspects of the Mistral in the coastal area located at the exit of the Rhône-valley. The Mistral is a northerly low-level flow blowing in southern France along the Rhône-valley axis, located between the French Alps and the Massif Central, towards the Mediterranean Sea. The experimental data are obtained by UHF wind profilers deployed during two major field campaigns, MAP (Mesoscale Alpine Program) in autumn 1999, and ESCOMPTE (Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transports d'Emission) in summer 2001. Thanks to the use of the time evolution of the vertical profile of the horizontal wind vector, recent works have shown that the dynamics of the Mistral is highly dependent on the season because of the occurrence of specific synoptic patterns. In addition, during summer, thermal forcing leads to a combination of sea breeze with Mistral and weaker Mistral due to the enhanced friction while, during autumn, absence of convective turbulence leads to substantial acceleration as low-level jets are generated in the stably stratified planetary boundary layer. At the exit of the Rhône valley, the gap flow dynamics dominates, whereas at the lee of the Alps, the dynamics is driven by the relative contribution of "flow around" and "flow over" mechanisms, upstream of the Alps. This paper analyses vertical velocity and turbulence, i.e. turbulent dissipation rate, with data obtained by the same UHF wind profilers during the same Mistral events. In autumn, the motions are found to be globally and significantly subsident, which is coherent for a dry, cold and stable flow approaching the sea, and the turbulence is found to be of pure dynamical origin (wind shears and mountain/lee wave breaking), which is coherent with non-convective situations. In summer, due to the ground heating and to the interactions with thermal circulation, the vertical motions are less pronounced and no longer have systematic subsident charateristics. In addition, those vertical motions are found to be much less developed during the nighttimes because of the stabilization of the nocturnal planetary boundary layer due to a ground cooling. The enhanced turbulent dissipation-rate values found at lower levels during the afternoons of weak Mistral cases are consistent with the installation of the summer convective boundary layer and show that, as expected in weaker Mistral events, the convection is the preponderant factor for the turbulence generation. On the other hand, for stronger cases, such a convective boundary layer installation is perturbed by the Mistral.

scholarly journals Derivation of the Turbulent Time Scales and Velocity Variances from LES Spectral Data: Application in a Lagrangian Stochastic Dispersion Model

2014 ◽  
Vol 8 (1) ◽  
pp. 16-21 ◽  
Author(s):  
S. Maldaner ◽  
G. A. Degrazia ◽  
U. Rizza ◽  
S. B.A. Rolim ◽  
O. C. Acevedo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Spectral Data ◽  
Time Scales ◽  
Convective Boundary Layer ◽  
Dispersion Model ◽  
Concentration Data ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Turbulence Data ◽  
Velocity Variances

Turbulent time scales and velocity variances for a convective boundary layer are derived from large eddy simulation spectral data. Spectral peak frequencies obtained from LES data are used directly in expressions that allow establishing such times scales and velocity variances. These turbulent parameters were compared with those provided by experimental turbulence data. The comparison employing a stochastic dispersion model and observed concentration data shows that both parameterizations reproduce adequately the contaminant dispersion process in a convective boundary layer.

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