%0 Journal Article
%T Connecting Turbulence and Meandering Parameterization to Describe Passive Scalars Dispersion in Low Wind Speed Conditions
%A V. S. Moreira
%A G. Degrazia
%A A. U. Timm
%A D. R. Roberti
%A S. Maldaner
%J ISRN Atmospheric Sciences
%D 2013
%R 10.1155/2013/738024
%X The following study deals with meandering of the horizontal mean wind. The main motivation for such investigation came from the difficulty in describing contaminant dispersion in meandering conditions. Observational field measurements point out that the autocorrelation function of the horizontal wind components, obtained for the meandering cases, displays an oscillating behavior with the presence of large negative lobes. Such negative lobes are described by an equation containing functions that represent patterns of movement associated to meandering and turbulence. As a consequence, this mathematical formulation connects the turbulence and meandering phenomenon establishing the employment of hybrid parameters in models that describe the meandering dispersion. Therefore, considering this dualistic aspect between meandering and turbulence manifestations, a new set of relations for the turbulence parameterization joined with the meandering of the wind have been developed and are available. This new turbulence parameterization for a stable shear forcing planetary boundary layer, united with a meandering mean time scale is able to describe contaminant meandering enhanced spread in a low wind speed stable planetary boundary layer. 1. Introduction Low-frequency meandering of the horizontal mean wind vector occurring in low wind speed conditions is a complex physical phenomenon associated with turbulence in the stable planetary boundary layer (PBL) [1]. Using a number of simplifying assumptions in the three-dimensional Navier-Stokes equations [2], the influence of the Reynolds-stress terms on the meandering phenomenon has been analyzed. The study shows that when the turbulent forcing can be neglected, the Navier-Stokes equations provide an asymptotic meandering solution that describes a nondecaying horizontal wind oscillation. Differently, for increasing values of the turbulent forcing, the presence of the horizontal Reynolds-stress terms demonstrates that the action of turbulence changes the geometry of the flow field. In this aspect, the turbulent forcing imposes a finite relaxation time and transforms a two-dimensional flow to one-dimensional. Therefore, this new order of the flow, generated by the turbulence leads to a different spatial symmetry, establishing a precise mean wind direction and ceasing the meandering behavior to exist. Because PBL similarity theory fails to represent transport processes when winds are calm, it remains a difficult physical task to derive air pollution dispersion models that simulate meandering enhanced diffusion of passive
%U http://www.hindawi.com/journals/isrn.atmospheric.sciences/2013/738024/