Quasi-Experimental Determination of Turbulent Dispersion Parameters for Different Stability Conditions from a Tall Micrometeorological Tower

Abstract

Turbulent wind data measured by sonic anemometers installed at various heights on a 140-m-tall micrometeorological tower located at a coastal site are used to obtain vertical profiles of the velocity standard deviations σi, Lagrangian decorrelation local time scales TLi, and eddy diffusivities Kα for distinct stability conditions. The novelty of the study lies in the use of turbulent data directly measured over the extension of the atmospheric surface layer at a coastal site for that purpose. Furthermore, the approach employs the Hilbert–Huang transform to determine the wind energy spectral peak frequencies. These are applied to the asymptotic spectral equation from Taylor statistical diffusion theory to obtain the turbulent dispersion parameters, which are shown to generally agree well with those provided by a classical autocorrelation approach. For neutral and stable situations the vertical profiles of momentum eddy diffusivities agree well with those derived from the spectral and autocorrelation method. Additionally, the turbulent integral time scales and eddy diffusivities determined by the method at a coastal location are found to overestimate those predicted from analytical expressions based on continental field observations. The turbulence parameters found are suitable to be employed in air pollution dispersion models.

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

“…where u i is the wind speed turbulent fluctuation and τ is the temporal lag. Recently, Martins et al (2018) used Eqs. ( 10), ( 11) and ( 12) to derive experimental vertical profiles for K x , K y and K z .…”

“…Most of the eddy diffusivities employed in current operational dispersion models are based on PBL similarity theories (Leelőssy et al, 2014). However, a better description of the turbulent properties, associated with eddy diffusivities, is based on direct measurements of wind data with high vertical resolution (Martins et al, 2018).…”

“…The turbulent wind data were obtained from high-frequency measurements (10 Hz) accomplished by tridimensional sonic anemometers at heights of 1, 2, 5, 9, 20, 37, 56, 75, 94, 113 and 132 m (Martins et al, 2018). Therefore, the study of Martins et al (2018) employs these measurements, the turbulent energy spectra and a few mathematical relations to determine turbulent dispersion pa-rameters (Taylor statistical diffusion theory, Degrazia et al, 2000Degrazia et al, , 2001.…”

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

“…Recently, (Martins et al, 2018) used Eqs. 11, 12 and 13 to derive experimental vertical profiles for K x , K y and K z .…”

“…The K x,y,z turbulent parameters were calculated from these turbulent wind data utilizing the Taylor statistical diffusion theory (Degrazia et al, 2000(Degrazia et al, , 2001. From this analysis the vertical profiles of these quasi-empirical determined eddy diffusivities were obtained by Martins et al (2018). The aim of this study is to obtain algebraic formulations, from the fitting curves, that reproduce the observed vertical profile of these quasi-experimental eddy diffusivities.…”