A Lagrangian Decorrelation Time Scale in the Convective Boundary Layer

A new method for deriving the Lagrangian decorrelation time scales for inhomogeneous turbulence is described. The expression for the time scales here derived for the convective boundary layer is compared to those estimated by Hanna during the Phoenix experiment. Then the values of C₀, the Lagrangian velocity structure function constant, and of B_i, the Lagrangian velocity spectrum constant, were evaluated from the Eulerian velocity spectra and from the Lagrangian time scales derived, under unstable conditions, from Taylor's statistical diffusion theory. The numerical coefficient of the lateral and vertical Lagrangian spectra in the inertial subrange was found equal to 0.21, in good agreement with previous experimental estimates.     

Vertical Profiles of Turbulence Parameters in the Thermal Internal Boundary Layer

Boundary-Layer Meteorology - The correct simulation of pollutant dispersion in coastal regions demands understanding the turbulence structure of the thermal internal boundary layer (TIBL), which...     

Turbulence Intensity Parameters over a Very Complex Terrain

Detailed knowledge of turbulence structure is important for the understanding of atmospheric phenomena in the boundary layer, especially over complex terrain. In the present study, turbulence intensity parameters are analyzed for different conditions regarding stability, wind speed and wind direction over a mountainous region. The purpose of the analysis is to verify whether the observed parameters follow Monin–Obukhov similarity theory (MOST), despite the terrain heterogeneity. The dataset was collected during an experimental campaign at the Nova Roma do Sul site, in southern Brazil, with a micrometeorological tower located near a sharp slope, approximately 400 m high. The results show that the normalized standard deviations of the vertical velocity component as well as the normalized standard deviation of temperature follow Monin–Obukhov similarity for all stability regimes, regardless of the wind direction. However the normalized standard deviation of the horizontal components of the turbulent velocity obeys the similarity relationship only for a limited range of the stability parameters.     

Theoretical considerations of meandering winds in simplified conditions

The influence of turbulence on the meandering phenomenon is investigated. The study, based on the three-dimensional Navier–Stokes equations, shows that when the turbulent fluxes can be neglected an asymptotic solution results. This solution reproduces a horizontal wind oscillation with an infinite relaxation time. When there is turbulent forcing, on the other hand, a transition occurs to a new order, characterized by a spatial reorganization, leading to a wind field with a well-defined direction.     

A Theoretical Model for the Study of Convective Turbulence Decay and Comparison with Large-Eddy Simulation Data

The development of a theoretical model fora decaying convective boundary layeris considered. The model relies on thedynamical energy spectrumequation in which the buoyancy andinertial transfer terms are retained,and a closure assumptionmade for both. The parameterization for thebuoyancy term is given providing a factorizationbetween the energy source termand its temporal decay. Regarding the inertialtransfer term a hypothesis ofsuperposition is used to describe theconvective energy source and time variationof velocity correlation separately.The solution of the budget equation for theturbulent kinetic energy spectrum is possible,given the three-dimensional initial energyspectrum. This is doneutilizing a version of the Kristensen et al.(see Boundary-Layer Meteorol. 47, 149–193)model valid for non-isotropic turbulence. During thedecay the locus of the spectralpeak remains at about the sameposition as the heat flux decreases.Comparison of the theoretical modelis performed against large-eddy simulationdata for a decaying convectiveboundary layer.