Critical Test of the Validity of Monin–Obukhov Similarity during Convective Conditions

Abstract

A recent study of convective boundary layer characteristics performed with large eddy simulation technique (LES) has demonstrated unexpected influence of the depth of the boundary layer on surface layer characteristics. The present study tests some of the predictions from these simulations with field measurements from a summertime experiment in Sweden, which includes in addition to regular surface layer data also airborne measurements and numerous radio soundings, which enable accurate determination of boundary layer depth. It is found that the measurements strongly support most of the conclusions draws from the LES study and give additional information over a wider stability range. Thus, the normalized wind gradient m is found to depend on both z/L, where z is height above the ground and L is the Monin-Obukhov length, and z i /L, where z i is the height of the convective boundary layer. This additional dependence on z i /L explains much of the scatter between experiments encountered for this parameter. In the case of the normalized temperature gradient h , the experimental data follow the generally accepted functional relation with z/L, but with an additional, slight ordering according to z i /L. Analyses of nondimensional variances show (i) the horizontal velocity variance scales on mixed layer variables and is a function only of z i /L, in agreement with the LES results and with previous measurements; (ii) the normalized vertical velocity variance depends on the large-scale pressure gradient length scale for slight instability and is primarily a function of z /L for moderate and strong instability; (iii) the normalized temperature variance is a function of z/L, with a possible slight dependence on z i /L; and (iv) whereas mean temperature gradient is characterized by local shear scales, temperature variances are normalized by local buoyancy-driven scales.

Analysis of second‐order moments in surface layer turbulence in an Alpine valley

“…The measurement height scaled with L, turned out to be the only relevant lengthscale, neglecting any possible dependence on the mixing height h, which was suggested as a proper scaling parameter under unstable conditions (Högström, 1996;Khanna and Brasseur, 1997;Johansson et al, 2001). On the other hand, one may hypothesise that other geometrical scales (such as valley width, sidewall slopes, etc.)…”

Monin–Obukhov Similarity Functions of the Structure Parameter of Temperature and Turbulent Kinetic Energy Dissipation Rate in the Stable Boundary Layer

“…Andreas and Hicks (2002) show how errors in u à affect the scatter in / m and / h against f plots. Johansson et al (2002) replied to this by stating that also the effect of errors in h * should be included. We performed such an analysis for f e -f and f T -f plots, which shows that errors in u à lead to a displaced f e -f pair that moves along the fitting curve, while a f T -f pair moves normal to it.…”

Dispersion modeling of air pollutants in the atmosphere: a review

“…(6) are parameterized based on the vertical profiles obtained from the Monin-Obukhov-theory ( Figure 1) [3]. The Monin-Obukhov theory was validated against numerous measurement and advanced computational fluid dynamics datasets, and although some weaknesses were shown, it still provides the most reliable basis for all fields of atmospheric modeling [3,9,10,[12][13][14]. Typical values of the Monin-Obukhov-length are given in Table 2.…”

“…A reaction mechanism consists of elementary reactions by which overall chemical change occurs. Chemical reactions can be described and calculated by a set of ordinary differential equations (ODEs) = α (13) where is the chemical rate coefficient for the reaction and α is the order of reaction with respect to chemical species . Radioactive decay differs from chemical reactions due to its nature, because during the radioactive decay the atomic properties are changed.…”

“…A state-of-the-art solution for turbulence modeling is Large Eddy Simulation (LES), which filters the large scale (anisotropic) and small scale (isotropic) eddies, and performs direct simulation on the former [134]. Despite its huge computational cost, LES has become a popular tool for planetary boundary layer case studies, and its results are often used as a verification dataset for other models [13,135]. CFD-based street canyon models are widely used to predict air quality in urban and industrial areas [59,[134][135][136][137][138][139].…”