Relationships Between Second and Third Moments in the Surface Layer Under Different Stratification over Grassland and Urban Landscapes

Empirical evidence is provided that within the inertial sublayer (i.e. logarithmic region) of adiabatic turbulent flows over smooth walls, the skewness of the vertical-velocity component $S_w$ displays universal behaviour, being a positive constant and constrained within the range $S_w \approx 0.1\unicode{x2013}0.16$ , regardless of flow configuration and Reynolds number. A theoretical model is then proposed to explain this behaviour, including the observed range of variations of $S_w$ . The proposed model clarifies why $S_w$ cannot be predicted from down-gradient closure approximations routinely employed in large-scale meteorological and climate models. The proposed model also offers an alternative and implementable approach for such large-scale models.

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The vertical-velocity skewness in the atmospheric boundary layer without buoyancy and Coriolis effects

Buono,

Katul,

Heisel

et al. 2024

Physics of Fluids

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One of the main features of near-neutral atmospheric boundary layer (ABL) turbulence is the positive vertical velocity skewness Skw above the roughness sublayer or the buffer region in smooth-walls. The Skw variations are receiving renewed interest in many climate-related parameterizations of the ABL given their significance to cloud formation and to testing sub-grid schemes for Large Eddy Simulations (LES). The vertical variations of Skw are explored here using wind tunnel and flume experiments collected above smooth, rough, and permeable-walls in the absence of buoyancy and Coriolis effects. These laboratory experiments form a necessary starting point to probe the canonical structure of Skw as they deal with a key limiting case (i.e., near-neutral conditions). Diagnostic models based on cumulant expansions, realizability constraints, and constant mass flux approach routinely employed in the convective boundary layer as well as prognostic models based on third-order budgets are used to explain variations in Skw for the idealized laboratory conditions. The failure of flux-gradient relations to model Skw from the gradients of the vertical velocity variance σw2 are explained and corrections based on models of energy transport offered. Novel links between the diagnostic and prognostic models are also featured, especially for the inertial term in the third-order budget of the vertical velocity fluctuation. The co-spectral properties of w′/σw vs w′2/σw2 are also presented for the first time to assess the dominant scales governing Skw in the inner and outer layers, where w′ is the fluctuating vertical velocity and σw is the vertical velocity standard deviation.

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Relationships Between Second and Third Moments in the Surface Layer Under Different Stratification over Grassland and Urban Landscapes

Cited by 7 publications

References 93 publications

Turbulence Characteristics in the Atmospheric Surface Layer Over a Heterogeneous Cultivated Surface in a Tropical Region

Turbulence Characteristics in the Atmospheric Surface Layer Over a Heterogeneous Cultivated Surface in a Tropical Region

The vertical-velocity skewness in the inertial sublayer of turbulent wall flows

The vertical-velocity skewness in the atmospheric boundary layer without buoyancy and Coriolis effects

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