scholarly journals Implementation and evaluation of a unified turbulence parameterization throughout the canopy and roughness sublayer in Noah‐MP snow simulations

2021 ◽  
Author(s):  
Ronnie Abolafia‐Rosenzweig ◽  
Cenlin He ◽  
Sean Burns ◽  
Fei Chen
Keyword(s):  
Roughness Sublayer ◽  
Turbulence Parameterization

Influence of Canopy Seasonal Changes on Turbulence Parameterization within the Roughness Sublayer over an Orchard Canopy

2016 ◽  
Vol 55 (6) ◽  
pp. 1391-1407 ◽  
Author(s):  
M. Shapkalijevski ◽  
A. F. Moene ◽  
H. G. Ouwersloot ◽  
E. G. Patton ◽  
J. Vilà-Guerau de Arellano
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Turbulent Exchange ◽  
Roughness Sublayer ◽  
Atmospheric Conditions ◽  
Exchange Coefficient ◽  
Turbulence Parameterization ◽  
Velocity Variances ◽  
Neutral Conditions ◽  
Turbulent Exchange Coefficient

Abstract In this observational study, the role of tree phenology on the atmospheric turbulence parameterization over 10-m-tall and relatively sparse deciduous vegetation is quantified. Observations from the Canopy Horizontal Array Turbulence Study (CHATS) field experiment are analyzed to establish the dependence of the turbulent exchange of momentum, heat, and moisture, as well as kinetic energy on canopy phenological evolution through widely used parameterization models based on 1) dimensionless gradients or 2) turbulent kinetic energy (TKE) in the roughness sublayer. Observed vertical turbulent fluxes and gradients of mean wind, temperature, and humidity, as well as velocity variances, are used in combination with empirical dimensionless functions to calculate the turbulent exchange coefficient. The analysis shows that changes in canopy phenology influence the turbulent exchange of all quantities analyzed in this study. The turbulent exchange coefficients of those quantities are twice as large near the canopy top for a leafless canopy than for a full-leaf canopy under unstable and near-neutral conditions. This turbulent exchange coefficient difference is related to the differing penetration depths of the turbulent eddies organized at the canopy top, which increase for a canopy without leaves. The TKE and dissipation analysis under near-neutral atmospheric conditions additionally shows that TKE exchange increases for a leafless canopy because of reduced TKE dissipation efficiency relative to that when the canopy is in full-leaf stage. The study closes with discussion surrounding the implications of these findings for parameterizations used in large-scale models.

scholarly journals Urban Boundary Layers Over Dense and Tall Canopies

2021 ◽  
Author(s):  
Alexandros Makedonas ◽  
Matteo Carpentieri ◽  
Marco Placidi
Keyword(s):  
Packing Density ◽  
Laser Doppler Anemometry ◽  
Canopy Height ◽  
Roughness Sublayer ◽  
Average Height ◽  
Wind Tunnel Experiments ◽  
Mean Velocity ◽  
Flow Features ◽  
Stress Layer ◽  
Density Results

AbstractWind-tunnel experiments were carried out on four urban morphologies: two tall canopies with uniform height and two super-tall canopies with a large variation in element heights (where the maximum element height is more than double the average canopy height, $$h_{max}=2.5h_{avg}$$ h max = 2.5 h avg ). The average canopy height and packing density are fixed across the surfaces to $$h_{avg} = 80~\hbox {mm}$$ h avg = 80 mm , and $$\lambda _{p} = 0.44$$ λ p = 0.44 , respectively. A combination of laser Doppler anemometry and direct-drag measurements are used to calculate and scale the mean velocity profiles with the boundary-layer depth $$\delta $$ δ . In the uniform-height experiment, the high packing density results in a ‘skimming flow’ regime with very little flow penetration into the canopy. This leads to a surprisingly shallow roughness sublayer (depth $$\approx 1.15h_{avg}$$ ≈ 1.15 h avg ), and a well-defined inertial sublayer above it. In the heterogeneous-height canopies, despite the same packing density and average height, the flow features are significantly different. The height heterogeneity enhances mixing, thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer is found to exist extending up to just above the tallest element height (corresponding to $$z/h_{avg} = 2.85$$ z / h avg = 2.85 ), which is found to be the dominant length scale controlling the flow behaviour. Results point toward the existence of a constant-stress layer for all surfaces considered herein despite the severity of the surface roughness ($$\delta /h_{avg} = 3 - 6.25$$ δ / h avg = 3 - 6.25 ). This contrasts with the previous literature.

Sweeping Effects Modify Taylor’s Frozen Turbulence Hypothesis for Scalars in the Roughness Sublayer

2021 ◽  
Author(s):  
K. A. Everard ◽  
G. G. Katul ◽  
G. A. Lawrence ◽  
A. Christen ◽  
M. B. Parlange
Keyword(s):  
Roughness Sublayer

Counter-Gradient Term Applied to the Turbulence Parameterization in the BRAMS

2017 ◽  
pp. 299-309
Author(s):  
M. E. S. Welter ◽  
H. F. de Campos Velho ◽  
S. R. Freitas ◽  
R. S. R. Ruiz
Keyword(s):  
Gradient Term ◽  
Turbulence Parameterization

scholarly journals Effects of Vegetation and Topography on the Boundary Layer Structure above the Amazon Forest

2020 ◽  
Vol 77 (8) ◽  
pp. 2941-2957
Author(s):  
Marcelo Chamecki ◽  
Livia S. Freire ◽  
Nelson L. Dias ◽  
Bicheng Chen ◽  
Cléo Quaresma Dias-Junior ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Phase Space ◽  
Vertical Structure ◽  
Layer Structure ◽  
Roughness Sublayer ◽  
Large Contribution ◽  
Amazon Forest ◽  
Two Dimensional ◽  
Dimensional Phase Space ◽  
Field Campaigns

Abstract Observational data from two field campaigns in the Amazon forest were used to study the vertical structure of turbulence above the forest. The analysis was performed using the reduced turbulent kinetic energy (TKE) budget and its associated two-dimensional phase space. Results revealed the existence of two regions within the roughness sublayer in which the TKE budget cannot be explained by the canonical flat-terrain TKE budgets in the canopy roughness sublayer or in the lower portion of the convective ABL. Data analysis also suggested that deviations from horizontal homogeneity have a large contribution to the TKE budget. Results from LES of a model canopy over idealized topography presented similar features, leading to the conclusion that flow distortions caused by topography are responsible for the observed features in the TKE budget. These results support the conclusion that the boundary layer above the Amazon forest is strongly impacted by the gentle topography underneath.

scholarly journals Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0)

2017 ◽  
Author(s):  
Gordon B. Bonan ◽  
Edward G. Patton ◽  
Ian N. Harman ◽  
Keith W. Oleson ◽  
John J. Finnigan ◽  
...  
Keyword(s):  
Heat Flux ◽  
Friction Velocity ◽  
Sensible Heat Flux ◽  
Roughness Sublayer ◽  
Sensible Heat ◽  
Area Index ◽  
Community Land Model ◽  
Diurnal Range ◽  
Radiative Temperature ◽  
Canopy Model

Abstract. Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multi-layer canopy model (CLM-ml v0) test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at 7 forest, 2 grassland, and 3 cropland AmeriFlux sites over a range of canopy height, leaf area index, and climate. The CLM4.5 has pronounced biases during summer months at forest sites in mid-day latent heat flux, sensible heat flux, and gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. The signature of the roughness sublayer is most evident in sensible heat flux, friction velocity, and the diurnal cycle of radiative temperature. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin–Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these short canopies. The multi-layer canopy with the roughness sublayer turbulence improves simulations compared with the CLM4.5 while also advancing the theoretical basis for surface flux parameterizations.

scholarly journals The Atmospheric Boundary Layer Over Urban-Like Terrain: Influence of the Plan Density on Roughness Sublayer Dynamics

2018 ◽  
Vol 170 (2) ◽  
pp. 205-234 ◽  
Author(s):  
Laurent Perret ◽  
Jérémy Basley ◽  
Romain Mathis ◽  
Thibaud Piquet
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Roughness Sublayer

scholarly journals Structure of high Reynolds number boundary layers over cube canopies

2019 ◽  
Vol 870 ◽  
pp. 460-491 ◽  
Author(s):  
Jérémy Basley ◽  
Laurent Perret ◽  
Romain Mathis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Coherent Structures ◽  
High Reynolds Number ◽  
Stereoscopic Particle Image Velocimetry ◽  
Roughness Sublayer ◽  
Large Field ◽  
Normal Velocity ◽  
High Reynolds

The influence of a cube-based canopy on coherent structures of the flow was investigated in a high Reynolds number boundary layer (thickness $\unicode[STIX]{x1D6FF}\sim 30\,000$ wall units). Wind tunnel experiments were conducted considering wall configurations that represent three idealised urban terrains. Stereoscopic particle image velocimetry was employed using a large field of view in a streamwise–spanwise plane ($0.55\unicode[STIX]{x1D6FF}\times 0.5\unicode[STIX]{x1D6FF}$) combined to two-point hot-wire measurements. The analysis of the flow within the inertial layer highlights the independence of its characteristics from the wall configuration. The population of coherent structures is in agreement with that of smooth-wall boundary layers, i.e. consisting of large- and very-large-scale motions, sweeps and ejections, as well as smaller-scale vortical structures. The characteristics of vortices appear to be independent of the roughness configuration while their spatial distribution is closely linked to large meandering motions of the boundary layer. The canopy geometry only significantly impacts the wall-normal exchanges within the roughness sublayer. Bi-dimensional spectral analysis demonstrates that wall-normal velocity fluctuations are constrained by the presence of the canopy for the densest investigated configurations. This threshold in plan area density above which large scales from the overlying boundary layer can penetrate the roughness sublayer is consistent with the change of the flow regime reported in the literature and constitutes a major difference with flows over vegetation canopies.

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