scholarly journals Ventilation of a Mid-Size City under Stable Boundary Layer Conditions: A Simulation Using the LES Model PALM

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 401
Author(s):  
Jonathan Biehl ◽  
Bastian Paas ◽  
Otto Klemm
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Passive Scalar ◽  
City Center ◽  
Street Canyons ◽  
Stable Boundary ◽  
Northwest Germany ◽  
Stable Conditions ◽  
Les Model ◽  
The City

City centers have to cope with an increasing amount of air pollution. The supply of fresh air is crucial yet difficult to ensure, especially under stable conditions of the atmospheric boundary layer. This case study used the PArallelized Large eddy simulation (LES) Model PALM to investigate the wind field over an urban lake that had once been built as a designated fresh air corridor for the city center of Münster, northwest, Germany. The model initialization was performed using the main wind direction and stable boundary layer conditions as input. The initial wind and temperature profiles included a weak nocturnal low-level jet. By emitting a passive scalar at one point on top of a bridge, the dispersion of fresh air could be traced over the lake’s surface, within street canyons leading to the city center and within the urban boundary layer above. The concept of city ventilation was confirmed in principle, but the air took a direct route from the shore of the lake to the city center above a former river bed and its adjoining streets rather than through the street canyons. According to the dispersion of the passive scalar, half of the city center was supplied with fresh air originating from the lake. PALM proved to be a useful tool to study fresh air corridors under stable boundary layer conditions.

scholarly journals Turbulent Velocity-Variance Profiles in the Stable Boundary Layer Generated by a Nocturnal Low-Level Jet

2006 ◽  
Vol 63 (11) ◽  
pp. 2700-2719 ◽  
Author(s):  
Robert M. Banta ◽  
Yelena L. Pichugina ◽  
W. Alan Brewer
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Strong Wind ◽  
Surface Exchange ◽  
Stable Boundary ◽  
Low Level ◽  
Stable Conditions ◽  
Velocity Scale ◽  
Low Level Jet ◽  
Wind Profiles

Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind stable boundary layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was found to be 0.05, and 2) the three most common σ2u profile shapes were determined by stability (or Richardson number Ri). The least stable profile shapes had the maximum σ2u at the surface decreasing to a minimum at the height of the LLJ; profiles that were somewhat more stable had constant σ2u through a portion of the subjet layer; and the most stable of the profiles had a maximum of σ2u aloft, although it is important to note that the Ri for even the most stable of the three profile categories averaged less than 0.20. The datasets used in this study were two nights from the Cooperative Atmosphere–Surface Exchange Study 1999 campaign (CASES-99) and four nights from the Lamar Low-Level Jet Project, a wind-energy experiment in southeast Colorado, during September 2003.

scholarly journals The Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer Project (ISOBAR) —Unique fine-scale observations under stable and very stable conditions

2020 ◽  
pp. 1-64
Author(s):  
Stephan T. Kral ◽  
Joachim Reuder ◽  
Timo Vihma ◽  
Irene Suomi ◽  
Kristine Flacké Haualand ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Unmanned Aircraft ◽  
Unmanned Aircraft Systems ◽  
The Arctic ◽  
Fine Scale ◽  
Stable Boundary ◽  
Innovative Strategies ◽  
Aircraft Systems ◽  
Stable Conditions

Capsule summaryCombining ground-based micrometeorological instrumentation with boundary layer remote sensing and unmanned aircraft systems for high-resolution observations on the stable boundary layer over sea ice and corresponding modelling experiments.

scholarly journals Diagnostic Equations for the Stable Boundary Layer Height: Evaluation and Dimensional Analysis

2007 ◽  
Vol 46 (2) ◽  
pp. 212-225 ◽  
Author(s):  
G. J. Steeneveld ◽  
B. J. H. van de Wiel ◽  
A. A. M. Holtslag
Keyword(s):  
Boundary Layer ◽  
Dimensional Analysis ◽  
Stable Boundary Layer ◽  
Surface Friction ◽  
Coriolis Parameter ◽  
Layer Height ◽  
Stable Boundary ◽  
Boundary Layer Height ◽  
Stable Conditions ◽  
Surface Buoyancy

Abstract The performance of diagnostic equations for the stable boundary layer height h is evaluated with four observational datasets that represent a broad range of latitudes, land use, and surface roughness. In addition, large-eddy simulation results are used. Special care is given to data-quality selection. The diagnostic equations evaluated are so-called multilimit equations as derived by Zilitinkevich and coworkers in a number of papers. It appears that these equations show a serious negative bias, especially for h < 100 m, and it was found that the parameters involved could not be determined uniquely with calibration. As an alternative, dimensional analysis is used here to derive a formulation for h that is more robust. The formulation depends on the surface friction velocity u*, surface buoyancy flux Bs, Coriolis parameter, and the free-flow stability N. The relevance of the Coriolis parameter for the boundary layer height estimation in practice is also discussed. If the Coriolis parameter is ignored, two major regimes are found: h ∼ u*/N for weakly stable conditions and h ∼ (|Bs|/N 3)1/2 for moderate to very stable conditions.

scholarly journals High-Resolution In Situ Profiling through the Stable Boundary Layer: Examination of the SBL Top in Terms of Minimum Shear, Maximum Stratification, and Turbulence Decrease

2006 ◽  
Vol 63 (4) ◽  
pp. 1291-1307 ◽  
Author(s):  
B. B. Balsley ◽  
R. G. Frehlich ◽  
M. L. Jensen ◽  
Y. Meillier
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
High Resolution ◽  
Stable Boundary Layer ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Horizontal Wind ◽  
Small Scale ◽  
Stable Boundary ◽  
Stable Conditions

Abstract Some 50 separate high-resolution profiles of small-scale turbulence defined by the energy dissipation rate (ɛ), horizontal wind speed, and temperature from near the surface, through the nighttime stable boundary layer (SBL), and well into the residual layer are used to compare the various definitions of SBL height during nighttime stable conditions. These profiles were obtained during postmidnight periods on three separate nights using the Tethered Lifting System (TLS) during the Cooperative Atmosphere–Surface Exchange Study (CASES-99) campaign in east-central Kansas, October 1999. Although the number of profiles is insufficient to make any definitive conclusions, the results suggest that, under most conditions, the boundary layer top can be reasonably estimated in terms of a very significant decrease in the energy dissipation rate (i.e., the mixing height) with height. In the majority of instances this height lies slightly below the height of a pronounced minimum in wind shear and slightly above a maximum in N 2, where N is the Brunt–Väisälä frequency. When combined with flux measurements and vertical velocity variance data obtained from the nearby 55-m tower, the results provide additional insights into SBL processes, even when the boundary layer, by any definition, extends to heights well above the top of the tower. Both the TLS profiles and tower data are then used for preliminary high-resolution studies into various categories of SBL structure, including the so-called upside-down boundary layer.

scholarly journals Implementation in the NCEP GFS of a Hybrid Eddy-Diffusivity Mass-Flux (EDMF) Boundary Layer Parameterization with Dissipative Heating and Modified Stable Boundary Layer Mixing

2016 ◽  
Vol 31 (1) ◽  
pp. 341-352 ◽  
Author(s):  
Jongil Han ◽  
Marcin L. Witek ◽  
Joao Teixeira ◽  
Ruiyu Sun ◽  
Hua-Lu Pan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Stable Boundary Layer ◽  
Eddy Diffusivity ◽  
Dissipative Heating ◽  
Tropical Ocean ◽  
Medium Range Weather Forecast ◽  
Stable Boundary ◽  
Stable Conditions ◽  
Pbl Scheme

Abstract The current operational eddy-diffusivity countergradient (EDCG) planetary boundary layer (PBL) scheme in the NCEP Global Forecast System (GFS) tends to underestimate the PBL growth in the convective boundary layer (CBL). To improve CBL growth, an eddy-diffusivity mass-flux (EDMF) PBL scheme is developed, where the nonlocal transport by large turbulent eddies is represented by a mass-flux (MF) scheme and the local transport by small eddies is represented by an eddy-diffusivity (ED) scheme. For the vertical momentum mixing, the MF scheme is modified to include the effect of the updraft-induced pressure gradient force. While the EDMF scheme displays better CBL growth than the EDCG scheme, it tends to overproduce the amount of low clouds and degrades wind vector forecasts over the tropical ocean where strongly unstable PBLs are rarely found. In order not to degrade the forecast skill in the tropics, a hybrid scheme is developed, where the EDMF scheme is applied only for the strongly unstable PBL, while the EDCG scheme is used for the weakly unstable PBL. Along with the hybrid EDMF scheme, the heating by turbulent kinetic energy (TKE) dissipation is parameterized to reduce an energy imbalance in the GFS. To enhance a too weak vertical turbulent mixing for weakly and moderately stable conditions, the current local scheme in the stable boundary layer (SBL) is modified to use an eddy-diffusivity profile method. The hybrid EDMF PBL scheme with TKE dissipative heating and modified SBL mixing led to significant improvements in some key medium-range weather forecast metrics and was operationally implemented into the NCEP GFS in January 2015.

Similarity Theory, Intermittency and Turbulences in the Stable Boundary Layer

2005 ◽  
Vol 277-279 ◽  
pp. 618-624 ◽  
Author(s):  
Kyungm Ja Ha ◽  
Kyung Eak Kim ◽  
Yu Kyung Hyun ◽  
Eun Hee Jeon ◽  
Larry Mahrt
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Similarity Theory ◽  
Similarity Relation ◽  
Stability Parameters ◽  
Stable Boundary ◽  
Flux Gradient ◽  
Stable Conditions ◽  
New Treatments ◽  
Theory Z

The evaluation of similarity theory, z-less formulation of turbulence, and validation for various stable conditions is addressed with the use of CASES99 data over grassland. The dependence of the flux-gradient relationships on height and stability parameters is evaluated. For very stable conditions, similarity relation based on Monin-Obukhov theory is locally invalid and new treatments are required. The flux intermittency is recommended as a good indicator of stability for very thin stable boundary layer.

scholarly journals Thermal Submeso Motions in the Nocturnal Stable Boundary Layer. Part 2: Generating Mechanisms and Implications

2021 ◽  
Author(s):  
Lena Pfister ◽  
Karl Lapo ◽  
Larry Mahrt ◽  
Christoph K. Thomas
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Side Wall ◽  
Cold Pool ◽  
Continuous Data ◽  
Valley Bottom ◽  
Near Surface ◽  
Cold Air ◽  
Stable Boundary ◽  
Surface Temperatures

AbstractIn the stable boundary layer, thermal submesofronts (TSFs) are detected during the Shallow Cold Pool experiment in the Colorado plains, Colorado, USA in 2012. The topography induces TSFs by forming two different air layers converging on the valley-side wall while being stacked vertically above the valley bottom. The warm-air layer is mechanically generated by lee turbulence that consistently elevates near-surface temperatures, while the cold-air layer is thermodynamically driven by radiative cooling and the corresponding cold-air drainage decreases near-surface temperatures. The semi-stationary TSFs can only be detected, tracked, and investigated in detail when using fibre-optic distributed sensing (FODS), as point observations miss TSFs most of the time. Neither the occurrence of TSFs nor the characteristics of each air layer are connected to a specific wind or thermal regime. However, each air layer is characterized by a specific relationship between the wind speed and the friction velocity. Accordingly, a single threshold separating different flow regimes within the boundary layer is an oversimplification, especially during the occurrence of TSFs. No local forcings or their combination could predict the occurrence of TSFs except that they are less likely to occur during stronger near-surface or synoptic-scale flow. While classical conceptualizations and techniques of the boundary layer fail in describing the formation of TSFs, the use of spatially continuous data obtained from FODS provide new insights. Future studies need to incorporate spatially continuous data in the horizontal and vertical planes, in addition to classic sensor networks of sonic anemometry and thermohygrometers to fully characterize and describe boundary-layer phenomena.

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