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Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings

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A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Atmospheric Techniques, Instruments, and Modeling".

Deadline for manuscript submissions: closed (7 August 2020) | Viewed by 35212

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Dr. Domingo Muñoz-Esparza

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Guest Editor

Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
Interests: atmospheric boundary layers; multiscale modeling; large-eddy simulation; aviation turbulence; coupled atmosphere/wildfire phenomena; urban flows

Dr. Jeremy Sauer

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Guest Editor

Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
Interests: large-eddy simulation; atmospheric boundary layer turbulence; accelerated computing; transport and dispersion

Dr. Hyeyum (Hailey) Shin

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Guest Editor

Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
Interests: boundary-layer parameterizations; gray-zone physics; large-eddy simulation; multiscale atmospheric modeling

Special Issue Information

Dear Colleagues,

The atmospheric boundary layer (ABL) represents the lowest portion of the atmosphere, which is in direct contact with the Earth’s surface and where most of the activities impacting human lives take place. Advances in computational resources and computing technologies have recently begun to enable a more routine application of atmospheric models at turbulence-resolving grid spacings. There are, however, different approaches depending on the model’s grid spacing, which in turn dictates the turbulence closure. Beyond the mesoscale limit, traditional weather prediction models are being exercised at fine grid spacings that fall into the so-called ‘gray-zone’ of turbulence parameterization (~1 km < Δ < 100 m). This range of grid spacings requires scale-aware parameterizations that account for the nature of partially resolved turbulence and horizontal heterogeneity. On the high wavenumber end of the energy spectrum, large-eddy simulation (LES) models (Δ < 10 m) are used to explicitly represent production and part of the inertial range scales of three-dimensional turbulence. In this context, the application of the LES technique is no longer restricted to the classical idealized canonical scenarios and is experiencing a progressive transition toward large domain extents under heterogeneous forcing conditions that encompass part of the sub-meso and mesoscale spectrum. As a result, these methods are enabling unprecedented insight into complex ABL phenomena in realistic environments, yet imposing new modeling challenges. With this Special Issue, we aim to highlight recent progress in ABL modeling at turbulence-resolving scales, from new developments and methods to practical applications.

Articles on all aspects concerning turbulence-resolving modeling of ABLs are welcome, including but not restricted to the following areas:

LES forecasting;
Coupling of mesoscale and LES models;
Mesoscale modeling at under-resolved convection scales;
Gray-zone parameterizations;
Wildland fire phenomena;
Urban flows and pollutant dispersion;
Accelerated atmospheric models;
Fundamental turbulence phenomena;
Turbulence forecasts and UAVs;
Wind turbines and farms;
Complex terrain flows;
Wind-wave coupling for offshore ABLs;
Data assimilation techniques;
Stratified ABLs;
Boundary layer clouds.

Dr. Domingo Muñoz-Esparza
Dr. Jeremy Sauer
Dr. Hyeyum (Hailey) Shin
Guest Editors

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Published Papers (10 papers)

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Editorial

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3 pages, 167 KiB

Open AccessEditorial

Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings

by Domingo Muñoz-Esparza, Jeremy A. Sauer and Hyeyum Hailey Shin

Atmosphere 2020, 11(11), 1211; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11111211 - 10 Nov 2020

Viewed by 1532

Abstract

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

Research

Jump to: Editorial

28 pages, 5745 KiB

Open AccessArticle

Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain

by Alex Connolly, Leendert van Veen, James Neher, Bernard J. Geurts, Jeff Mirocha and Fotini Katopodes Chow

Atmosphere 2021, 12(1), 55; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos12010055 - 31 Dec 2020

Cited by 10 | Viewed by 2282

Abstract

A challenge to simulating turbulent flow in multiscale atmospheric applications is the efficient generation of resolved turbulence motions over an area of interest. One approach is to apply small perturbations to flow variables near the inflow planes of turbulence-resolving simulation domains nested within larger mesoscale domains. While this approach has been examined in numerous idealized and simple terrain cases, its efficacy in complex terrain environments has not yet been fully explored. Here, we examine the benefits of the stochastic cell perturbation method (CPM) over real complex terrain using data from the 2017 Perdigão field campaign, conducted in an approximately 2-km wide valley situated between two nearly parallel ridges. Following a typical configuration for multiscale simulation using nested domains within the Weather Research and Forecasting (WRF) model to downscale from the mesoscale to a large-eddy simulation (LES), we apply the CPM on a domain with horizontal grid spacing of 150 m. At this resolution, spurious coherent structures are often observed under unstable atmospheric conditions with moderate mean wind speeds. Results from such an intermediate resolution grid are often nested down for finer, more detailed LES, where these spurious structures adversely affect the development of turbulence on the subsequent finer grid nest. We therefore examine the impacts of the CPM on the representation of turbulence within the nested LES domain under moderate mean flow conditions in three different stability regimes: weakly convective, strongly convective, and weakly stable. In addition, two different resolutions of the underlying terrain are used to explore the role of the complex topography itself in generating turbulent structures. We demonstrate that the CPM improves the representation of turbulence within the LES domain, relative to the use of high-resolution complex terrain alone. During the convective conditions, the CPM improves the rate at which smaller-scales of turbulence form, while also accelerating the attenuation of the spurious numerically generated roll structures near the inflow boundary. During stable conditions, the coarse mesh spacing of the intermediate LES domain used herein was insufficient to maintain resolved turbulence using CPM as the flow develops downstream, highlighting the need for yet higher resolution under even weakly stable conditions, and the importance of accurate representation of flow on intermediate LES grids. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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19 pages, 3703 KiB

Open AccessArticle

WRF-LES Simulation of the Boundary Layer Turbulent Processes during the BLLAST Campaign

by Mireia Udina, Àlex Montornès, Pau Casso, Branko Kosović and Joan Bech

Atmosphere 2020, 11(11), 1149; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11111149 - 24 Oct 2020

Cited by 9 | Viewed by 6883

Abstract

A real case long-term nested large eddy simulation (LES) of 25-day duration is performed using the WRF-LES modelling system, with a maximum horizontal grid resolution of 111 m, in order to explore the ability of the model to reproduce the turbulence magnitudes within the first tens of metres of the boundary layer. Sonic anemometer measurements from a 60-m tower installed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign are used for verification, which is focused on the turbulent magnitudes in order to assess the success and limitations in resolving turbulent flow characteristics. The mesoscale and LES simulations reproduce the wind speed and direction fairly well, but only LES is able to reproduce the energy of eddies with lifetimes shorter than a few hours. The turbulent kinetic energy in LES simulation is generally underestimated during the daytime, mainly due to a vertical velocity standard deviation that is too low. The turbulent heat flux is misrepresented in the model, probably due to the inaccuracy of the sub-grid scheme. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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28 pages, 1051 KiB

Open AccessArticle

Resolution Dependence of Turbulent Structures in Convective Boundary Layer Simulations

by Mary-Jane M. Bopape, Robert S. Plant and Omduth Coceal

Atmosphere 2020, 11(9), 986; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11090986 - 15 Sep 2020

Cited by 5 | Viewed by 2364

Abstract

Large-eddy simulations are performed using the U.K. Met Office Large Eddy Model to study the effects of resolution on turbulent structures in a convective boundary layer. A standard Smagorinsky subgrid scheme is used. As the grid length is increased, the diagnosed height of the boundary layer increases, and the horizontally- and temporally-averaged temperature near the surface and in the inversion layer increase. At the highest resolution, quadrant analysis shows that the majority of events in the lower boundary layer are associated with cold descending air, followed by warm ascending air. The largest contribution to the total heat flux is made by warm ascending air, with associated strong thermals. At lower resolutions, the contribution to the heat flux from cold descending air is increased, and that from cold ascending air is reduced in the lower boundary layer; around the inversion layer, however, the contribution from cold ascending air is increased. Calculations of the heating rate show that the differences in cold ascending air are responsible for the warm bias below the boundary layer top in the low resolution simulations. Correlation length and time scales for coherent resolved structures increase with increasing grid coarseness. The results overall suggest that differences in the simulations are due to weaker mixing between thermals and their environment at lower resolutions. Some simple numerical experiments are performed to increase the mixing in the lower resolution simulations and to investigate backscatter. Such simulations are successful at reducing the contribution of cold ascending air to the heat flux just below the inversion, although the effects in the lower boundary layer are weaker. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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14 pages, 901 KiB

Open AccessArticle

Reconciling Chord Length Distributions and Area Distributions for Fields of Fractal Cumulus Clouds

by Nicholas R. Barron, Shawn D. Ryan and Thijs Heus

Atmosphere 2020, 11(8), 824; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11080824 - 05 Aug 2020

Cited by 8 | Viewed by 2816

Abstract

While the total cover of broken cloud fields can in principle be obtained from one-dimensional measurements, the cloud size distribution normally differs between two-dimensional (area) and one-dimensional retrieval (chord length) methods. In this study, we use output from high-resolution Large Eddy Simulations to generate a transfer function between the two. We retrieve chord lengths and areas for many clouds, and plot the one as a function of the other, and vice versa. We find that the cloud area distribution conditional on the chord length behaves like a gamma distribution with well-behaved parameters, with a mean

μ = 1.1 L

and a shape parameter

β = L^{- 0.645}

. Using this information, we are able to generate a transfer function that can adjust the chord length distribution so that it comes much closer to the cloud area distribution. Our transfer function improves the error in predicting the mean cloud size, and is performs without strong biases for smaller sample sizes. However, we find that the method is still has difficulties in accurately predicting the frequency of occurrence of the largest cloud sizes. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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13 pages, 36870 KiB

Open AccessArticle

Role of Wind Shear in the Decay of Convective Boundary Layers

by Seung-Bu Park, Jong-Jin Baik and Beom-Soon Han

Atmosphere 2020, 11(6), 622; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11060622 - 12 Jun 2020

Cited by 6 | Viewed by 2560

Abstract

The role of wind shear in the decay of the convective boundary layer (CBL) is systematically investigated using a series of large-eddy simulations. Nine CBLs with weak, intermediate, and strong wind shear are simulated, and their decays after stopping surface heat flux are investigated. After the surface heat flux is stopped, the boundary-layer-averaged turbulent kinetic energy (TKE) stays constant for almost one convective time scale and then decreases following a power law. While the decrease persists until the end of the simulation in the buoyancy-dominated (weak-shear) cases, the TKE in the other cases decreases slowly or even increases to a level which can be maintained by wind shear. In the buoyancy-dominated cases, convective cells occur, and they decay and oscillate over time. The oscillation of vertical velocity is not distinct in the other cases, possibly because wind shear disturbs the reversal of vertical circulations. The oscillations are detected again in the profiles of vertical turbulent heat flux in the buoyancy-dominated cases. In the strong-shear cases, mechanical turbulent eddies are generated, which transport heat downward in the lower boundary layers when convective turbulence decays significantly. The time series of vertical velocity skewness demonstrates the shear-dependent flow characteristics of decaying CBLs. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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16 pages, 11083 KiB

Open AccessArticle

Characteristics of Decaying Convective Boundary Layers Revealed by Large-Eddy Simulations

by Seung-Bu Park and Jong-Jin Baik

Atmosphere 2020, 11(4), 434; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11040434 - 24 Apr 2020

Cited by 7 | Viewed by 2909

Abstract

The decay of the Convective Boundary Layer (CBL) is studied using large-eddy simulations of free and advective CBLs, in which surface heat supply is suddenly cut off. After the cutoff, coherent convective circulations last about one convective time scale and then fade away. In the mixed layer, the decay time scale increases with height, indicating that nonlocal eddies decay slower than near-surface local eddies. The slower decay of turbulence in the middle of CBL than near-surface turbulence is reconfirmed from the analysis of pattern correlations of perturbations of vertical velocity. Perturbations of potential temperature and scalar concentration decay faster and slower than vertical velocity perturbations, respectively. A downward propagation of negative heat flux and its oscillation are found and a quadrant analysis reveals that warmer air sinking events are responsible for the downward propagation. The fourth quadrant events seem to be induced by demixing of air parcels, entrained from above the CBL. The advective CBL simulation with geostrophic wind illustrates that near-surface eddies are mechanically generated and they decelerate flow from the bottom up in the CBL/residual layer. The two-dimensional spectra show the height- and scale-dependent characteristics of decaying convective turbulence again in the free and advective boundary layer simulations. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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20 pages, 1880 KiB

Open AccessArticle

A Budget-Based Turbulence Length Scale Diagnostic

by Ivan Bašták Ďurán, Juerg Schmidli and Ritthik Bhattacharya

Atmosphere 2020, 11(4), 425; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11040425 - 22 Apr 2020

Cited by 10 | Viewed by 3198

Abstract

The most frequently used boundary-layer turbulence parameterization in numerical weather prediction (NWP) models are turbulence kinetic energy (TKE) based-based schemes. However, these parameterizations suffer from a potential weakness, namely the strong dependence on an ad-hoc quantity, the so-called turbulence length scale. The physical interpretation of the turbulence length scale is difficult and hence it cannot be directly related to measurements or large eddy simulation (LES) data. Consequently, formulations for the turbulence length scale in basically all TKE schemes are based on simplified assumptions and are model-dependent. A good reference for the independent evaluation of the turbulence length scale expression for NWP modeling is missing. Here we propose a new turbulence length scale diagnostic which can be used in the gray zone of turbulence without modifying the underlying TKE turbulence scheme. The new diagnostic is based on the TKE budget: The core idea is to encapsulate the sum of the molecular dissipation and the cross-scale TKE transfer into an effective dissipation, and associate it with the new turbulence length scale. This effective dissipation can then be calculated as a residuum in the TKE budget equation (for horizontal sub-domains of different sizes) using LES data. Estimation of the scale dependence of the diagnosed turbulence length scale using this novel method is presented for several idealized cases. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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19 pages, 30421 KiB

Open AccessArticle

Simulating Real Atmospheric Boundary Layers at Gray-Zone Resolutions: How Do Currently Available Turbulence Parameterizations Perform?

by Paula Doubrawa and Domingo Muñoz-Esparza

Atmosphere 2020, 11(4), 345; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11040345 - 31 Mar 2020

Cited by 31 | Viewed by 5028

Abstract

Recent computational and modeling advances have led a diverse modeling community to experiment with atmospheric boundary layer (ABL) simulations at subkilometer horizontal scales. Accurately parameterizing turbulence at these scales is a complex problem. The modeling solutions proposed to date are still in the development phase and remain largely unvalidated. This work assesses the performance of methods currently available in the Weather Research and Forecasting (WRF) model to represent ABL turbulence at a gray-zone grid spacing of 333 m. We consider three one-dimensional boundary layer parameterizations (MYNN, YSU and Shin-Hong) and coarse large-eddy simulations (LES). The reference dataset consists of five real-case simulations performed with WRF-LES nested down to 25 m. Results reveal that users should refrain from coarse LES and favor the scale-aware, Shin-Hong parameterization over traditional one-dimensional schemes. Overall, the spread in model performance is large for the cellular convection regime corresponding to the majority of our cases, with coarse LES overestimating turbulent energy across scales and YSU underestimating it and failing to reproduce its horizontal structure. Despite yielding the best results, the Shin-Hong scheme overestimates the effect of grid dependence on turbulent transport, highlighting the outstanding need for improved solutions to seamlessly parameterize turbulence across scales. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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17 pages, 1809 KiB

Open AccessCommunication

Multi-Scale Simulation of Wind Farm Performance during a Frontal Passage

by Robert S. Arthur, Jeffrey D. Mirocha, Nikola Marjanovic, Brian D. Hirth, John L. Schroeder, Sonia Wharton and Fotini K. Chow

Atmosphere 2020, 11(3), 245; https://0-doi-org.brum.beds.ac.uk/10.3390/atmos11030245 - 29 Feb 2020

Cited by 23 | Viewed by 4886

Abstract

Predicting the response of wind farms to changing flow conditions is necessary for optimal design and operation. In this work, simulation and analysis of a frontal passage through a utility scale wind farm is achieved for the first time using a seamless multi-scale modeling approach. A generalized actuator disk (GAD) wind turbine model is used to represent turbine–flow interaction, and results are compared to novel radar observations during the frontal passage. The Weather Research and Forecasting (WRF) model is employed with a nested grid setup that allows for coupling between multi-scale atmospheric conditions and turbine response. Starting with mesoscale forcing, the atmosphere is dynamically downscaled to the region of interest, where the interaction between turbulent flows and individual wind turbines is simulated with 10 m grid spacing. Several improvements are made to the GAD model to mimic realistic turbine operation, including a yawing capability and a power output calculation. Ultimately, the model is able to capture both the dynamics of the frontal passage and the turbine response; predictions show good agreement with observed background velocity, turbine wake structure, and power output after accounting for a phase shift in the mesoscale forcing. This study demonstrates the utility of the WRF-GAD model framework for simulating wind farm performance under complex atmospheric conditions. Full article

(This article belongs to the Special Issue Modeling of Atmospheric Boundary Layers at Turbulence-Resolving Grid Spacings)

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