scholarly journals ANÁLISE DA PERFORMANCE DE UM MODELO DE COLUNA SIMPLES UTILIZANDO DIFERENTES PARAMETRIZAÇÕES PARA A TAXA DISSIPAÇÃO VISCOSA DE ENERGIA CINÉTICA TURBULENTA

2016 ◽  
Vol 38 ◽  
pp. 394
Author(s):  
Janete Gonçalves Lira ◽  
Eduardo Stüker ◽  
Jean Jonathan Schuster ◽  
Cristiano Henrique Schuster ◽  
Daniel Michelon dos Santos ◽  
...  
Keyword(s):  
Numerical Models ◽  
Atmospheric Flow ◽  
Stable Regime ◽  
Stable Conditions ◽  
Single Column ◽  
Weather And Climate ◽  
Single Column Model ◽  
Stable Atmospheric Boundary Layer ◽  
Weakly Stable ◽  
Turbulence Formulations

The proper description of the atmospheric flow in the stable atmospheric boundary layer is one of the most complex tasks to be performed by numerical models of weather and climate prediction. Most of the parameterizations used in these models are based on the statistical theory of turbulence in their conception. However, this theory is valid only for a flow in which turbulence is homogeneous, isotropic and stationary, a conditions that are not commonly found overnight. Basically, the nighttime flow can be classified in two major regimes: very stable, where turbulence is almost entirely suppressed; and weakly stable regime, with intense turbulent mixing. The transition between these regimes is known as atmospheric coupling, and it can happens a lot of times along the same night. In this work, we implemented a single column model with turbulence closure 1.5, in three different configurations and three different turbulence formulations. In general, the model results show that, all the configurations are able to reproduce the average characteristics of the flow in the weakly stable conditions.

Turbulence and Vertical Fluxes in the Stable Atmospheric Boundary Layer. Part II: A Novel Mixing-Length Model

2013 ◽  
Vol 70 (6) ◽  
pp. 1528-1542 ◽  
Author(s):  
Jing Huang ◽  
Elie Bou-Zeid ◽  
Jean-Christophe Golaz
Keyword(s):  
Large Eddy Simulations ◽  
Mixing Length ◽  
New Model ◽  
Vertical Fluxes ◽  
Stable Conditions ◽  
Large Eddy ◽  
Single Column ◽  
Single Column Model ◽  
Stable Atmospheric Boundary Layer ◽  
Neutral Conditions

Abstract This is the second part of a study about turbulence and vertical fluxes in the stable atmospheric boundary layer. Based on a suite of large-eddy simulations in Part I where the effects of stability on the turbulent structures and kinetic energy are investigated, first-order parameterization schemes are assessed and tested in the Geophysical Fluid Dynamics Laboratory (GFDL)’s single-column model. The applicability of the gradient-flux hypothesis is first examined and it is found that stable conditions are favorable for that hypothesis. However, the concept of introducing a stability correction function fm as a multiplicative factor into the mixing length used under neutral conditions lN is shown to be problematic because fm computed a priori from large-eddy simulations tends not to be a universal function of stability. With this observation, a novel mixing-length model is proposed, which conforms to large-eddy simulation results much better under stable conditions and converges to the classic model under neutral conditions. Test cases imposing steady as well as unsteady forcings are developed to evaluate the performance of the new model. It is found that the new model exhibits robust performance as the stability strength is changed, while other models are sensitive to changes in stability. For cases with unsteady forcings, which are very rarely simulated or tested, the results of the single-column model and large-eddy simulations are also closer when the new model is used, compared to the other models. However, unsteady cases are much more challenging for the turbulence closure formulations than cases with steady surface forcing.

A Simple, Efficient Solution of Flux–Profile Relationships in the Atmospheric Surface Layer

2006 ◽  
Vol 45 (2) ◽  
pp. 341-347 ◽  
Author(s):  
Jonathan E. Pleim
Keyword(s):  
Surface Layer ◽  
Numerical Models ◽  
Iterative Solution ◽  
State Variables ◽  
Simple Scheme ◽  
Meteorological Model ◽  
Stable Regime ◽  
Stability Functions ◽  
Stable Conditions ◽  
Aerodynamic Roughness

Abstract This note describes a simple scheme for analytical estimation of the surface-layer similarity functions from state variables. What distinguishes this note from the many previous papers on this topic is that this method is specifically targeted for numerical models in which simplicity and economic execution are critical. In addition, it has been in use in a mesoscale meteorological model for several years. For stable conditions, a very simple scheme is presented that compares well to the iterative solution. The stable scheme includes a very stable regime in which the slope of the stability functions is reduced to permit significant fluxes to occur, which is particularly important for numerical models in which decoupling from the surface can be an important problem. For unstable conditions, simple schemes generalized for varying ratios of aerodynamic roughness to thermal roughness (z0/z0h) are less satisfactory. Therefore, a simple scheme has been empirically derived for a fixed z0/z0h ratio, which represents quasi-laminar sublayer resistance.

scholarly journals Continuous Single-Column Model Evaluation at a Permanent Meteorological Supersite

2012 ◽  
Vol 93 (9) ◽  
pp. 1389-1400 ◽  
Author(s):  
R. A. J. Neggers ◽  
A. P. Siebesma ◽  
T. Heus
Keyword(s):  
Case Studies ◽  
General Circulation ◽  
Column Model ◽  
Parameterization Schemes ◽  
Numerical Predictions ◽  
Single Column ◽  
Weather And Climate ◽  
Single Column Model ◽  
Process Level

Uncertainties in numerical predictions of weather and climate are often linked to the representation of unresolved processes that act relatively quickly compared to the resolved general circulation. These processes include turbulence, convection, clouds, and radiation. Single-column model (SCM) simulation of idealized cases and the subsequent evaluation against large-eddy simulation (LES) results has become an often used and relied on method to obtain insight at process level into the behavior of such parameterization schemes; benefits of SCM simulation are the enhanced model transparency and the high computational efficiency. Although this approach has achieved demonstrable success, some shortcomings have been identified; among these, i) the statistical significance and relevance of single idealized case studies might be questioned and ii) the use of observational datasets has been relatively limited. A recently initiated project named the Royal Netherlands Meteorological Institute (KNMI) Parameterization Testbed (KPT) is part of a general move toward a more statistically significant process-level evaluation, with the purpose of optimizing the identification of problems in general circulation models that are related to parameterization schemes. The main strategy of KPT is to apply continuous long-term SCM simulation and LES at various permanent meteorological sites, in combination with comprehensive evaluation against observations at multiple time scales. We argue that this strategy enables the reproduction of typical long-term mean behavior of fast physics in large-scale models, but it still preserves the benefits of single-case studies (such as model transparency). This facilitates the tracing and understanding of errors in parameterization schemes, which should eventually lead to a reduction of related uncertainties in numerical predictions of weather and climate.

scholarly journals Nighttime wind and scalar variability within and above an Amazonian canopy

2018 ◽  
Vol 18 (5) ◽  
pp. 3083-3099 ◽  
Author(s):  
Pablo E. S. Oliveira ◽  
Otávio C. Acevedo ◽  
Matthias Sörgel ◽  
Anywhere Tsokankunku ◽  
Stefan Wolff ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Amazon Forest ◽  
Stable Regime ◽  
Stable Conditions ◽  
Weakly Stable ◽  
The Stability ◽  
The Relationship ◽  
Temporal Windows ◽  
Scalar Variability

Abstract. Nocturnal turbulent kinetic energy (TKE) and fluxes of energy, CO2 and O3 between the Amazon forest and the atmosphere are evaluated for a 20-day campaign at the Amazon Tall Tower Observatory (ATTO) site. The distinction of these quantities between fully turbulent (weakly stable) and intermittent (very stable) nights is discussed. Spectral analysis indicates that low-frequency, nonturbulent fluctuations are responsible for a large portion of the variability observed on intermittent nights. In these conditions, the low-frequency exchange may dominate over the turbulent transfer. In particular, we show that within the canopy most of the exchange of CO2 and H2O happens on temporal scales longer than 100 s. At 80 m, on the other hand, the turbulent fluxes are almost absent in such very stable conditions, suggesting a boundary layer shallower than 80 m. The relationship between TKE and mean winds shows that the stable boundary layer switches from the very stable to the weakly stable regime during intermittent bursts of turbulence. In general, fluxes estimated with long temporal windows that account for low-frequency effects are more dependent on the stability over a deeper layer above the forest than they are on the stability between the top of the canopy and its interior, suggesting that low-frequency processes are controlled over a deeper layer above the forest.

Micrometeorological Aspects of Spraying within a Surface Inversion.

2021 ◽  
Author(s):  
Warwick Grace ◽  
Graeme Tepper
Keyword(s):  
Heat Flux ◽  
Turbulent Mixing ◽  
Long Distance ◽  
Maximum Heat ◽  
Stable Case ◽  
Stable Regime ◽  
Stable Conditions ◽  
Order Of Magnitude ◽  
Weakly Stable ◽  
High Concentrations

AbstractPesticide applications during surface inversions can lead to spray drift causing severe damage up to several kilometers off-target. Current regulations in Australia prohibit spray application of certain agricultural chemicals when hazardous surface inversions exist. This severely limits spray opportunities.Surface inversions can be classified as weakly or strongly stable. In the weakly stable case, moderate to strong turbulent mixing is not supportive of long-distance concentrated drift. In the very stable case, weak turbulent mixing can support the transport of high concentrations of fine material over long distances. A review of the literature and our analyses indicate that if the turbulence, as measured by the standard deviation of the vertical wind speed σw, is greater than about 0.2 m/s then turbulence-driven mixing and dispersion is moderate to strong and conversely if σw is less than about 0.2 m/s then turbulence-driven mixing and dispersion is weaker (an order of magnitude). The concept of maximum downward heat flux as a natural division between the regimes is applied within Monin-Obukhov Stability Theory and it is shown that the observed mean σw of 0.2 m/s aligns with the ridge line of maximum heat flux in stable conditions. The level of turbulence in the weakly stable regime is comparable to the turbulence typically observed in near-neutral conditions which are recommended under current guidelines as suitable for spraying and is therefore seen as an acceptable prerequisite to avoid non-dispersive spraying conditions.

scholarly journals The Extrapolation of Near-Surface Wind Speeds under Stable Stratification Using an Equilibrium-Based Single-Column Model Approach

2016 ◽  
Vol 55 (4) ◽  
pp. 923-943 ◽  
Author(s):  
Michael Optis ◽  
Adam Monahan
Keyword(s):  
Wind Profile ◽  
Stable Stratification ◽  
Internal Boundary ◽  
Near Surface ◽  
Column Model ◽  
Wind Speeds ◽  
Stable Conditions ◽  
Single Column ◽  
Equilibrium Approach ◽  
Single Column Model

AbstractClassical approaches to modeling the near-surface (i.e., below 200 m) wind profile are equilibrium based (i.e., no time evolution) and either lack a physical basis or are based on surface-layer physics. In this study, the limits of the equilibrium approach in stable stratification are further tested by applying the method within a more physically comprehensive single-column model (SCM) framework. The SCM considered here is a highly idealized momentum and temperature budget model that uses a range of different parameterizations of turbulent fluxes. A 10-yr observational dataset obtained from the 213-m Cabauw tower in the Netherlands is used to drive the SCM and to assess model performance. Results from this study demonstrate several limitations of this SCM-based equilibrium approach. The existence of two physically meaningful equilibrium solutions for a given value of the surface turbulent temperature flux (used as a lower boundary in the SCM) generally results in either a tendency to underestimate stratification or the breakdown of the model because of runaway cooling and collapsed turbulence. Different representations of the geostrophic wind profile accounting for baroclinic effects caused by the strong land–sea temperature gradient at Cabauw are shown to have only a modest influence on the mean wind profile. The local internal boundary layer (IBL) at Cabauw results in a strong tendency for the SCM to overestimate wind speeds in weakly to moderately stable conditions. In very stable conditions (where the IBL influence was low), the equilibrium approach remained limited because of its inability to account for time-evolving phenomena such as the inertial oscillation and the low-level jet.

Engaging the Community in the Development of Physics for NWP Models

2020 ◽  
Author(s):  
Ligia Bernardet ◽  
Grant Firl ◽  
Dom Heinzeller ◽  
Laurie Carson ◽  
Xia Sun ◽  
...  
Keyword(s):  
Case Studies ◽  
Numerical Models ◽  
Weather Prediction ◽  
Forecast System ◽  
Linear Processes ◽  
Column Model ◽  
Model Code ◽  
Single Column ◽  
Single Column Model ◽  
The U.S

<p>Contributions from the community (national laboratories, universities, and private companies) have the potential to improve operational numerical models and translate to better forecasts. However, researchers often have difficulty learning about the most pressing forecast biases that need to be addressed, running operational models, and funneling their developments onto the research-to-operations process. Common impediments are lack of access to current and portable model code, insufficient documentation and support, difficulty in finding information about forecast shortcomings and systematic errors, and unclear processes to contribute code back to operational centers. </p><p>The U.S. Developmental Testbed Center (DTC) has the mission of connecting the research and operational Numerical Weather Prediction (NWP) communities. Specifically in the field of model physics, the DTC works on several fronts to foster the engagement of community developers with the Unified Forecast System (UFS) employed by the U.S. National Oceanic and Atmospheric Administration (NOAA).  As a foundational step, the UFS’ operational and developmental physical parameterizations and suites are now publicly distributed through the Common Community Physics Package (CCPP), a library of physics schemes and associated framework that enables their use with various models. The CCPP can be used for physics experimentation and development in a hierarchical fashion, with hosts ranging in complexity from a single-column model driven by experimental case studies to fully coupled Earth system models. This hierarchical capability facilitates the isolation of non-linear processes prior to their integration in complex systems. </p><p>The first public release of a NOAA Unified Forecast System (UFS) application is expected for February 2020, with a focus on the Medium-Range Weather Application. This global configuration uses the CCPP and will be documented and supported to the community. To accompany future public releases, the DTC is creating a catalog of case studies to exemplify the most prominent model biases identified by the US National Weather Service. The case studies will be made available to the community, who will be able to rerun the cases, to test their innovations and document model improvements. </p><p>In this poster we will summarize how we are using the UFS public release, the single-column model, the CCPP, and the incipient catalog of code studies to create stronger connections among the groups that diagnose, develop, and produce predictions using physics suites.</p>

scholarly journals Turbulent and non-turbulent exchange of scalars between the forest and the atmosphere at night in Amazonia

2017 ◽  
Author(s):  
Pablo E. S. Oliveira ◽  
Otávio C. Acevedo ◽  
Matthias Sörgel ◽  
Anywhere Tsokankunku ◽  
Stefan Wolff ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Amazon Forest ◽  
Turbulent Transfer ◽  
Stable Regime ◽  
Stable Conditions ◽  
Weakly Stable ◽  
The Stability ◽  
The Relationship ◽  
Temporal Windows

Abstract. Nocturnal turbulent kinetic energy (TKE) and fluxes of energy, CO2 and O3 between the Amazon forest and the atmosphere are evaluated for a 20-day campaign at the Amazon Tall Tower Observatory (ATTO) site. The distinction of these quantities between fully turbulent (weakly stable) and intermittent (very stable) nights is discussed. Spectral analysis indicates that low-frequency, non-turbulent fluctuations are responsible for a large portion of the variability observed on intermittent nights. In these conditions, the low-frequency exchange may dominate over the turbulent transfer. In particular, we show that within the canopy most of the exchange of CO2 and H2O happens on temporal scales longer than 100 s. At 80 m, on the other hand, the turbulent fluxes are almost absent in such very stable conditions, suggesting a boundary layer shallower than 80 m. The relationship between TKE and mean winds shows that the stable boundary layer switches from the very stable to the weakly stable regime during intermittent bursts of turbulence. In general, fluxes estimated with long temporal windows that account for the low-frequency effects are more dependent on the stability over a deeper layer above the forest than they are on the stability between the top of the canopy and its interior, suggesting that low-frequency processes are controlled over a deeper layer above the forest.

On modelling physical systems with stochastic models: diffusion versus Lévy processes

2008 ◽  
Vol 366 (1875) ◽  
pp. 2455-2474 ◽  
Author(s):  
Cécile Penland ◽  
Brian D Ewald
Keyword(s):  
Differential Equations ◽  
Stochastic Models ◽  
Lévy Processes ◽  
Numerical Models ◽  
Gaussian White Noise ◽  
Levy Processes ◽  
Physical Systems ◽  
Random Forcing ◽  
Weather And Climate ◽  
Made In

Stochastic descriptions of multiscale interactions are more and more frequently found in numerical models of weather and climate. These descriptions are often made in terms of differential equations with random forcing components. In this article, we review the basic properties of stochastic differential equations driven by classical Gaussian white noise and compare with systems described by stable Lévy processes. We also discuss aspects of numerically generating these processes.

scholarly journals Saharan dust and giant quartz particle transport towards Iceland

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
György Varga ◽  
Pavla Dagsson-Walhauserová ◽  
Fruzsina Gresina ◽  
Agusta Helgadottir
Keyword(s):  
Numerical Models ◽  
Saharan Dust ◽  
Atmospheric Environment ◽  
The Arctic ◽  
Dust Particles ◽  
Atmospheric Flow ◽  
Dust Transport ◽  
Strong Winds ◽  
Dust Events ◽  
Local Dust

AbstractMineral dust emissions from Saharan sources have an impact on the atmospheric environment and sedimentary units in distant regions. Here, we present the first systematic observations of long-range Saharan dust transport towards Iceland. Fifteen Saharan dust episodes were identified to have occurred between 2008 and 2020 based on aerosol optical depth data, backward trajectories and numerical models. Icelandic samples from the local dust sources were compared with deposited dust from two severe Saharan dust events in terms of their granulometric and mineralogical characteristics. The episodes were associated with enhanced meridional atmospheric flow patterns driven by unusual meandering jets. Strong winds were able to carry large Saharan quartz particles (> 100 µm) towards Iceland. Our results confirm the atmospheric pathways of Saharan dust towards the Arctic, and identify new northward meridional long-ranged transport of giant dust particles from the Sahara, including the first evidence of their deposition in Iceland as previously predicted by models.

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