scholarly journals A Cumulus Cloud Microphysics Parameterization for Cloud-Resolving Models

2013 ◽  
Vol 70 (5) ◽  
pp. 1423-1436 ◽  
Author(s):  
Yefim Kogan
Keyword(s):  
Boundary Layer ◽  
Cloud Microphysics ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Stratocumulus Clouds ◽  
Data Source ◽  
Bulk Model ◽  
Microphysical Parameterization ◽  
Les Model

Abstract A microphysical parameterization for shallow cumulus and boundary layer stratocumulus clouds has been developed. Similar to the Khairoutdinov and Kogan parameterization for stratocumulus clouds, the new parameterization is based on an explicit microphysical large-eddy simulation (LES) model as a data source and benchmark for comparison. The predictions of the bulk model using the new parameterization were tested in simulations of shallow cumulus and boundary layer stratocumulus clouds; in both cases the new parameterization matched the predictions of the explicit microphysics LES quite accurately. These results show the importance of the choice of the dataset in parameterization development and the need for it to be balanced by realistic dynamic conditions. The strong sensitivity to representation of rain evaporation is also demonstrated. Accurate formulation of this process, tuned for the case of cumulus convection, has substantially improved precision of rain production.

scholarly journals Seamless Stratocumulus Simulation across the Turbulent Gray Zone

2014 ◽  
Vol 142 (4) ◽  
pp. 1655-1668 ◽  
Author(s):  
I. A. Boutle ◽  
J. E. J. Eyre ◽  
A. P. Lock
Keyword(s):  
Boundary Layer ◽  
Prediction Models ◽  
Weather Prediction ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aircraft Observations ◽  
Microphysical Parameterization ◽  
Grid Length ◽  
Numerical Weather Prediction Models

Abstract A pragmatic approach for representing partially resolved turbulence in numerical weather prediction models is introduced and tested. The method blends a conventional boundary layer parameterization, suitable for large grid lengths, with a subgrid turbulence scheme suitable for large-eddy simulation. The key parameter for blending the schemes is the ratio of grid length to boundary layer depth. The new parameterization is combined with a scale-aware microphysical parameterization and tested on a case study forecast of stratocumulus evolution. Simulations at a range of model grid lengths between 1 km and 100 m are compared to aircraft observations. The improved microphysical representation removes the correlation between precipitation rate and model grid length, while the new turbulence parameterization improves the transition from unresolved to resolved turbulence as grid length is reduced.

scholarly journals Large-Eddy Simulation of Post-Cold-Frontal Continental Stratocumulus

2010 ◽  
Vol 67 (12) ◽  
pp. 3835-3853 ◽  
Author(s):  
David B. Mechem ◽  
Yefim L. Kogan ◽  
David M. Schultz
Keyword(s):  
Boundary Layer ◽  
Climate Models ◽  
Weather Prediction ◽  
Vertical Motion ◽  
Surface Fluxes ◽  
Synoptic Scale ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Stratocumulus Clouds

Abstract Previous large-eddy simulations (LES) of stratocumulus-topped boundary layers have been exclusively set in marine environments. Boundary layer stratocumulus clouds are also prevalent over the continent but have not been simulated previously. A suite of LES runs was performed for a case of continental post-cold-frontal stratocumulus observed by the Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF), located in northern Oklahoma. Comparison with fixed, ground-based sensors necessitated an Eulerian approach in which it was necessary to supply to the model estimates of synoptic-scale advection and vertical motion, particularly given the quickly evolving, baroclinic nature of the synoptic environment. Initial analyses from the Rapid Update Cycle model supplied estimates for these forcing terms. Turbulent statistics calculated from the LES results are consistent with large-eddy observations obtained from millimeter-wave cloud radar. The magnitude of turbulence is weaker than in typical marine stratocumulus, a result attributed to highly decoupled cloud and subcloud circulations associated with a deep layer of negative buoyancy flux arising from the entrainment of warm, free-tropospheric air. Model results are highly sensitive to variations in advection of temperature and moisture and much less sensitive to changes in synoptic-scale vertical velocity and surface fluxes. For this case, moisture and temperature advection, rather than entrainment, tend to be the governing factors in the analyzed cloud system maintenance and decay. Typical boundary layer entrainment scalings applied to this case do not perform very well, a result attributed to the highly decoupled nature of the circulation. Shear production is an important part of the turbulent kinetic energy budget. The dominance of advection provides an optimistic outlook for mesoscale, numerical weather prediction, and climate models because these classes of models represent these grid-scale processes better than they do subgrid-scale processes such as entrainment.

Influência da pluma aquecida de uma chaminé no escoamento turbulento: uma abordagem inicial via simulação

2018 ◽  
Vol 40 ◽  
pp. 45
Author(s):  
Franciano Scremin Puhales ◽  
Otávio Costa Acevedo ◽  
Luis Gustavo Nogueira Martins ◽  
Gervásio Annes Degrazia ◽  
Pablo Eli Soares de Oliveira ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Power Plant ◽  
Turbulent Flows ◽  
Atmospheric Turbulence ◽  
Field Experiments ◽  
Thermal Power ◽  
Atmospheric Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Large Eddy Simulation (LES) have been employed to investigate turbulent flows. In atmospheric turbulence, this methodology is widely used and, sometimes is complementary to field experiments, leading a more detailed about turbulent flow. In this work a LES model was utilized to describe the influence exerted by a hot plume, emitted for a thermal power-plant in the atmospheric flow in the planetary boundary-layer.

scholarly journals LES of a Spatially Developing Atmospheric Boundary Layer: Application of a Fringe Method for the Stratocumulus to Shallow Cumulus Cloud Transition

2014 ◽  
Vol 142 (9) ◽  
pp. 3418-3424 ◽  
Author(s):  
M. Inoue ◽  
G. Matheou ◽  
J. Teixeira
Keyword(s):  
Boundary Layer ◽  
Boundary Conditions ◽  
Atmospheric Boundary Layer ◽  
Cumulus Cloud ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Outflow Boundary Conditions ◽  
Large Eddy ◽  
Inflow Condition ◽  
Outflow Boundary

An arrangement of a large-eddy simulation (LES) is described that facilitates a spatially developing thermally stratified atmospheric boundary layer (ABL). When the inflow and outflow boundary conditions are specified, the LES of stably stratified ABL turns out to be challenging because spurious reflections of waves at the boundary accumulate inside the domain. To tackle this problem, a fringe method with an auxiliary LES running concurrently is applied to enforce upstream/downstream boundary conditions. An artificial forcing term is applied within a fringe region located at the beginning of the main LES domain in order to ensure statistically stationary inflow boundary conditions. The auxiliary LES, which is horizontally homogeneous in a doubly periodic domain, is used to determine the inflow condition of the main LES domain. The present scheme is used to provide an Eulerian perspective of the stratocumulus to shallow cumulus cloud (Sc–Cu) transition, one of the key cloud regimes over the subtropical ocean. In this study, the transition is triggered by increasing the sea surface temperature (SST) and the LES runs until a statistically steady evolution of the Sc–Cu transition is achieved. The flow statistics are compared with those from a recycling-type method and it is found that the fringe method is more suitable for the current applications.

Modeling a Stratocumulus-Topped PBL: Intercomparison among Different One-Dimensional Codes and with Large Eddy Simulation

1996 ◽  
Vol 77 (9) ◽  
pp. 2033-2042 ◽  
Author(s):  
P. Bechtold ◽  
S. K. Krueger ◽  
W. S. Lewellen ◽  
E. van Meijgaard ◽  
C.-H. Moeng ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Water Cycle ◽  
Global Scale ◽  
Model Complexity ◽  
One Dimensional ◽  
Eddy Simulation ◽  
Cloud Water Content ◽  
Large Eddy ◽  
Stratocumulus Clouds

Several one-dimensional (ID) cloud/turbulence ensemble modeling results of an idealized nighttime marine stratocumulus case are compared to large eddy simulation (LES). This type of model intercomparison was one of the objects of the first Global Energy and Water Cycle Experiment Cloud System Study boundary layer modeling workshop held at the National Center for Atmospheric Research on 16–18 August 1994. Presented are results obtained with different 1D models, ranging from bulk models (including only one or two vertical layers) to various types (first order to third order) of multilayer turbulence closure models. The ID results fall within the scatter of the LES results. It is shown that ID models can reasonably represent the main features (cloud water content, cloud fraction, and some turbulence statistics) of a well-mixed stratocumulus-topped boundary layer. Also addressed is the question of what model complexity is necessary and can be afforded for a reasonable representation of stratocumulus clouds in mesoscale or global-scale operational models. Bulk models seem to be more appropriate for climate studies, whereas a multilayer turbulence scheme is best suited in mesoscale models having at least 100- to 200-m vertical resolution inside the boundary layer.

Radiative Impacts on the Growth of Drops within Simulated Marine Stratocumulus. Part II: Solar Zenith Angle Variations

2005 ◽  
Vol 62 (7) ◽  
pp. 2339-2351 ◽  
Author(s):  
Christopher M. Hartman ◽  
Jerry Y. Harrington
Keyword(s):  
Solar Heating ◽  
Size Spectrum ◽  
Residence Times ◽  
Marine Stratocumulus ◽  
Vapor Growth ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Stratocumulus Clouds ◽  
Cooling Effects ◽  
Les Model

Abstract The effects of solar heating at a variety of solar zenith angles (Θo) on the vapor depositional growth of cloud drops, and hence the potential for collection enhancement, is investigated. A large eddy simulation (LES) model is used to predict the evolution of marine stratocumulus clouds subject to changes in Θo. During the course of each simulation, LES output is stored for 600 parcel trajectories and is used to drive an offline microphysical model that includes the influence of radiation on drop growth. Smaller Θo, such as when the sun is overhead, provide strong solar heating, which tends to confine circulations to the cloud layer and leads to long in-cloud residence times for cloud drops. At larger Θo, when solar heating is weak, circulations are stronger and penetrate through the depth of the boundary layer, which causes much shorter in-cloud residence times for cloud drops. Simulations show that this leads to a more rapid collection process in strongly, as compared to weakly solar-heated clouds provided that the liquid water contents of each cloud are similar. When drop vapor growth includes radiative effects, three main results emerge: 1) Solar heating at smaller Θo (0° to 45°) dominates over longwave cooling effects causing a suppression of collection for lower drop concentrations (100 to 200 cm−3). 2) At larger drop concentrations (≳300 cm−3) longwave cooling dominates over solar heating and collection is enhanced. 3) At large Θo (60° to 90°), solar heating is ineffective at modifying the drop size spectrum thus allowing longwave cooling to significantly enhance collection at all drop concentrations above approximately 100 cm−3.

scholarly journals A Dual Mass Flux Framework for Boundary Layer Convection. Part I: Transport

2009 ◽  
Vol 66 (6) ◽  
pp. 1465-1487 ◽  
Author(s):  
Roel A. J. Neggers ◽  
Martin Köhler ◽  
Anton C. M. Beljaars
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Mass Flux ◽  
Model Complexity ◽  
Cumulus Convection ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Simulation Results

Abstract This study considers the question of what is the least complex bulk mass flux framework that can still conceptually reproduce the smoothly varying coupling between the shallow convective cloud layer and the subcloud mixed layer. To this end, the model complexity of the classic single bulk mass flux scheme is enhanced. Inspired by recent large-eddy simulation results, the authors argue that two relatively minor but key conceptual modifications are already sufficient to achieve this goal: (i) retaining a dry transporting updraft in the moist limit and (ii) applying continuous updraft area partitioning to this dual mass flux (DualM) framework. The dry updraft represents all internal mixed layer updrafts that terminate near the mixed layer top, whereas the moist updraft represents all updrafts that condense and rise out of the mixed layer as buoyant cumulus clouds. The continuous area partitioning between the dry and moist updraft is a function of moist convective inhibition above the mixed layer top. Updraft initialization is a function of the updraft area fraction and is therefore consistent with the updraft definition. It is argued that the model complexity thus enhanced is sufficient to allow reproduction of various phenomena involved in the cloud–subcloud coupling, namely (i) dry countergradient transport within the mixed layer that is independent of the moist updraft, (ii) soft triggering of moist convective flux throughout the boundary layer, and (iii) a smooth response to smoothly varying forcings, including the reproduction of gradual transitions to and from shallow cumulus convection. The DualM framework is evaluated by implementing in the Eddy Diffusivity Mass Flux (EDMF) boundary layer scheme of the ECMWF’s Integrated Forecasting System. Single column model experiments are evaluated against large-eddy simulation results for a range of different cases that span a broad parameter space of cloud–subcloud coupling intensities. The results illustrate that also in numerical practice the DualM framework can reproduce gradual transitions to and from shallow cumulus convection. Model behavior is further explored through experiments in which model complexity is purposely reduced, thus mimicking a single bulk updraft setup. This gives more insight into the new model-internal interactions and explains the obtained case results.

scholarly journals Using the Sensitivity of Large-Eddy Simulations to Evaluate Atmospheric Boundary Layer Models

2012 ◽  
Vol 69 (5) ◽  
pp. 1582-1601 ◽  
Author(s):  
Gilles Bellon ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Stationary State ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Tropospheric Temperature ◽  
Unstable Regime ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Bulk Model

Abstract A simple framework to study the sensitivity of atmospheric boundary layer (ABL) models to the large-scale conditions and forcings is introduced. This framework minimizes the number of parameters necessary to describe the large-scale conditions, subsidence, and radiation. Using this framework, the sensitivity of the stationary ABL to the large-scale boundary conditions [underlying sea surface temperature (SST) and overlying humidity and temperature in the free troposphere] is investigated in large-eddy simulations (LESs). For increasing SST or decreasing free-tropospheric temperature, the LES exhibits a transition from a cloud-free, well-mixed ABL stationary state, through a cloudy, well-mixed stationary state and a stable shallow cumulus stationary state, to an unstable regime with a deepening shallow cumulus layer. For a warm SST, when increasing free-tropospheric humidity, the LES exhibits a transition from a stable shallow cumulus stationary state, through a stable cumulus-under-stratus stationary state, to an unstable regime with a deepening, cumulus-under-stratus layer. For a cool SST, when increasing the free-tropospheric humidity, the LES stationary state exhibits a transition from a cloud-free, well-mixed ABL regime, through a well-mixed cumulus-capped regime, to a stratus-capped regime with a decoupling between the subcloud and cloud layers. This dataset can be used to evaluate other ABL models. As an example, the sensitivity of a bulk model based on the mixing-line model is presented. This bulk model reproduces the LES sensitivity to SST and free-tropospheric temperature for the stable and unstable shallow cumulus regimes, but it is less successful at reproducing the LES sensitivity to free-tropospheric humidity for both shallow cumulus and well-mixed regimes.

Large-Eddy Simulation of the Onset of the Sea Breeze

2007 ◽  
Vol 64 (12) ◽  
pp. 4445-4457 ◽  
Author(s):  
M. Antonelli ◽  
R. Rotunno
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Sea Breeze ◽  
Small Scale ◽  
Computational Domain ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Abstract This paper describes results from a large-eddy simulation (LES) model used in an idealized setting to simulate the onset of the sea breeze. As the LES is capable of simulating boundary layer–scale, three-dimensional turbulence along with the mesoscale sea-breeze circulation, a parameterization of the planetary boundary layer was unnecessary. The basic experimental design considers a rotating, uniformly stratified, resting atmosphere that is suddenly heated at the surface over the “land” half of the domain. To focus on the simplest nontrivial problem, the diurnal cycle, effects of moisture, interactions with large-scale winds, and coastline curvature were all neglected in this study. The assumption of a straight coastline allows the use of a rectangular computational domain that extends to 50 km on either side of the coast, but only 5 km along the coast, with 100-m grid intervals so that the small-scale turbulent convective eddies together with the mesoscale sea breeze may be accurately computed. Through dimensional analysis of the simulation results, the length and velocity scales characterizing the simulated sea breeze as functions of the externally specified parameters are identified.

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