scholarly journals iGen 0.1: the automated generation of a parameterisation of entrainment in marine stratocumulus

2011 ◽  
Vol 4 (3) ◽  
pp. 797-807 ◽  
Author(s):  
D. F. Tang ◽  
S. Dobbie
Keyword(s):  
Large Scale ◽  
Source Code ◽  
Marine Stratocumulus ◽  
Automated Generation ◽  
Entrainment Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Resolution Model ◽  
High Resolution Model ◽  
A New Technique

Abstract. In a previous paper we described a new technique for automatically generating parameterisations using a program called iGen. iGen generates parameterisations by analysing the source code of a~high resolution model that resolves the physics to be parameterised. In order to demonstrate that this technique scales up to deal with models of realistic complexity we have used iGen to generate a parameterisation of entrainment in marine stratocumulus. We describe how iGen was used to analyse the source code of an eddy resolving model (ERM) and generate a parameterisation of entrainment velocity in marine stratocumulus in terms of the large-scale state of the boundary layer. The parameterisation was tested against results from the DYCOMS-II intercomparison of ERM models and iGen's parameterisation of mean entrainment velocity was found to be 5.27 × 10−3 ± 0.62 × 10−3 m s−1 compared to 5.2 × 10−3 ± 0.8 × 10−3 m s−1 for the DYCOMS-II ensemble of large eddy simulation (LES) models.

scholarly journals iGen: the automated generation of a parameterisation of entrainment in marine stratocumulus

2011 ◽  
Vol 4 (2) ◽  
pp. 971-995 ◽  
Author(s):  
D. F. Tang ◽  
S. Dobbie
Keyword(s):  
Large Scale ◽  
Source Code ◽  
Marine Stratocumulus ◽  
Automated Generation ◽  
Entrainment Velocity ◽  
Cloud Resolving Model ◽  
Resolution Model ◽  
High Resolution Model ◽  
The Mean ◽  
A New Technique

Abstract. In a previous paper we described a new technique for automatically generating parameterisations using a program called iGen. iGen generates parameterisations by analysing the source code of a high resolution model that resolves the physics to be parameterised. In order to demonstrate that this technique scales up to deal with models of realistic complexity we have used iGen to generate a parameterisation of entrainment in marine stratocumulus. We present details of our technique in which iGen was used to analyse the source code of a cloud resolving model and generate a parameterisation of the mean and standard deviation of entrainment velocity in marine stratocumulus in terms of the large-scale state of the boundary layer. The parameterisation was tested against results from the DYCOMS-II intercomparison of cloud resolving models and iGen's parameterisation of mean entrainment velocity was found to be 5.27 × 10−3 ± 0.62 × 10−3 m s−1 compared to 5.2 × 10−3 ± 0.8 × 10−3 m s−1 for the DYCOMS-II ensemble of cloud resolving models.

scholarly journals The effect of black carbon on aerosol-boundary layer feedback: Potential implications for Beijing haze episodes

2021 ◽  
Author(s):  
Jessica Slater ◽  
Hugh Coe ◽  
Gordon McFiggans ◽  
Juha Tonttila ◽  
Sami Romakkaniemi
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Black Carbon ◽  
Lower Atmosphere ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Resolution Model ◽  
Haze Episode ◽  
High Resolution Model ◽  
The Impact

Abstract. Beijing suffers from poor air quality particularly during wintertime haze episodes when concentrations of PM2.5 can peak at > 400 ug/m3. Black carbon (BC), an aerosol which strongly absorbs solar radiation can make up to 10 % of PM2.5 in Beijing. Black carbon is of interest due to its climatic and health impacts. Black carbon has also been found to impact planetary boundary layer (PBL) meteorology. Through interacting with radiation and altering the thermal profile of the lower atmosphere, BC can either suppress or enhance PBL development to various degrees depending on the properties and altitude of the BC layer.Previous research assessing the impact of BC on PBL meteorology has been investigated through the use of regional models which are limited both by resolution and the chosen boundary layer schemes. In this work, we apply a high resolution coupled large eddy simulation-aerosol-radiation model (UCLALES-SALSA) to quantify the impact of black carbon at different altitudes on PBL dynamics using conditions from a specific haze episode which occurred from 1st–4th Dec 2016 in Beijing. Results presented in this paper quantify the heating rate of BC at various altitudes to be between 0.01 and 0.016 K/h per μg/m3 of BC, increasing with altitude but decreasing across the PBL. Through utilising a high resolution model which explicitly calculates turbulent dynamics, this paper showcases the impact of BC on PBL dynamics both within and above the PBL. These results show that BC within the PBL increases maximum PBL height by 0.4 % but that the same loading of BC above the PBL can suppress PBL height by 6.5 %. Furthermore, when BC is present throughout the column the impact of BC suppressing PBL development is further maximised, with BC causing a 17 % decrease in maximum PBL height compared to only scattering aerosols. Combining these results in this paper, we present a mechanism through which BC may play a prominent role in the intensity and longevity of Beijing’s pollution episodes.

The vertical structure of mid-latitude marine stratocumulus simulated by large eddy simulation

2020 ◽  
Author(s):  
Yangze Ren ◽  
Huiwen Xue
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Cellular Structure ◽  
Large Scale ◽  
Vertical Structure ◽  
Temperature Inversion ◽  
Liquid Water Content ◽  
Marine Stratocumulus ◽  
Eddy Simulation ◽  
Large Eddy

<p>Cloud feedback in mid-latitude marine stratocumulus is not clearly understood due to few reliable observations. Stratocumulus cloud is the most frequent and extensive cloud type over mid-latitude marine areas and has strong short-wave radiative effect. In this study, large eddy simulation (LES) is used to resolve the vertical structure of mid-latitude marine stratocumulus. We find that, in the wintertime over North Pacific, stratocumulus cloud often forms in regions of high pressure and large-scale sinking motion, and can remain in steady-state for a couple of days. We then choose two typical cases to do LES simulation: One has a lower cloud top height and a stronger temperature inversion (case l), without mesoscale cellular structure; the other has a higher cloud top height and a weaker temperature inversion (case h), with closed-cell cellular structure. The liquid water content profiles are adiabatic, and the boundary layer is well-mixed for both cases. In case l, the main source of turbulent kinetic energy (TKE) is from cloud top long-wave radiative cooling for the entire boundary layer. In case h, TKE production due to cloud-top longwave cooling is only significant in the cloud layer, and the subcloud layer TKE is mainly from surface processes.</p>

scholarly journals iGen: a program for the automated generation of models and parameterisations

2011 ◽  
Vol 4 (2) ◽  
pp. 843-868 ◽  
Author(s):  
D. F. Tang ◽  
S. Dobbie
Keyword(s):  
High Resolution ◽  
Source Code ◽  
Model Development ◽  
New Approach ◽  
Physical Systems ◽  
Automated Generation ◽  
Resolution Model ◽  
High Resolution Model ◽  
High Resolution Models ◽  
Very High

Abstract. Complex physical systems can often be simulated using very high-resolution models but this is not always practical because of computational restrictions. In this case the model must be simplified or parameterised, but this is a notoriously difficult process that often requires the introduction of "model assumptions" that are hard or impossible to justify. Here we introduce a new approach to parameterising models. The approach makes use of a newly developed computer program, which we call iGen, that analyses the source code of a high-resolution model and formally derives a much faster parameterised model that closely approximates the original, reporting bounds on the error introduced by any approximations. These error bounds can be used to formally justify use of the parameterised model in subsequent numerical experiments. Using increasingly complex physical systems as examples we illustrate that iGen has the ability to produce parameterisations that run typically orders of magnitude faster than the underlying, high-resolution models from which they are derived and show that iGen has the potential to become an important tool in model development.

scholarly journals Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

2017 ◽  
Vol 17 (11) ◽  
pp. 7261-7276 ◽  
Author(s):  
Tobias Wolf-Grosse ◽  
Igor Esau ◽  
Joachim Reuder
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
Large Eddy Simulation ◽  
Air Pollutants ◽  
Large Scale ◽  
Wind Speeds ◽  
Street Level ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Air Pockets

Abstract. Street-level urban air pollution is a challenging concern for modern urban societies. Pollution dispersion models assume that the concentrations decrease monotonically with raising wind speed. This convenient assumption breaks down when applied to flows with local recirculations such as those found in topographically complex coastal areas. This study looks at a practically important and sufficiently common case of air pollution in a coastal valley city. Here, the observed concentrations are determined by the interaction between large-scale topographically forced and local-scale breeze-like recirculations. Analysis of a long observational dataset in Bergen, Norway, revealed that the most extreme cases of recurring wintertime air pollution episodes were accompanied by increased large-scale wind speeds above the valley. Contrary to the theoretical assumption and intuitive expectations, the maximum NO2 concentrations were not found for the lowest 10 m ERA-Interim wind speeds but in situations with wind speeds of 3 m s−1. To explain this phenomenon, we investigated empirical relationships between the large-scale forcing and the local wind and air quality parameters. We conducted 16 large-eddy simulation (LES) experiments with the Parallelised Large-Eddy Simulation Model (PALM) for atmospheric and oceanic flows. The LES accounted for the realistic relief and coastal configuration as well as for the large-scale forcing and local surface condition heterogeneity in Bergen. They revealed that emerging local breeze-like circulations strongly enhance the urban ventilation and dispersion of the air pollutants in situations with weak large-scale winds. Slightly stronger large-scale winds, however, can counteract these local recirculations, leading to enhanced surface air stagnation. Furthermore, this study looks at the concrete impact of the relative configuration of warmer water bodies in the city and the major transport corridor. We found that a relatively small local water body acted as a barrier for the horizontal transport of air pollutants from the largest street in the valley and along the valley bottom, transporting them vertically instead and hence diluting them. We found that the stable stratification accumulates the street-level pollution from the transport corridor in shallow air pockets near the surface. The polluted air pockets are transported by the local recirculations to other less polluted areas with only slow dilution. This combination of relatively long distance and complex transport paths together with weak dispersion is not sufficiently resolved in classical air pollution models. The findings have important implications for the air quality predictions over urban areas. Any prediction not resolving these, or similar local dynamic features, might not be able to correctly simulate the dispersion of pollutants in cities.

Comparative Large Eddy Simulation study of a large-scale buoyant fire

2011 ◽  
Vol 47 (9) ◽  
pp. 1197-1208 ◽  
Author(s):  
G. H. Yeoh ◽  
S. C. P. Cheung ◽  
J. Y. Tu ◽  
T. J. Barber
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Study ◽  
Large Scale ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals High Resolution Model Intercomparison Project (HighResMIP)

2016 ◽  
Author(s):  
R. J. Haarsma ◽  
M. Roberts ◽  
P. L. Vidale ◽  
C. A. Senior ◽  
A. Bellucci ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Computational Cost ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Model Intercomparison ◽  
Resolution Model ◽  
Intercomparison Project ◽  
High Resolution Model ◽  
The Impact

Abstract. Robust projections and predictions of climate variability and change, particularly at regional scales, rely on the driving processes being represented with fidelity in model simulations. The role of enhanced horizontal resolution in improved process representation in all components of the climate system is of growing interest, particularly as some recent simulations suggest the possibility for significant changes in both large-scale aspects of circulation, as well as improvements in small-scale processes and extremes. However, such high resolution global simulations at climate time scales, with resolutions of at least 50 km in the atmosphere and 0.25° in the ocean, have been performed at relatively few research centers and generally without overall coordination, primarily due to their computational cost. Assessing the robustness of the response of simulated climate to model resolution requires a large multi-model ensemble using a coordinated set of experiments. The Coupled Model Intercomparison Project 6 (CMIP6) is the ideal framework within which to conduct such a study, due to the strong link to models being developed for the CMIP DECK experiments and other MIPs. Increases in High Performance Computing (HPC) resources, as well as the revised experimental design for CMIP6, now enables a detailed investigation of the impact of increased resolution up to synoptic weather scales on the simulated mean climate and its variability. The High Resolution Model Intercomparison Project (HighResMIP) presented in this paper applies, for the first time, a multi-model approach to the systematic investigation of the impact of horizontal resolution. A coordinated set of experiments has been designed to assess both a standard and an enhanced horizontal resolution simulation in the atmosphere and ocean. The set of HighResMIP experiments is divided into three tiers consisting of atmosphere-only and coupled runs and spanning the period 1950-2050, with the possibility to extend to 2100, together with some additional targeted experiments. This paper describes the experimental set-up of HighResMIP, the analysis plan, the connection with the other CMIP6 endorsed MIPs, as well as the DECK and CMIP6 historical simulation. HighResMIP thereby focuses on one of the CMIP6 broad questions: “what are the origins and consequences of systematic model biases?”, but we also discuss how it addresses the World Climate Research Program (WCRP) grand challenges.

Crackle Noise in Heated Supersonic Jets

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joseph W. Nichols ◽  
Sanjiva K. Lele ◽  
Frank E. Ham ◽  
Steve Martens ◽  
John T. Spyropoulos
Keyword(s):  
Large Scale ◽  
Supersonic Jet ◽  
Supersonic Jets ◽  
Scale Model ◽  
Positive Pressure ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Total Temperature ◽  
Large Scale Flow ◽  
Large Eddies

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, “The Effect of Chevrons on Crackle—Engine and Scale Model Results,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.

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