scholarly journals Evaluation of Shallow‐Cumulus Entrainment Rate Retrievals Using Large‐Eddy Simulation

2019 ◽  
Vol 124 (16) ◽  
pp. 9624-9643 ◽  
Author(s):  
S. Drueke ◽  
D. J. Kirshbaum ◽  
P. Kollias
Keyword(s):  
Large Eddy Simulation ◽  
Entrainment Rate ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Large Eddy

scholarly journals Explicit aerosol–cloud interactions in the Dutch Atmospheric Large-Eddy Simulation model DALES4.1-M7

2019 ◽  
Vol 12 (12) ◽  
pp. 5177-5196 ◽  
Author(s):  
Marco de Bruine ◽  
Maarten Krol ◽  
Jordi Vilà-Guerau de Arellano ◽  
Thomas Röckmann
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Model ◽  
Large Eddy Simulation Model ◽  
Aerosol Cloud ◽  
Eddy Simulation ◽  
Aerosol Mass ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Microphysical Processes ◽  
Aerosol Cloud Interactions

Abstract. Large-eddy simulation (LES) models are an excellent tool to improve our understanding of aerosol–cloud interactions (ACI). We introduce a prognostic aerosol scheme with multiple aerosol species in the Dutch Atmospheric Large-Eddy Simulation model (DALES), especially focused on simulating the impact of cloud microphysical processes on the aerosol population. The numerical treatment of aerosol activation is a crucial element for simulating both cloud and aerosol characteristics. Two methods are implemented and discussed: an explicit activation scheme based on κ-Köhler theory and a more classic approach using updraught strength. Sample model simulations are based on the Rain in Shallow Cumulus over the Ocean (RICO) campaign, characterized by rapidly precipitating warm-phase shallow cumulus clouds. We find that in this pristine ocean environment virtually all aerosol mass in cloud droplets is the result of the activation process, while in-cloud scavenging is relatively inefficient. Despite the rapid formation of precipitation, most of the in-cloud aerosol mass is returned to the atmosphere by cloud evaporation. The strength of aerosol processing through subsequent cloud cycles is found to be particularly sensitive to the activation scheme and resulting cloud characteristics. However, the precipitation processes are considerably less sensitive. Scavenging by precipitation is the dominant source for in-rain aerosol mass. About half of the in-rain aerosol reaches the surface, while the rest is released by evaporation of falling precipitation. The effect of cloud microphysics on the average aerosol size depends on the balance between the evaporation of clouds and rain and ultimate removal by precipitation. Analysis of typical aerosol size associated with the different microphysical processes shows that aerosols resuspended by cloud evaporation have a radius that is only 5 % to 10 % larger than the originally activated aerosols. In contrast, aerosols released by evaporating precipitation are an order of magnitude larger.

scholarly journals Surface Solar Irradiance in Continental Shallow Cumulus Fields: Observations and Large-Eddy Simulation

2019 ◽  
Vol 77 (3) ◽  
pp. 1065-1080 ◽  
Author(s):  
Jake J. Gristey ◽  
Graham Feingold ◽  
Ian B. Glenn ◽  
K. Sebastian Schmidt ◽  
Hong Chen
Keyword(s):  
Radiative Transfer ◽  
Large Eddy Simulation ◽  
Great Plains ◽  
Solar Irradiance ◽  
Climate Models ◽  
Valuable Insight ◽  
Energy Potential ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Large Eddy

Abstract This study examines shallow cumulus cloud fields and their surface shortwave radiative effects using large-eddy simulation (LES) along with observations across multiple days at the Atmospheric Radiation Measurement Southern Great Plains atmospheric observatory. Pronounced differences are found between probability density functions (PDFs) of downwelling surface solar irradiance derived from observations and LES one-dimensional (1D) online radiation calculations. The shape of the observed PDF is bimodal, which is only reproduced by offline three-dimensional (3D) radiative transfer calculations, demonstrating PDF bimodality as a 3D radiative signature of continental shallow cumuli. Local differences between 3D and 1D radiative transfer calculations of downwelling surface solar irradiance are, on average, larger than 150 W m−2 on one afternoon. The differences are substantially reduced when spatially averaged over the LES domain and temporally averaged over the diurnal cycle, but systematic 3D biases ranging from 2 to 8 W m−2 persist across different days. Covariations between the domain-averaged surface irradiance, framed as a surface cloud radiative effect, and the simulated cloud fraction are found to follow a consistent diurnal relationship, often exhibiting hysteresis. In contrast, observations show highly variable behavior. By subsampling the LES domain, it is shown that this is due to the limited sampling density of inherently 3D observations. These findings help to define observational requirements for detecting such relationships, provide valuable insight for evaluating weather and climate models against surface observations as they push to ever higher resolutions, and have important implications for future assessments of solar renewable energy potential.

Large Eddy Simulation of a Free Circular Jet

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Trushar B. Gohil ◽  
Arun K. Saha ◽  
K. Muralidhar
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Experimental Results ◽  
Entrainment Rate ◽  
Smagorinsky Model ◽  
Potential Core ◽  
Eddy Simulation ◽  
Large Eddy

A large eddy simulation (LES) of an incompressible spatially developing circular jet at a Reynolds number of 10,000 is performed. The shear-improved Smagorinsky model (Lévêque et al., 2007, “A Shear-Improved Smagorinsky Model for the Large-Eddy Simulation of Wall-Bounded Turbulent Flows,” J. Fluid Mech., 570, pp. 491–502) is used for the resolution of the subgrid stress tensor within the filtered three-dimensional unsteady Navier–Stokes equations. Higher-order spatial and temporal discretization schemes are used for capturing the details of the turbulent flow field. With the help of instantaneous and time-averaged flow data, the spatial transition from the laminar state to the turbulent is analyzed. Flow structures are visualized using isosurfaces of the Q-criterion. Instantaneous flow patterns show single tearing and multiple pairing processes. Tracing individual vortex rings over a longer time period, a detailed understanding of the vortex interaction is revealed. The observed trends and the length of the potential core are in conformity with the findings of earlier experiments. The time-averaged axial velocity profile shows that the jet attains self-similarity and the computed profile matches well with the experimental results of Hussein et al. (1994, “Velocity Measurements in a High-Reynolds-Number, Momentum-Conserving, Axisymmetric, Turbulent Jet,” J. Fluid Mech., 258, pp. 31–75). The centerline decay of the velocity and entrainment rate are in agreement with published experiments. The Reynolds stress components u'u'¯, v'v'¯, and u'v'¯ and the third-order velocity moment are in good agreement with thr experimental results, thus confirming the validity of the present simulation.

scholarly journals Explicit aerosol-cloud interaction in the Dutch Atmospheric Large-Eddy Simulation model DALES4.1-M7

2019 ◽  
Author(s):  
Marco de Bruine ◽  
Maarten Krol ◽  
Jordi Vilà-Guerau de Arellano ◽  
Thomas Röckmann
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Model ◽  
Large Eddy Simulation Model ◽  
Aerosol Cloud ◽  
Eddy Simulation ◽  
Aerosol Mass ◽  
Shallow Cumulus ◽  
Cloud Characteristics ◽  
Large Eddy ◽  
Order Of Magnitude

Abstract. Large-Eddy Simulations (LES) are an excellent tool to improve our understanding of the aerosol-cloud interaction (ACI). These models combine a spatial resolution high enough to resolve cloud structures with domain sizes large enough to simulate macroscale dynamics and feedback between clouds. However, most research on ACI using LES simulations is focused on changes in cloud characteristics. The feedback of ACI on the aerosol population remains relatively understudied. We introduce a prognostic aerosol scheme with multiple aerosol species in the Dutch Atmospheric Large-Eddy Simulation model (DALES), especially focused on simulating the feedback of ACI on the aerosol population. The numerical treatment of aerosol activation is a crucial element in the simulation of ACI. Two methods are implemented and discussed: an explicit activation scheme based on κ-Köhler theory and a more classic approach using updraft strength. Model simulations are validated against observations using the Rain in Shallow Cumulus over the Ocean (RICO) campaign, characterised by rapidly precipitating, warm-phase shallow cumulus clouds. We find that in this pristine ocean environment virtually all aerosols enter the cloud phase through activation while in-cloud scavenging is relatively inefficient. Despite the rapid formation of precipitation, most of the in-cloud aerosol mass is returned to the atmosphere by cloud evaporation. The strength of aerosol processing through subsequent cloud cycles is found to be particularly sensitive to the activation scheme and resulting cloud characteristics. However, the precipitation processes are considerably less sensitive. Scavenging by precipitation is the dominant source for in-rain aerosol mass. About half of the in-rain aerosol reaches the surface, while the rest is released by evaporation of falling precipitation. Whether ACI increases or decreases the average aerosol size depends on the balance between the evaporation of clouds and rain, and ultimate removal by precipitation. Analysis of typical aerosol size associated with the different microphysical processes shows that aerosols resuspended by cloud evaporation are only 5 to 10 % larger than the originally activated aerosols. In contrast, aerosols released by evaporating precipitation are an order of magnitude larger.

scholarly journals Sensitivity to Physical and Numerical Aspects of Large-Eddy Simulation of Stratocumulus

2019 ◽  
Vol 147 (7) ◽  
pp. 2621-2639 ◽  
Author(s):  
Georgios Matheou ◽  
João Teixeira
Keyword(s):  
Numerical Model ◽  
Large Eddy Simulation ◽  
Radiative Cooling ◽  
Model Parameters ◽  
Turbulence Structure ◽  
Entrainment Rate ◽  
Fine Grid ◽  
Eddy Simulation ◽  
Grid Convergence ◽  
Large Eddy

Abstract A series of numerical experiments where both physical and numerical model parameters are varied with respect to a reference setup is used to investigate the physics of a stratocumulus cloud and the performance of a large-eddy simulation (LES) model. The simulations show a delicate balance of physical processes with some sensitivities amplified by numerical model features. A strong feedback between cloud liquid, cloud-top radiative cooling, and turbulence leads to slow grid convergence of the turbulent fluxes. For a methodology that diagnoses cloud liquid from conserved variables, small errors in the total water amount result in large liquid water errors, which are amplified by the cloud-top radiative cooling leading to large variations of buoyancy forcing. In contrast, when the liquid–radiation–buoyancy feedback is not present in simulations without radiation, the turbulence structure of the boundary layer remains essentially identical for grid resolutions between 20 and 1.25 m. The present runs suggest that the buoyancy reversal instability significantly enhances the entrainment rate. Even though cloud-top radiative cooling is regarded as a key attribute of stratocumulus, the present simulations suggest that surface fluxes and surface shear significantly contribute to the total turbulent kinetic energy. Turbulence spectra exhibit inertial range scaling away from the confinement effects of the surface and inversion. Fine grid resolution LESs agree with observations, especially with respect to cloud liquid and vertical velocity variance, and exhibit grid convergence without any model tuning or ad hoc model choices.

scholarly journals A Large Eddy Simulation Intercomparison Study of Shallow Cumulus Convection

2003 ◽  
Vol 60 (10) ◽  
pp. 1201-1219 ◽  
Author(s):  
A. Pier Siebesma ◽  
Christopher S. Bretherton ◽  
Andrew Brown ◽  
Andreas Chlond ◽  
Joan Cuxart ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Cumulus Convection ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Intercomparison Study
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