Parameterization of Entrainment Rate and Mass Flux in Continental Cumulus Clouds: Inference From Large Eddy Simulation

2019 ◽  
Vol 124 (23) ◽  
pp. 13127-13139 ◽  
Author(s):  
Sudarsan Bera ◽  
Thara V. Prabha
Keyword(s):  
Large Eddy Simulation ◽  
Mass Flux ◽  
Entrainment Rate ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Improving Parameterization of Entrainment Rate for Shallow Convection with Aircraft Measurements and Large-Eddy Simulation

2016 ◽  
Vol 73 (2) ◽  
pp. 761-773 ◽  
Author(s):  
Chunsong Lu ◽  
Yangang Liu ◽  
Guang J. Zhang ◽  
Xianghua Wu ◽  
Satoshi Endo ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Vertical Velocity ◽  
Dissipation Rate ◽  
Principal Component ◽  
Entrainment Rate ◽  
Shallow Convection ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Multiple Variables

AbstractThis work examines the relationships of entrainment rate to vertical velocity, buoyancy, and turbulent dissipation rate by applying stepwise principal component regression to observational data from shallow cumulus clouds collected during the Routine Atmospheric Radiation Measurement (ARM) Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site near Lamont, Oklahoma. The cumulus clouds during the RACORO campaign simulated using a large-eddy simulation (LES) model are also examined with the same approach. The analysis shows that a combination of multiple variables can better represent entrainment rate in both the observations and LES than any single-variable fitting. Three commonly used parameterizations are also tested on the individual cloud scale. A new parameterization is thus presented that relates entrainment rate to vertical velocity, buoyancy, and dissipation rate; the effects of treating clouds as ensembles and humid shells surrounding cumulus clouds on the new parameterization are discussed. Physical mechanisms underlying the relationships of entrainment rate to vertical velocity, buoyancy, and dissipation rate are also explored.

scholarly journals Large-eddy simulation of organized precipitating trade wind cumulus clouds

2013 ◽  
Vol 13 (1) ◽  
pp. 1855-1889 ◽  
Author(s):  
A. Seifert ◽  
T. Heus
Keyword(s):  
Large Eddy Simulation ◽  
Trade Wind ◽  
Shallow Convection ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Cold Pools ◽  
Cloud Clusters ◽  
Large Eddy ◽  
Sensitivity Studies ◽  
The Individual

Abstract. Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulations experiments the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions can have a pronounced impact on the onset of cloud organization.

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 On the Equivalence of Two Schemes for Convective Momentum Transport

2012 ◽  
Vol 69 (12) ◽  
pp. 3491-3500 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Mass Flux ◽  
Deep Convection ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Convective Momentum Transport

Abstract The Gregory–Kershaw–Inness (GKI) parameterization of convective momentum transport, which has a tunable parameter C, is shown to be identical to a parameterization with no pressure gradient force and a mass flux smaller by a factor of 1 − C. Using cloud-resolving simulations, the transilient matrix for momentum is diagnosed for deep convection in radiative–convective equilibrium. Using this transilient matrix, it is shown that the GKI scheme underestimates the compensating subsidence of momentum by a factor of 1 − C, as predicted. This result is confirmed using a large-eddy simulation.

scholarly journals Large-eddy simulation of organized precipitating trade wind cumulus clouds

2013 ◽  
Vol 13 (11) ◽  
pp. 5631-5645 ◽  
Author(s):  
A. Seifert ◽  
T. Heus
Keyword(s):  
Large Eddy Simulation ◽  
Trade Wind ◽  
Shallow Convection ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Cold Pools ◽  
Cloud Clusters ◽  
Large Eddy ◽  
Sensitivity Studies ◽  
The Individual

Abstract. Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulation experiments, the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions can have a pronounced impact on the onset of cloud organization.

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.

A large-eddy simulation study of cumulus clouds over land and sensitivity to soil moisture

2001 ◽  
Vol 59-60 ◽  
pp. 373-392 ◽  
Author(s):  
Jean-Christophe Golaz ◽  
Hongli Jiang ◽  
William R Cotton
Keyword(s):  
Soil Moisture ◽  
Large Eddy Simulation ◽  
Simulation Study ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Large Eddy
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