scholarly journals Lagrangian Investigation of the Precipitation Efficiency of Convective Clouds

2015 ◽  
Vol 72 (3) ◽  
pp. 1045-1062 ◽  
Author(s):  
Wolfgang Langhans ◽  
Kyongmin Yeo ◽  
David M. Romps
Keyword(s):  
Large Eddy Simulations ◽  
Cloud Base ◽  
Water Molecules ◽  
Lagrangian Particle ◽  
Surface Precipitation ◽  
Convective Clouds ◽  
Precipitation Efficiency ◽  
Surface Rainfall ◽  
Large Eddy ◽  
Cumulus Congestus

Abstract The precipitation efficiency of cumulus congestus clouds is investigated with a new Lagrangian particle framework for large-eddy simulations. The framework is designed to track particles representative of individual water molecules. A Monte Carlo approach facilitates the transition of particles between the different water classes (e.g., vapor, rain, or graupel). With this framework, it is possible to reconstruct the pathways of water as it moves from vapor at a particular altitude to rain at the surface. By tracking water molecules through both physical and microphysical space, the precipitation efficiency can be studied in detail as a function of height. Large-eddy simulations of individual cumulus congestus clouds show that the clouds convert entrained vapor to surface precipitation with an efficiency of around 10%. About two-thirds of all vapor that enters the cloud does so by entrainment in the free troposphere, but free-tropospheric vapor accounts for only one-third to one-half of the surface rainfall, with the remaining surface rainfall originating as vapor entrained through the cloud base. The smaller efficiency with which that laterally entrained water is converted into surface precipitation results from the smaller efficiencies with which it condenses, forms precipitating hydrometeors, and reaches the surface.

scholarly journals Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer

2009 ◽  
Vol 137 (3) ◽  
pp. 1083-1110 ◽  
Author(s):  
Andrew S. Ackerman ◽  
Margreet C. vanZanten ◽  
Bjorn Stevens ◽  
Verica Savic-Jovcic ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Water ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Average Maximum ◽  
Large Eddy ◽  
The Mean

Abstract Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.

scholarly journals Measurement of Convective Entrainment Using Lagrangian Particles

2013 ◽  
Vol 70 (1) ◽  
pp. 266-277 ◽  
Author(s):  
Kyongmin Yeo ◽  
David M. Romps
Keyword(s):  
Direct Measurement ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Environmental Air ◽  
Cumulus Congestus ◽  
Entrained Air ◽  
Eulerian Methods ◽  
Good Agreement

Abstract Lagrangian particle tracking is used in a large-eddy simulation to study an individual cumulus congestus. This allows for the direct measurement of the convective entrainment rate and of the residence times of entrained parcels within the cloud. The entrainment rate obtained by Lagrangian direct measurement is found to be higher than that obtained using the recently introduced method of Eulerian direct measurement. This discrepancy is explained by the fast recirculation of air in and out of cloudy updrafts, which Eulerian direct measurement is unable to resolve. By filtering these fast recirculations, the Lagrangian calculation produces a result in very good agreement with the Eulerian calculation. The Lagrangian method can also quantify some aspects of entrainment that cannot be probed with Eulerian methods. For instance, it is found that more than half of the air that is entrained by the cloud during its lifetime is air that was previously detrained by the cloud. Nevertheless, the cloud is highly diluted by entrained air: for cloudy air above 2 km, its mean height of origin is well above the cloud base. This paints a picture of a cloud that rapidly entrains both environmental air and its own detritus.

scholarly journals Large Eddy Simulation of Microphysics and Influencing Factors in Shallow Convective Clouds

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 485
Author(s):  
Zhuangzhuang Zhou ◽  
Chongzhi Yin ◽  
Chunsong Lu ◽  
Xingcan Jia ◽  
Fang Ye ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Influencing Factors ◽  
Vertical Velocity ◽  
Large Scale ◽  
Cloud Droplet ◽  
Relative Dispersion ◽  
Cloud Base ◽  
Convective Clouds ◽  
Eddy Simulation ◽  
Large Eddy

A flight of shallow convective clouds during the SCMS95 (Small Cumulus Microphysics Study 1995) observation project is simulated by the large eddy simulation (LES) version of the Weather Research and Forecasting Model (WRF-LES) with spectral bin microphysics (SBM). This study focuses on relative dispersion of cloud droplet size distributions, since its influencing factors are still unclear. After validation of the simulation by aircraft observations, the factors affecting relative dispersion are analyzed. It is found that the relationships between relative dispersion and vertical velocity, and between relative dispersion and adiabatic fraction are both negative. Furthermore, the negative relationships are relatively weak near the cloud base, strengthen with the increasing height first and then weaken again, which is related to the interplays among activation, condensation and evaporation for different vertical velocity and entrainment conditions. The results will be helpful to improve parameterizations related to relative dispersion (e.g., autoconversion and effective radius) in large-scale models.

scholarly journals Turbulence effects on warm-rain formation in precipitating shallow convection revisited

2016 ◽  
Vol 16 (18) ◽  
pp. 12127-12141 ◽  
Author(s):  
Axel Seifert ◽  
Ryo Onishi
Keyword(s):  
Isotropic Turbulence ◽  
Large Eddy Simulations ◽  
Small Scale ◽  
Shallow Convection ◽  
Surface Precipitation ◽  
Considerable Uncertainty ◽  
Warm Rain ◽  
Large Eddy ◽  
Turbulence Effects ◽  
Rain Formation

Abstract. Two different collection kernels which include turbulence effects on the collision rate of liquid droplets are used as a basis to develop a parameterization of the warm-rain processes autoconversion, accretion, and self-collection. The new parameterization is tested and validated with the help of a 1-D bin microphysics model. Large-eddy simulations of the rain formation in shallow cumulus clouds confirm previous results that turbulence effects can significantly enhance the development of rainwater in clouds and the occurrence and amount of surface precipitation. The detailed behavior differs significantly for the two turbulence models, revealing a considerable uncertainty in our understanding of such effects. In addition, the large-eddy simulations show a pronounced sensitivity to grid resolution, which suggests that besides the effect of sub-grid small-scale isotropic turbulence which is parameterized as part of the collection kernel also the larger turbulent eddies play an important role for the formation of rain in shallow clouds.

scholarly journals Reconciling Differences Between Large‐Eddy Simulations and Doppler Lidar Observations of Continental Shallow Cumulus Cloud‐Base Vertical Velocity

2019 ◽  
Vol 46 (20) ◽  
pp. 11539-11547 ◽  
Author(s):  
Satoshi Endo ◽  
Damao Zhang ◽  
Andrew M. Vogelmann ◽  
Pavlos Kollias ◽  
Katia Lamer ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Doppler Lidar ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Lidar Observations

scholarly journals Mixing in Shallow Cumulus Clouds Studied by Lagrangian Particle Tracking

2008 ◽  
Vol 65 (8) ◽  
pp. 2581-2597 ◽  
Author(s):  
Thijs Heus ◽  
Gertjan van Dijk ◽  
Harm J. J. Jonker ◽  
Harry E. A. Van den Akker
Keyword(s):  
Particle Tracking ◽  
Large Eddy Simulations ◽  
Lagrangian Particle Tracking ◽  
Lagrangian Particle ◽  
Cumulus Clouds ◽  
Lagrangian Particles ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Mixing Diagrams ◽  
Entrained Air

Abstract Mixing between shallow cumulus clouds and their environment is studied using large-eddy simulations. The origin of in-cloud air is studied by two distinct methods: 1) by analyzing conserved variable mixing diagrams (Paluch diagrams) and 2) by tracing back cloud-air parcels represented by massless Lagrangian particles that follow the flow. The obtained Paluch diagrams are found to be similar to many results in the literature, but the source of entrained air found by particle tracking deviates from the source inferred from the Paluch analysis. Whereas the classical Paluch analysis seems to provide some evidence for cloud-top mixing, particle tracking shows that virtually all mixing occurs laterally. Particle trajectories averaged over the entire cloud ensemble also clearly indicate the absence of significant cloud-top mixing in shallow cumulus clouds.

scholarly journals Turbulence effects on warm rain formation in precipitating shallow convection revisited

2016 ◽  
Author(s):  
Axel Seifert ◽  
Ryo Onishi
Keyword(s):  
Isotropic Turbulence ◽  
Large Eddy Simulations ◽  
Small Scale ◽  
Shallow Convection ◽  
Surface Precipitation ◽  
Considerable Uncertainty ◽  
Warm Rain ◽  
Large Eddy ◽  
Turbulence Effects ◽  
Rain Formation

Abstract. Two different collection kernels which include turbulence effects on the collision rate of liquid droplets are used as a basis to develop a parameterization of the warm rain processes autoconversion, accretion and selfcollection. The new parameterization is tested and validated with help of a 1D bin microphysics model. Large-eddy simulations of the rain formation in shallow cumulus clouds confirm previous results that turbulence effects can significantly enhance the development of rain water in clouds and the occurrence and amount of surface precipitation. The detailed behavior differs significantly for the two turbulence models revealing a considerable uncertainty in our understanding of such effects. In addition, the large-eddy simulations show a pronounced sensitivity to grid resolution which suggests that besides the effect of sub-grid small scale isotropic turbulence which is parameterized as part of the collection kernel also the larger turbulent eddies play an important role for the formation of rain in shallow clouds.

Large Eddy Simulations of a Bubbly Mixing Layer

2002 ◽  
Author(s):  
A. Smirnov ◽  
I. Celik ◽  
S. Shi
Keyword(s):  
Mixing Layer ◽  
Particle Dynamics ◽  
Large Eddy Simulations ◽  
Lagrangian Particle ◽  
Two Phase ◽  
Generation Technique ◽  
Flow Generation ◽  
Large Eddy ◽  
Random Flow ◽  
Good Agreement

In this paper we present the results of the application of a Lagrangian particle dynamics (LPD) method and a random flow generation technique (RFG) developed by the authors used in conjunction with large eddy simulations (LES) applied to the case of a two-phase bubbly mixing layer. The objective is to validate the present hybrid Lagrangian-Eulerian approach within the context of LES. The dynamics of the vortices and bubble concentrations reproduced in simulations are in a good agreement with experimental data.

Randomness in the amount of rain in LES with Lagrangian microphysics

2021 ◽  
Author(s):  
Piotr Zmijewski ◽  
Piotr Dziekan ◽  
Hanna Pawlowska
Keyword(s):  
Stochastic Process ◽  
Cloud Model ◽  
Cloud Microphysics ◽  
Large Eddy Simulations ◽  
Lagrangian Particle ◽  
Vast Number ◽  
Popular Method ◽  
Large Eddy ◽  
The University ◽  
Spatial Cell

<p>Lagrangian, particle-based models are an emerging method for detailed modeling of cloud microphysics. In these models, a relatively small number of "super-droplets" is used to represent all hydrometeors. Each super-droplet represents vast number of hydrometeors that have the same properties. The most popular method for solving collision-coalescence in these particle-based models is the all-or-nothing algorithm. In this algorithm, collision-coalescence of droplets within a spatial cell is modeled with a stochastic process. The number of trials is proportional to the number of super-droplets, which is significantly lower than the number of hydrometeors. Therefore the variance of the number of hydrometeors with a given size is higher in the super-droplet algorithm than it would be if every droplet was modeled separately. The increase of this variability depends on the number of super-droplets. We use the University of Warsaw Lagrangian Cloud Model (UWLCM) to analyse how the randomness in the collision-coalescence algorithm affects the amount of precipitation in large eddy simulations of warm clouds.</p>

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