scholarly journals Galilean invariance of shallow cumulus convection large-eddy simulations

2021 ◽  
Vol 427 ◽  
pp. 110012
Author(s):  
Oumaima Lamaakel ◽  
Georgios Matheou
Keyword(s):  
Large Eddy Simulations ◽  
Cumulus Convection ◽  
Galilean Invariance ◽  
Shallow Cumulus ◽  
Large Eddy

Responses of Shallow Cumulus Convection to Large-Scale Temperature and Moisture Perturbations: A Comparison of Large-Eddy Simulations and a Convective Parameterization Based on Stochastically Entraining Parcels

2012 ◽  
Vol 69 (6) ◽  
pp. 1936-1956 ◽  
Author(s):  
Ji Nie ◽  
Zhiming Kuang
Keyword(s):  
Large Scale ◽  
Potential Temperature ◽  
Large Eddy Simulations ◽  
Cumulus Parameterization ◽  
Temperature Perturbation ◽  
Cumulus Convection ◽  
Positive Temperature ◽  
Shallow Cumulus ◽  
Scale Temperature ◽  
Large Eddy

Abstract Responses of shallow cumuli to large-scale temperature/moisture perturbations are examined through diagnostics of large-eddy simulations (LESs) of the undisturbed Barbados Oceanographic and Meteorological Experiment (BOMEX) case and a stochastic parcel model. The perturbations are added instantaneously and allowed to evolve freely afterward. The parcel model reproduces most of the changes in the LES-simulated cloudy updraft statistics in response to the perturbations. Analyses of parcel histories show that a positive temperature perturbation forms a buoyancy barrier, which preferentially eliminates parcels that start with lower equivalent potential temperature or have experienced heavy entrainment. Besides the amount of entrainment, the height at which parcels entrain is also important in determining their fate. Parcels entraining at higher altitudes are more likely to overcome the buoyancy barrier than those entraining at lower altitudes. Stochastic entrainment is key for the parcel model to reproduce the LES results. Responses to environmental moisture perturbations are quite small compared to those to temperature perturbations because changing environmental moisture is ineffective in modifying buoyancy in the BOMEX shallow cumulus case. The second part of the paper further explores the feasibility of a stochastic parcel–based cumulus parameterization. Air parcels are released from the surface layer and temperature/moisture fluxes effected by the parcels are used to calculate heating/moistening tendencies due to both cumulus convection and boundary layer turbulence. Initial results show that this conceptually simple parameterization produces realistic convective tendencies and also reproduces the LES-simulated mean and variance of cloudy updraft properties, as well as the response of convection to temperature/moisture perturbations.

scholarly journals Automated tracking of shallow cumulus clouds in large domain, long duration Large Eddy Simulations

2013 ◽  
Vol 6 (2) ◽  
pp. 2287-2323 ◽  
Author(s):  
T. Heus ◽  
A. Seifert
Keyword(s):  
Large Data ◽  
Current Method ◽  
Large Eddy Simulations ◽  
Large Data Sets ◽  
Data Sets ◽  
Cumulus Clouds ◽  
3 Dimensional ◽  
Shallow Cumulus ◽  
Long Duration ◽  
Large Eddy

Abstract. This paper presents a method for feature tracking of fields of shallow cumulus convection in Large Eddy Simulations (LES) by connecting the projected cloud cover in space and time, and by accounting for splitting and merging of cloud objects. Existing methods tend to be either imprecise or, when using the full 3 dimensional spatial field, prohibitively expensive for large data sets. Compared to those 3-D methods, the current method reduces the memory footprint by up to a factor 100, while retaining most of the precision by correcting for splitting and merging events between different clouds. The precision of the algorithm is further enhanced by taking the vertical extent of the cloud into account. Furthermore, rain and subcloud thermals are also tracked, and links between clouds, their rain, and their subcloud thermals are made. The method compares well with results from the literature. Resolution and domain dependencies are also discussed. For the current simulations, the cloud size distribution converges for clouds larger than an effective resolution of 6Δx, and smaller than about 20% of the horizontal domains size.

A study of shallow cumulus cloud droplet dispersion by large eddy simulations

2011 ◽  
Vol 25 (2) ◽  
pp. 166-175 ◽  
Author(s):  
Xiaofeng Wang ◽  
Huiwen Xue ◽  
Wen Fang ◽  
Guoguang Zheng
Keyword(s):  
Cloud Droplet ◽  
Large Eddy Simulations ◽  
Cumulus Cloud ◽  
Droplet Dispersion ◽  
Shallow Cumulus ◽  
Large Eddy

scholarly journals Cloud droplet growth in shallow cumulus clouds considering 1-D and 3-D thermal radiative effects

2019 ◽  
Vol 19 (9) ◽  
pp. 6295-6313 ◽  
Author(s):  
Carolin Klinger ◽  
Graham Feingold ◽  
Takanobu Yamaguchi
Keyword(s):  
Thermal Radiation ◽  
Three Dimensional ◽  
Cloud Droplet ◽  
Large Eddy Simulations ◽  
Droplet Growth ◽  
Radiative Effects ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Thermal Cooling

Abstract. The effect of 1-D and 3-D thermal radiation on cloud droplet growth in shallow cumulus clouds is investigated using large eddy simulations with size-resolved cloud microphysics. A two-step approach is used for separating microphysical effects from dynamical feedbacks. In step one, an offline parcel model is used to describe the onset of rain. The growth of cloud droplets to raindrops is simulated with bin-resolved microphysics along previously recorded Lagrangian trajectories. It is shown that thermal heating and cooling rates can enhance droplet growth and raindrop production. Droplets grow to larger size bins in the 10–30 µm radius range. The main effect in terms of raindrop production arises from recirculating parcels, where a small number of droplets are exposed to strong thermal cooling at cloud edge. These recirculating parcels, comprising about 6 %–7 % of all parcels investigated, make up 45 % of the rain for the no-radiation simulation and up to 60 % when 3-D radiative effects are considered. The effect of 3-D thermal radiation on rain production is stronger than that of 1-D thermal radiation. Three-dimensional thermal radiation can enhance the rain amount up to 40 % compared to standard droplet growth without radiative effects in this idealized framework. In the second stage, fully coupled large eddy simulations show that dynamical effects are stronger than microphysical effects, as far as the production of rain is concerned. Three-dimensional thermal radiative effects again exceed one-dimensional thermal radiative effects. Small amounts of rain are produced in more clouds (over a larger area of the domain) when thermal radiation is applied to microphysics. The dynamical feedback is shown to be an enhanced cloud circulation with stronger subsiding shells at the cloud edges due to thermal cooling and stronger updraft velocities in the cloud center. It is shown that an evaporation–circulation feedback reduces the amount of rain produced in simulations where 3-D thermal radiation is applied to microphysics and dynamics, in comparison to where 3-D thermal radiation is only applied to dynamics.

scholarly journals Evaluation of large-eddy simulations forced with mesoscale model output for a multi-week period during a measurement campaign

2017 ◽  
Vol 17 (11) ◽  
pp. 7083-7109 ◽  
Author(s):  
Rieke Heinze ◽  
Christopher Moseley ◽  
Lennart Nils Böske ◽  
Shravan Kumar Muppa ◽  
Vera Maurer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mesoscale Model ◽  
Large Eddy Simulations ◽  
Model Output ◽  
Synoptic Scale ◽  
High Definition ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Lidar Measurements ◽  
The Mean

Abstract. Large-eddy simulations (LESs) of a multi-week period during the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE) conducted in Germany are evaluated with respect to mean boundary layer quantities and turbulence statistics. Two LES models are used in a semi-idealized setup through forcing with mesoscale model output to account for the synoptic-scale conditions. Evaluation is performed based on the HOPE observations. The mean boundary layer characteristics like the boundary layer depth are in a principal agreement with observations. Simulating shallow-cumulus layers in agreement with the measurements poses a challenge for both LES models. Variance profiles agree satisfactorily with lidar measurements. The results depend on how the forcing data stemming from mesoscale model output are constructed. The mean boundary layer characteristics become less sensitive if the averaging domain for the forcing is large enough to filter out mesoscale fluctuations.

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