scholarly journals Cloud Droplet Growth in Shallow Cumulus Clouds Considering 1D and 3D Thermal Radiative Effects

2018 ◽  
Author(s):  
Carolin Klinger ◽  
Graham Feingold ◽  
Takanobu Yamaguchi
Keyword(s):  
Thermal Radiation ◽  
Rain Rate ◽  
Cloud Droplet ◽  
Large Eddy Simulations ◽  
Droplet Growth ◽  
Radiative Effects ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Thermal Cooling

Abstract. The effect of 1D and 3D 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 with bin resolved microphysics is used where cloud droplets are grown along previously recorded Lagrangian trajectories. It is shown that thermal heating and cooling rates can enhance droplet growth and rain production. Droplets grow to larger size bins in the 10–30 μm radius range. The main effect in terms of rain production arises from recirculating parcels, where a small number of droplets is exposed to strong thermal cooling at cloud edge. These recirculating parcels, comprising about 6–7 % of all parcels investigated, make up 45 % of the accumulated rain rate for the no radiation simulation and up to 60 % when 3D radiative effects are considered. The effect of 3D thermal radiation on rain production is stronger than that of 1D thermal radiation. 3D thermal radiation can enhance the rain rate 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. 3D thermal radiative effects again exceed 1D 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 3D thermal radiation is applied to microphysics and dynamics, in comparison where 3D thermal radiation is only applied to dynamics.

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 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

On the lifecycle of a shallow cumulus cloud: Is it a bubble or plume, active or forced?

2021 ◽  
Author(s):  
David M. Romps ◽  
Rusen Öktem ◽  
Satoshi Endo ◽  
Andrew M. Vogelmann
Keyword(s):  
Cloud Cover ◽  
Large Eddy Simulations ◽  
The Other ◽  
Doppler Lidar ◽  
Cumulus Cloud ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Stereo Cameras ◽  
Using Data

AbstractA cloud’s lifecycle determines how its mass flux translates into cloud cover, thereby setting Earth’s albedo. Here, an attempt is made to quantify the most basic aspects of the lifecycle of a shallow cumulus cloud: the degree to which it is a bubble or plume, and active or forced. Quantitative measures are proposed for these properties, which are then applied to hundreds of shallow cumulus clouds in Oklahoma using data from stereo cameras, a Doppler lidar, and large-eddy simulations. The observed clouds are intermediate between active and forced, but behave more like bubbles than plumes. The simulated clouds, on the other hand, are more active and plume-like, suggesting room for improvement in the modeling of shallow cumulus.

scholarly journals Automated tracking of shallow cumulus clouds in large domain, long duration large eddy simulations

2013 ◽  
Vol 6 (4) ◽  
pp. 1261-1273 ◽  
Author(s):  
T. Heus ◽  
A. Seifert
Keyword(s):  
Three Dimensional ◽  
Domain Size ◽  
Large Data ◽  
Current Method ◽  
Large Eddy Simulations ◽  
Data Sets ◽  
Cumulus Clouds ◽  
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 three-dimensional (3-D) 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 6 times the horizontal grid spacing, and smaller than about 20% of the horizontal domain size.

scholarly journals Vertical transport of pollutants by shallow cumuli from large eddy simulations

2012 ◽  
Vol 12 (23) ◽  
pp. 11319-11327 ◽  
Author(s):  
G. Chen ◽  
H. Xue ◽  
G. Feingold ◽  
X. Zhou
Keyword(s):  
Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Vertical Transport ◽  
Large Eddy Simulations ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Upward Transport ◽  
Lower Boundary Layer

Abstract. This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. Cumulus convection is therefore able to both vent pollutants upward from the surface and fumigate pollutants in the inversion layer downward into the lower boundary layer.

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 Vertical transport of pollutants by shallow cumuli from large eddy simulations

2012 ◽  
Vol 12 (5) ◽  
pp. 11391-11413
Author(s):  
G. Chen ◽  
H. Xue ◽  
G. Feingold ◽  
X. Zhou
Keyword(s):  
Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Vertical Transport ◽  
Large Eddy Simulations ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Dry Convection ◽  
Lower Boundary Layer

Abstract. This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. We also preformed cloud-free sensitivity runs for the two cases. Results show that this dry convection can neither transport the surface-borne pollutants into the inversion layer, nor transport pollutants from the inversion layer downward to the lower boundary layer. Cumulus convection is therefore more effective than dry convection at venting pollutants upward from the surface, and fumigating pollutants in the inversion layer downward into the lower boundary layer.

Broadening of the Cloud Droplet Size Distribution due to Thermal Radiative Cooling: Turbulent Parcel Simulations

2020 ◽  
Vol 77 (6) ◽  
pp. 1993-2010
Author(s):  
Mares Barekzai ◽  
Bernhard Mayer
Keyword(s):  
Thermal Radiation ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Growth Efficiency ◽  
Droplet Growth ◽  
Radiative Cooling ◽  
Radiative Effect ◽  
Diffusional Growth ◽  
The Impact

Abstract Despite impressive advances in rain forecasts over the past decades, our understanding of rain formation on a microphysical scale is still poor. Droplet growth initially occurs through diffusion and, for sufficiently large radii, through the collision of droplets. However, there is no consensus on the mechanism to bridge the condensation coalescence bottleneck. We extend the analysis of prior methods by including radiatively enhanced diffusional growth (RAD) to a Markovian turbulence parameterization. This addition increases the diffusional growth efficiency by allowing for emission and absorption of thermal radiation. Specifically, we quantify an upper estimate for the radiative effect by focusing on droplets close to the cloud boundary. The strength of this simple model is that it determines growth-rate dependencies on a number of parameters, like updraft speed and the radiative effect, in a deterministic way. Realistic calculations with a cloud-resolving model are sensitive to parameter changes, which may cause completely different cloud realizations and thus it requires considerable computational power to obtain statistically significant results. The simulations suggest that the addition of radiative cooling can lead to a doubling of the droplet size standard deviation. However, the magnitude of the increase depends strongly on the broadening established by turbulence, due to an increase in the maximum droplet size, which accelerates the production of drizzle. Furthermore, the broadening caused by the combination of turbulence and thermal radiation is largest for small updrafts and the impact of radiation increases with time until it becomes dominant for slow synoptic updrafts.

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