Effects of 3D Thermal Radiation on Cloud Development

Abstract. We investigate the effects of thermal radiation on cloud development in an idealized setup in large-eddy simulations with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) and a large cumulus cloud field at 50 m horizontal resolution. We compare the newly developed 3D "neighboring column approximation" with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom, and in the case of a 3D scheme, also cloud side cooling. 3D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (interactive thermal radiation) in a first simulation. Furthermore, a slab-averaged applications of the 1D and 3D radiation is used to study the effect of local cloud radiation as opposed to the domain averaged effect. These simulations exhibit a cooling profile, with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K/d. For the simulations of isolated single cloud, or the cumulus cloud field with interactive radiation, we find that thermal radiation changes cloud circulation, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation we find that interactive radiation, acting locally on clouds enhances the circulation compared to the averaged radiation applications. In addition we find that thermal radiation triggers the organization of clouds. Comparing the effects of 3D and 1D thermal radiation, we find that organization effects of 3D thermal radiation are usually stronger than the 1D counterpart (either interactive or averaged). Interactive radiation leads to an earlier onset of the organization both in 1D and 3D compared to the averaged radiation application. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Interactive thermal radiation produces larger clouds with longer lifetimes.

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Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5477-2017 ◽

2017 ◽

Vol 17 (8) ◽

pp. 5477-5500 ◽

Cited By ~ 18

Author(s):

Carolin Klinger ◽

Bernhard Mayer ◽

Fabian Jakub ◽

Tobias Zinner ◽

Seung-Bu Park ◽

...

Keyword(s):

Thermal Radiation ◽

Radiation Effects ◽

Horizontal Resolution ◽

Surface Fluxes ◽

Cumulus Cloud ◽

Local Cooling ◽

Local Effects ◽

Heating And Cooling ◽

Shallow Cumulus ◽

Local Radiation

Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day−1. To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations. Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes. The cloud fields in the 100 and 50 m resolution simulations develop similarly; however, 3-D local effects are stronger in the 100 m simulations which might indicate a limit of our 3-D radiation parameterization.

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Shallow cumulus cloud feedback in large eddy simulations – bridging the gap to storm-resolving models

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3275-2021 ◽

2021 ◽

Vol 21 (5) ◽

pp. 3275-3288

Author(s):

Jule Radtke ◽

Thorsten Mauritsen ◽

Cathy Hohenegger

Keyword(s):

Cloud Cover ◽

Horizontal Resolution ◽

Cloud Fraction ◽

Cloud Feedback ◽

Cloud Base ◽

Trade Wind ◽

Cumulus Cloud ◽

Shallow Cumulus ◽

Large Eddy ◽

Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty in projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Nonhydrostatic Large Eddy Model in a control and a perturbed 4 K warmer climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened, the base-state cloud fraction increases substantially, especially near cloud base, lateral mixing is weaker, and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of base-state cloud fraction and thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapour availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm-resolving models may exaggerate the trade wind cumulus cloud feedback.

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Shallow Cumulus Cloud Feedback in Large Eddy Simulations – Bridging the Gap to Storm Resolving Models

10.5194/acp-2020-1160 ◽

2020 ◽

Author(s):

Jule Radtke ◽

Thorsten Mauritsen ◽

Cathy Hohenegger

Keyword(s):

Cloud Cover ◽

Horizontal Resolution ◽

Cloud Fraction ◽

Cloud Feedback ◽

Cloud Base ◽

Trade Wind ◽

Cumulus Cloud ◽

Shallow Cumulus ◽

Large Eddy ◽

Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty to interpretations and projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Non-hydrostatic Large Eddy Model in a control and a perturbed 4 K warmed climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened the basic state cloud fraction increases substantially, especially at cloud base, lateral mixing is weaker and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of basic state cloud fraction, thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapor availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm resolving models may exaggerate the trade wind cumulus cloud feedback.

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Thermal structure of intense convective clouds derived from GPS radio occultations

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-5309-2012 ◽

2012 ◽

Vol 12 (12) ◽

pp. 5309-5318 ◽

Cited By ~ 34

Author(s):

R. Biondi ◽

W. J. Randel ◽

S.-P. Ho ◽

T. Neubert ◽

S. Syndergaard

Keyword(s):

Thermal Structure ◽

Deep Convection ◽

Lapse Rate ◽

Orthogonal Polarization ◽

Cold Temperatures ◽

Temperature Lapse Rate ◽

Convective Systems ◽

Convective Clouds ◽

Strong Inversion ◽

Cloud Tops

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

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Size Statistics of Cumulus Cloud Populations in Large-Eddy Simulations

Journal of the Atmospheric Sciences ◽

10.1175/1520-0469(2003)60<1060:ssoccp>2.0.co;2 ◽

2003 ◽

Vol 60 (8) ◽

pp. 1060-1074 ◽

Cited By ~ 76

Author(s):

R. A. J. Neggers ◽

H. J. J. Jonker ◽

A. P. Siebesma

Keyword(s):

Large Eddy Simulations ◽

Cumulus Cloud ◽

Large Eddy

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The influence of the non-resolved scales of thermal radiation in large eddy simulation of turbulent flows: A fundamental study

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2010.02.002 ◽

2010 ◽

Vol 53 (13-14) ◽

pp. 2897-2907 ◽

Cited By ~ 31

Author(s):

Maxime Roger ◽

Pedro J. Coelho ◽

Carlos B. da Silva

Keyword(s):

Large Eddy Simulation ◽

Thermal Radiation ◽

Turbulent Flows ◽

Fundamental Study ◽

Eddy Simulation ◽

Large Eddy

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Larger-Eddy Simulation of Velocity Fluctuation in a Mixing T-Junction

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.152-154.1313 ◽

2012 ◽

Vol 152-154 ◽

pp. 1313-1318

Author(s):

Tao Lu ◽

Su Mei Liu ◽

Ping Wang ◽

Wei Yyu Zhu

Keyword(s):

Experimental Data ◽

Velocity Fluctuation ◽

Flow Model ◽

Numerical Results ◽

Mean Square ◽

Main Duct ◽

Velocity Fluctuations ◽

Eddy Simulation ◽

Large Eddy ◽

Les Model

Velocity fluctuations in a mixing T-junction were simulated in FLUENT using large-eddy simulation (LES) turbulent flow model with sub-grid scale (SGS) Smagorinsky–Lilly (SL) model. The normalized mean and root mean square velocities are used to describe the time-averaged velocities and the velocities fluctuation intensities. Comparison of the numerical results with experimental data shows that the LES model is valid for predicting the flow of mixing in a T-junction junction. The numerical results reveal the velocity distributions and fluctuations are basically symmetrical and the fluctuation at the upstream of the downstream of the main duct is stronger than that at the downstream of the downstream of the main duct.

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Demistify: a large-eddy simulation (LES) and single-column model (SCM) intercomparison of radiation fog

Atmospheric Chemistry and Physics ◽

10.5194/acp-22-319-2022 ◽

2022 ◽

Vol 22 (1) ◽

pp. 319-333

Author(s):

Ian Boutle ◽

Wayne Angevine ◽

Jian-Wen Bao ◽

Thierry Bergot ◽

Ritthik Bhattacharya ◽

...

Keyword(s):

Large Eddy Simulation ◽

Weather Prediction ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Radiation Fog ◽

Eddy Simulation ◽

Cloud Droplet Size Distribution ◽

Large Eddy ◽

Single Column ◽

Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the Local and Non-local Fog Experiment (LANFEX) field campaign. Seven of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst three are research-grade SCMs designed for fog simulation, and the LESs are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number concentration (CDNC) conditions. The main SCM bias appears to be toward the overdevelopment of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parameterisation, as it is to the underlying aerosol or CDNC.

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The Lagrangian ice microphysics code LCM: Introduction, current developments and benefits

10.5194/egusphere-egu2020-2307 ◽

2020 ◽

Author(s):

Simon Unterstrasser

Keyword(s):

Crystal Growth ◽

Turbulent Dispersion ◽

Eddy Simulation ◽

Ice Nuclei ◽

Large Eddy ◽

Radiative Impact ◽

Ice Microphysics ◽

Microphysical Processes ◽

Aerosol Module ◽

Les Model

The Lagrangian Cirrus Module (LCM) is a Lagrangian (also known as particle-based) ice microphysics code that is fully coupled to the large-eddy simulation (LES) code EULAG. The ice phase is described by a large number of simulation particles (order 106 to109) which act as surrogates for the real ice crystals. The simulation particles (SIPs) are advected and microphysical processes like deposition/sublimation and sedimentation are solved for each individual SIP. More specifically, LCM treats ice nucleation, crystal growth, sedimentation, aggregation, latent heat release, radiative impact on crystal growth, and turbulent dispersion. The aerosol module comprises an explicit representation of size-resolved non-equilibrium aerosol microphysical processes for supercooled solution droplets and insoluble ice nuclei.First, an general introduction to particle-based microphysics coupled to a grid-based (Eulerian) LES model is given. In the following, emphasis is put on highlighting the benefits of the Lagrangian approach by presenting a variety of simulation examples.

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