Multidimensional Longwave Forcing of Boundary Layer Cloud Systems

Mechem, David B.; Kogan, Yefim L.; Ovtchinnikov, Mikhail; Davis, Anthony B.; Evans, K. Franklin; Ellingson, Robert G.

doi:10.1175/2008jas2733.1

Cited by 8 publications

(6 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is a similar result to Mechem et al (2008) where differences between 1-D and 3-D thermal radiative transfer in a shallow cumulus cloud field were small as well. We will address the issue of these small differences between the 1-D and 3-D local radiation simulations in Sect.…”

Section: Summary Of Cloud Developmentsupporting

confidence: 87%

See 1 more Smart Citation

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

et al. 2017

View full text Add to dashboard Cite

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...

show abstract

Section: Summary Of Cloud Developmentsupporting

confidence: 87%

“…At the end of their simulation, Guan et al (1997) found an acceleration of the dissipation of the cloud with thermal radiation. Mechem et al (2008) coupled the 3-D radiative transfer model SHDOM (Evans, 1998) to a 2-D cloud model. The ef-fects of 3-D thermal radiative transfer on stratocumulus and isolated shallow cumulus were studied.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Stephens et al, 1991;Barker et al, 2003a). While many have shown that differences between local and area-averaged fluxes produced by ICA and 3D RTMs can be large for some cloudy atmospheres (see several chapters in Marshak and Davis, 2005a), only a handful of CSRM experimental simulations have used 3D RT models interactively (Guan et al, 1997;Mechem et al, 2008;Jakub and Mayer, 2017;Klinger et al, 2017). It is widely recognized that the computational demands of 3D RTMs outweigh, for now at least, any scientific benefits they might afford, thereby amounting to (temporary) tacit acceptance of the ICA.…”

Section: Introductionmentioning

confidence: 99%

Accelerating radiative transfer calculations for high‐resolution atmospheric models

Barker

2019

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

This study presents a method for calculating all‐sky, broadband radiative fluxes for high‐resolution atmospheric model domains, such as limited‐area numerical weather prediction models and Cloud System‐Resolving Models, that have many columns (i.e. N ≫ 105). The aim is to replace the Independent Column Approximation (ICA) which applies 1D radiative transfer models (RTMs) to all N columns; but usually after skipping many dynamical time steps due to the ICA's computational burden. The proposed method, referred to as Partitioned Gauss–Legendre Quadrature (PGLQ), begins by partitioning a domain into M sub‐domains. This study is concerned just with cloudy columns so partitioning was done according to cloud‐top altitudes. Then, for each sub‐domain, sort columns from smallest to largest cloud water path W, assign each column a sequence number, identify nG GLQ points, and apply 1D RTMs to the nG columns with resulting flux profiles assigned to nearby columns in the sorted sequence. Last, reposition columns back to the full domain. Marine boundary‐layer and deep convective cloud fields were used to assess PGLQ. For ratios of RTM calculations between ICA and PGLQ of fRT = N/(nG · M)−1 ∈ [103, 104], MBEs and RMSEs for net short‐wave (SW) surface fluxes FnormalSWNETSFC scale close to (nG · M)−1, RMSEs being typically ∼200× smaller than domain‐average FnormalLWNETSFC. Structure function analyses of FnormalSWNETSFC indicate that PGLQ errors resemble white noise. Long‐wave (LW) fluxes perform less well due to sorting on W but seem likely to be acceptable, RMSEs being ∼5–10× smaller than domain‐average FnormalSWNETSFC. All MBEs are typically <±0.5 W/m2. Estimates of radiative heating rate profiles are unbiased, and while noisy at small scales, they are portrayed well at scales larger than typical individual clouds. Overall speed‐up of PGLQ relative to ICA, for serial computation as consider here, is expected to be >300×; likely to be comparable to parallel computation. This should allow application of RTMs at every dynamical time step.

show abstract

“…At the end of the study, we will briefly investigate thermal radiative effects on dynamics as e.g. shown by Klinger et al (2017), Guan et al (1995Guan et al ( , 1997 or Mechem et al (2008).…”

mentioning

confidence: 99%

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

Klinger¹,

Feingold²,

Yamaguchi³

2018

Preprint

View full text Add to dashboard Cite

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&#8211;30&#8201;&#956;m 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&#8211;7&#8201;% of all parcels investigated, make up 45&#8201;% of the accumulated rain rate for the no radiation simulation and up to 60&#8201;% 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&#8201;% 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.

show abstract

Multidimensional Longwave Forcing of Boundary Layer Cloud Systems

Cited by 8 publications

References 40 publications

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

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

Accelerating radiative transfer calculations for high‐resolution atmospheric models

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

Contact Info

Product

Resources

About