Impact of subgrid‐scale radiative heating variability on the stratocumulus‐to‐trade cumulus transition in climate models

Xiao, Heng; Gustafson, William I.; Wang, Hailong

doi:10.1002/2013jd020999

Cited by 9 publications

(10 citation statements)

References 42 publications

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“…The way the slab average radiation is applied (either calculated from the direct simulation of local effects or from the GCM itself) did not change cloud development in a significant way. The difference between the application of local and homogenized radiation was also addressed by Xiao et al (2014), with a focus on stratocumulus to cumulus transition. Again, an increase in turbulence, due to the destabilization of the clouds by thermal radiation, was found.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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...

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Section: Introductionmentioning

confidence: 99%

“…Again, an increase in turbulence, due to the destabilization of the clouds by thermal radiation, was found. Xiao et al (2014) state that because they only used a common 1-D approximation for the radiation calculation the effects might be larger with 3-D radiation.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…The Weather Research and Forecasting (WRF) model [ Skamarock et al ., ] is a mesoscale numerical weather model designed for atmospheric research and operational forecasting. In recent years, WRF has gained popularity as a large‐eddy simulation (LES) model due to its built‐in nesting capability, its open and modularized structure that facilitates the implementation of new physical parameterizations, and its fully compressible nonhydrostatic dynamic core [e.g., Moeng et al ., ; Wang et al ., ; Wang and Feingold , ; Yamaguchi and Feingold , ; Blossey et al ., ; Yamaguchi et al ., ; Xiao et al ., ; Endo et al ., ].…”

Section: Introductionmentioning

confidence: 98%

Modifications to WRF's dynamical core to improve the treatment of moisture for large‐eddy simulations

Xiao

Endo

Wong

et al. 2015

J Adv Model Earth Syst

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Yamaguchi and Feingold (2012) note that the cloud fields in their large-eddy simulations (LESs) of marine stratocumulus using the Weather Research and Forecasting (WRF) model exhibit a strong sensitivity to time stepping choices. In this study, we reproduce and analyze this sensitivity issue using two stratocumulus cases, one marine and one continental. Results show that (1) the sensitivity is associated with spurious motions near the moisture jump between the boundary layer and the free atmosphere, and (2) these spurious motions appear to arise from neglecting small variations in water vapor mixing ratio (q v ) in the pressure gradient calculation in the acoustic substepping portion of the integration procedure. We show that this issue is remedied in the WRF dynamical core by replacing the prognostic equation for the potential temperature h with one for the moist potential temperature h m 5h(1 1 1.61q v ), which allows consistent treatment of moisture in the calculation of pressure during the acoustic substeps. With this modification, the spurious motions and the sensitivity to the time stepping settings (i.e., the dynamic time step length and number of acoustic sub-steps) are eliminated in both of the example stratocumulus cases. This modification improves the applicability of WRF for LES applications, and possibly other models using similar dynamical core formulations, and also permits the use of longer time steps than in the original code.

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“…Thermal radiation increased turbulence on short time scales, and on longer time scales the cloud development itself. A similar approach was followed by Xiao et al (2014). In this case, simulations with interactive and homogenized radiation where performed, with a focus on stratocumulus to cumulus transition.…”

Section: Introductionmentioning

confidence: 99%

“…Again, an increase in turbulence, due to the 25 destabilization of the clouds by thermal radiation was found. Xiao et al (2014) state that because they only used a common 1D approximation for the radiation calculation the effects might be larger with 3D radiation. The hypothesis of destabilization of the cloud layer by thermal radiation was originally proposed by Lilly (1988).…”

Section: Introductionmentioning

confidence: 99%

Effects of 3D Thermal Radiation on Cloud Development

Klinger

Mayer

Jakub

et al. 2016

Preprint

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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&#8201;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&#8201;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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Impact of subgrid‐scale radiative heating variability on the stratocumulus‐to‐trade cumulus transition in climate models

Cited by 9 publications

References 42 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

Modifications to WRF's dynamical core to improve the treatment of moisture for large‐eddy simulations

Effects of 3D Thermal Radiation on Cloud Development

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