Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence

Park, Seung-Bu; Gentine, Pierre; Schneider, Kai; Farge, Marie

doi:10.1175/jas-d-15-0240.1

Cited by 31 publications

(55 citation statements)

References 84 publications

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“…Two passive scalar tracers were implemented into UCLA-LES, following Park et al (2016). With the help of the tracers, we performed an octant analysis (Park et al, 2016) to extract coherent structures in simulation data.…”

Section: Simulation Setupmentioning

confidence: 99%

“…With the help of the tracers, we performed an octant analysis (Park et al, 2016) to extract coherent structures in simulation data. For further analysis of the results, we used the cloud-tracking algorithm Cb-TRAM (Zinner et al, 2008).…”

Section: Simulation Setupmentioning

confidence: 99%

“…Time-averaged profiles of buoyancy production of the turbulent kinetic energy (TKE) and updraft and downdraft vertical velocity.The profiles are shown at the restart time (3 h) as a 3 h average centered at 10 and 20 h of the simulations. Updraft and downdraft vertical velocities were extracted from the 3-D data following Park et al (2016). tions (see Fig. 10) which in turn leads to a higher relative humidity and more condensation of water vapor.…”

Section: Boundary Layer and Cloud Layer Developmentmentioning

confidence: 99%

“…In a detailed study, Petch and Gray (2001) investigated the robustness of cloud simulations with varying horizontal resolutions (2 km, 1 km, 500 m), domain size, microphysical parameterizations and different radiation schemes. They also compared results from a 2-D cloud model and a 3-D cloud model.…”

Section: Introductionmentioning

confidence: 99%

“…Ice and mass flux, as well as the amount of condensed water, increased in the slab-averaged radiation application. Petch and Gray (2001) related this to destabilization due to the averaged cooling in areas where there should be no or less cooling in the local application, causing an increase in depth and the rate of development of the clouds. Overall, there were some differences between the averaged and the local radiation cases, but the larger one was found when comparing the radiation results to the no radiation simulation.…”

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: Simulation Setupmentioning

confidence: 99%

Section: Simulation Setupmentioning

confidence: 99%

Section: Boundary Layer and Cloud Layer Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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Role of convective mixing and evaporative cooling in shallow convection

2017

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Large‐eddy simulations of shallow convection are used to evaluate the role of convective mixing and evaporative cooling in the vertical transport of mass, heat, and moisture in nonprecipitating shallow convection. Evaporative cooling is found to increase mass flux and the magnitude of heat and moisture fluxes, comparing twin large‐eddy simulations with either suppressed or active evaporative cooling. Nonetheless, subsiding shells transport mass downward even when evaporative cooling is suppressed, emphasizing that evaporative cooling is not the primary cause of existence of subsiding shells and accompanied buoyancy reversal. Instead, vertical convective mixing is found to be the primary reason of buoyancy reversal. Evaporative cooling yet accelerates downdrafts (updrafts) in the shell (cloudy) regions as well as increases the cloud cover in the lower cloud layer. The cloudy regions are more humid, and the liquid water potential temperature is lower compared to the evaporative‐cooling‐suppressed experiment. The primary effect of evaporative cooling is thus to increase the updraft core anomalies, thus enhancing vertical turbulent fluxes.

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Formation and maintenance of subsiding shells around non‐precipitating and precipitating cumulus clouds

Savre

2020

Quart J Royal Meteoro Soc

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A shell of subsiding air is generally known to develop around cumulus clouds and shield them from their environment. We seek here to improve our understanding of such shells by (1) revealing the detailed vertical and horizontal structure of shells surrounding both shallow and deeper clouds, and (2) identifying the mechanisms responsible for in-shell subsidence generation and maintenance. To that end, a highresolution Cloud Resolving Model simulation of the shallowto-deep convection transition over a tropical land surface is analysed with an emphasis on the clouds near environment. Shells surrounding shallow and deep clouds are found to possess surprisingly similar characteristics. Important differences are however observed near cloud top where the deepest clouds are associated with stronger subsidence and broader shells. In the convective outflow region, stronger in-shell subsidence coincides with strong buoyancy reversal, but also with strong pressure gradients naturally generated by cloud top vortex dynamics. A more delicate balance between various processes takes place below, and in-shell subsidence is only barely sustained as buoyancy reversal is largely compensated by pressure gradients. Finally, while evaporation is clearly the main source of buoyancy reversal (and therefore subsidence) everywhere around cloud edges, it is also shown that the downward transport of warmer air

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Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence

Cited by 31 publications

References 84 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

Role of convective mixing and evaporative cooling in shallow convection

Formation and maintenance of subsiding shells around non‐precipitating and precipitating cumulus clouds

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