An entraining jet model for cumulo-nimbus updraughts

Squires, P.; Turner, J. S.

doi:10.1111/j.2153-3490.1962.tb01355.x

Cited by 54 publications

(27 citation statements)

References 12 publications

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“…On the other hand, for small clouds, being about as deep as wide, a nonsteady bubble model seemed more appropriate in which the air in the wake near the top will be the dominant mixing process. In line with the current general view, Squires and Turner (1962) presumed that a realistic model of cumulus convection should include features of both models. Nevertheless, contemporary convection schemes mainly possess the characteristics of a plume model.…”

Section: Thermal or Plume?mentioning

confidence: 81%

“…However, it turned out to be a challenging subject since some of the fundamental questions related to it are still a matter of debate. This applies, for instance, to the question of whether cumulus convection should be represented by a bubble or a plume, a topic already discussed by Squires and Turner (1962), and also to whether the dilution of the cloudy updraught is predominantly caused by lateral or cloud-top entrainment. Furthermore, whereas early studies concentrated more on the mixing of a single cloud, nowadays due to its application in parametrisations in NWP and climate models there is a need to describe the effect of lateral mixing for a whole cumulus ensemble.…”

Section: Historymentioning

confidence: 99%

“…As mentioned above, Squires and Turner (1962) discussed the differences between the plume or jet and the bubble as a thermal concept for describing convection. Looking at a large thunderstorm with its rather tall and slender current, they suggested an analogy with a steady-state buoyant turbulent plume, having a continuous source of heat from below cloud base and no significant mixing at cloud top.…”

Section: Thermal or Plume?mentioning

confidence: 99%

See 2 more Smart Citations

Entrainment and detrainment in cumulus convection: an overview

Rooy

Bechtold

Fröhlich

et al. 2012

Quart J Royal Meteoro Soc

293

256

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Entrainment and detrainment processes have been recognised for a long time as key processes for cumulus convection and have recently witnessed a regrowth of interest mainly due to the capability of large-eddy simulations (LES) to diagnose these processes in more detail. This article has a twofold purpose. Firstly, it provides a historical overview of the past research on these mixing processes, and secondly, it highlights more recent important developments. These include both fundamental process studies using LES aiming to improve our understanding of the mixing process, but also more practical studies targeted toward an improved parametrised representation of entrainment and detrainment in large-scale models. A highlight of the fundamental studies resolves a long-lasting controversy by showing that lateral entrainment is the dominant mixing mechanism in comparison with the cloud-top entrainment in shallow cumulus convection. The more practical studies provide a wide variety of new parametrisations with sometimes conflicting approaches to the way in which the effect of the free tropospheric humidity on the lateral mixing is taken into account. An important new insight that will be highlighted is that, despite the focus in the literature on entrainment, it appears that it is rather the detrainment process that determines the vertical structure of the convection in general and the mass flux especially. Finally, in order to speed up progress and stimulate convergence in future parametrisations, stronger and more systematic use of LES is advocated.

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Section: Thermal or Plume?mentioning

confidence: 81%

Section: Historymentioning

confidence: 99%

Section: Thermal or Plume?mentioning

confidence: 99%

See 1 more Smart Citation

Entrainment and detrainment in cumulus convection: an overview

Rooy

Bechtold

Fröhlich

et al. 2012

Quart J Royal Meteoro Soc

293

256

View full text Add to dashboard Cite

show abstract

“…This consistency requirement is valuable because entrainment models -which make particular assumptions regarding β g , θ m and γ g -have received criticism for not being applicable to specific flows, e.g. for clouds (Squires & Turner 1962) or for reacting plumes (Ricou & Spalding 1961;Hermanson & Dimotakis 1989). Indeed, the attractiveness of (3.1) is that it is a relation with which all models for entrainment must be consistent.…”

Section: The Entrainment Relationmentioning

confidence: 99%

Energy-consistent entrainment relations for jets and plumes

2015

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We discuss energetic restrictions on the entrainment coefficient α for axisymmetric jets and plumes. The resulting entrainment relation includes contributions from the mean flow, turbulence and pressure, fundamentally linking α to the production of turbulence kinetic energy, the plume Richardson number Ri and the profile coefficients associated with the shape of the buoyancy and velocity profiles. This entrainment relation generalises the work by Kaminski et al. (J. Fluid Mech., vol. 526, 2005, pp. 361-376) and Fox (J. Geophys. Res., vol. 75, 1970, pp. 6818-6835). The energetic viewpoint provides a unified framework with which to analyse the classical entrainment models implied by the plume theories of Morton et al. , vol. 81, 1954, pp. 144-157). Data for pure jets and plumes in unstratified environments indicate that to first order the physics is captured by the Priestley and Ball entrainment model, implying that (1) the profile coefficient associated with the production of turbulence kinetic energy has approximately the same value for pure plumes and jets, (2) the value of α for a pure plume is roughly a factor of 5/3 larger than for a jet and (3) the enhanced entrainment coefficient in plumes is primarily associated with the behaviour of the mean flow and not with buoyancy-enhanced turbulence. Theoretical suggestions are made on how entrainment can be systematically studied by creating constant-Ri flows in a numerical simulation or laboratory experiment.

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“…This approach was adapted to modelling entrainment in cumulus clouds (e.g. Morton, 1957;Squires and Turner, 1962) but was less successful for clouds than for dry plumes. Clearly, the latent heating and evaporative cooling that occur within clouds either provide or remove energy that affect the cloud dynamics.…”

Section: Entrainment In Cumulus Cloudsmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

243

281

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In this survey we consider the impact of turbulence on cloud formation from the cloud scale to the droplet scale. We assess progress in understanding the effect of turbulence on the condensational and collisional growth of droplets and the effect of entrainment and mixing on the droplet spectrum. The increasing power of computers and better experimental and observational techniques allow for a much more detailed study of these processes than was hitherto possible. However, much of the research necessarily remains idealized and we argue that it is those studies which include such fundamental characteristics of clouds as droplet sedimentation and latent heating that are most relevant to clouds. Nevertheless, the large body of research over the last decade is beginning to allow tentative conclusions to be made. For example, it is unlikely that small-scale turbulent eddies (i.e. not the energy-containing eddies) alone are responsible for broadening the droplet size spectrum during the initial stage of droplet growth due to condensation. It is likely, though, that small-scale turbulence plays a significant role in the growth of droplets through collisions and coalescence. Moreover, it has been possible through detailed numerical simulations to assess the relative importance of different processes to the turbulent collision kernel and how this varies in the parameter space that is important to clouds. The focus of research on the role of turbulence in condensational and collisional growth has tended to ignore the effect of entrainment and mixing and it is arguable that they play at least as important a role in the evolution of the droplet spectrum. We consider the role of turbulence in the mixing of dry and cloudy air, methods of quantifying this mixing and the effect that it has on the droplet spectrum. Copyright

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An entraining jet model for cumulo-nimbus updraughts

Cited by 54 publications

References 12 publications

Entrainment and detrainment in cumulus convection: an overview

Entrainment and detrainment in cumulus convection: an overview

Energy-consistent entrainment relations for jets and plumes

Droplet growth in warm turbulent clouds

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