Turbulent collision efficiency of heavy particles relevant to cloud droplets

Wang, Lian‐Ping; Ayala, Orlando; Rosa, Bogdan; Grabowski, Wojciech W.

doi:10.1088/1367-2630/10/7/075013

Cited by 84 publications

(116 citation statements)

References 27 publications

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“…This shows that different approaches appear to lead to similar levels of enhancement factors by air turbulence. The values shown in Figure 2 should be taken as preliminary results owing to the limitations of DNS, as noted in Pinsky et al (2007), Ayala et al (2008a) and Wang et al (2008). The most significant limitation is that not all scales of turbulence affecting droplet-droplet interactions are included in DNS, making the enhancement factors shown in Figure 2 most likely a lower bound of what might occur in real clouds.…”

Section: Impact Of Turbulent Collision-coalescence On Droplet Growthmentioning

confidence: 99%

“…Nevertheless, it is likely that only through successively more complex but still relatively idealized studies will it be possible to distinguish those physical processes which play a key role in cloud formation and precipitation, and which need to be included in parametrizations of cloud microphysics, from processes which can be regarded as being of secondary importance. An example is DNS of sedimenting cloud droplets (Franklin et al, 2007;Ayala et al, 2008a;Wang et al, 2008) which provided quantitative data on turbulent enhancement of the collision kernel and, more importantly, on the relative contributions to this enhancement from the effects of turbulence on the relative velocity of the droplets, preferential concentration and collision efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

239

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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Section: Impact Of Turbulent Collision-coalescence On Droplet Growthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

239

281

View full text Add to dashboard Cite

show abstract

“…The overall conclusion is that η T is moderate but it occurs at the right places, that is, where the hydrodynamicgravitational collection kernel tends to be relatively small. Complete compilations and discussions of the simulation results are found in Ayala et al (2008b) and Wang et al (2008) …”

Section: Turbulent Enhancementmentioning

confidence: 99%

“…Therefore, our parameterization of the collection kernel, to certain extent, can represent realistic flow Reynolds numbers in clouds. Moreover, we include the enhancement η E on the collision efficiency by interpolating and extending the tabulated simulation results of η E from Wang et al (2008). Additional simulations at a 2 /a 1 = 0.916 and a 2 /a 1 = 0.0835 were also performed.…”

Section: Impact On Warm Rain Initiationmentioning

confidence: 99%

“…Additional simulations at a 2 /a 1 = 0.916 and a 2 /a 1 = 0.0835 were also performed. Specifically, for each droplet size combination studied, η E is obtained by dividing the turbulent collision efficiency with the collision efficiency in still air, both of which were simulated with our hybrid DNS approach as described in Wang et al (2008). For the case of equal-sized pairs (a 2 /a 1 = 1), the turbulent collision efficiency could depend on the overall droplet number concentration used , in this case, an averaged value was used.…”

Section: Impact On Warm Rain Initiationmentioning

confidence: 99%

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The role of air turbulence in warm rain initiation

Wang

Grabowski

2009

Atmospheric Science Letters

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Quantitative parameterization of turbulent collision of cloud droplets represents a major unsolved problem in cloud physics. Here a hybrid direct simulation tool is used specifically to quantify the turbulent enhancement of the gravitational collision-coalescence. Simulation results show that air turbulence can enhance the collision kernel by an average factor of about 2, and the observed trends are supported by scaling arguments. An impact study using the most realistic collection kernel suggests that cloud turbulence can significantly reduce the time for warm rain initiation. Areas for further development of the hybrid simulation and the impact study are indicated.

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Effects of turbulence‐induced collision enhancement on heavy precipitation: The 21 September 2010 case over the Korean Peninsula

Lee

Baik

2016

JGR Atmospheres

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The effects of turbulence‐induced collision enhancement (TICE) on a heavy precipitation event that occurred on 21 September 2010 over the middle Korean Peninsula are examined. For this purpose, an updated bin microphysics scheme incorporating TICE for drop‐drop and drop‐graupel collisions is implemented into the Weather Research and Forecasting (WRF) model. The numerical simulation shows some differences in the strong precipitation system compared to the observations but generally captures well the important features of observed synoptic conditions, surface precipitation, and radar reflectivity. While the change in domain‐averaged surface precipitation amount due to TICE is small and similar to that due to small initial perturbations, the spatial distribution of surface precipitation amount is somewhat altered due to TICE. The surface precipitation amount is increased due to TICE in the area where the largest surface precipitation occurred, but the effects of different flow realizations also contribute to the changes. TICE accelerates the coalescence between small cloud droplets, which induces a decrease in condensation and an increase in excess water vapor transported upward. This causes an increase in relative humidity with respect to ice at high altitudes, hence increasing the depositional growth of ice particles. Therefore, the ice mass increases due to TICE, and this increase induces the increases in riming and melting of ice particles. A series of these microphysical changes due to TICE are regarded as partially contributing to the increase in surface precipitation amount in some areas, hence inducing alterations in the spatial distribution of surface precipitation amount.

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Turbulent collision efficiency of heavy particles relevant to cloud droplets

Cited by 84 publications

References 27 publications

Droplet growth in warm turbulent clouds

Droplet growth in warm turbulent clouds

The role of air turbulence in warm rain initiation

Effects of turbulence‐induced collision enhancement on heavy precipitation: The 21 September 2010 case over the Korean Peninsula

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