Turbulent Diffusion of Heavy Particles in the Atmosphere

Csanady, G. T.

doi:10.1175/1520-0469(1963)020<0201:tdohpi>2.0.co;2

Cited by 508 publications

(334 citation statements)

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“…Sedimenting (inertial) droplets can bias their trajectories towards regions of downward fluid motion around vortices: the crossing-trajectory effect (which occurs primarily because of sedimentation; Csanady, 1963) causes the particle to be preferentially swept to the downward side of the vortex and hence the mean effect of turbulence is a net force that accelerates the particle downwards. The increased settling occurs for Sv 1 and a certain range of τ p (Wang and Maxey, 1993;Dávila and Hunt, 2001).…”

Section: Preferential Sweepingmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

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: Preferential Sweepingmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

281

View full text Add to dashboard Cite

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“…This is strictly valid only when the insect is moving with the air but it is approximately correct when the insect is 'crossing' through the air parcel trajectories. This is because although the so-called 'crossing trajectory effect' (Csanady 1963) will cause the velocities of successive air parcels encountered by the insect to correlate faster than otherwise would be the case, we find that our model predictions are not sensitively dependent upon T.…”

Section: Description Of the Vertical Components Of Turbulent Flowmentioning

confidence: 99%

Does a ‘turbophoretic’ effect account for layer concentrations of insects migrating in the stable night-time atmosphere?

Reynolds

Riley

2008

J. R. Soc. Interface.

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Large migrating insects, such as noctuid moths and acridoid grasshoppers, flying within the stable nocturnal boundary layer commonly become concentrated into horizontal layers. These layers frequently occur near the top of the surface temperature inversion where warm fast-moving airflows provide good conditions for downwind migration. On some occasions, a layer may coincide with a higher altitude temperature maximum such as a subsidence inversion, while on others, it may seem unrelated to any obvious feature in the vertical profile of meteorological variables. Insects within the layers are frequently orientated, either downwind or at an angle to the wind, but the mechanisms involved in both layer formation and common orientation have remained elusive. Here, we show through the results of numerical simulations that if insects are treated as neutrally buoyant particles, they tend to be advected by vertical gusts (through the 'turbophoretic' mechanism) into layers in the atmosphere where the turbulent kinetic energy has local minima. These locations typically coincide with local maxima in the wind speed and/or air temperature, and they may also provide cues for orientation. However, the degree of layering predicted by this model is very much weaker than that observed in the field. We have therefore hypothesized that insects behave in a way that amplifies the turbophoretic effect by initiating climbs or descents in response to vertical gusts. New simulations incorporating this behaviour demonstrated the formation of layers that closely mimic field observations, both in the degree of concentration in layers and the rate at which they form.

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“…We find the largest deviation for the smallest β value, where the bubblerise velocity is largest. The explanation can be sought in the so-called 'crossing trajectory effect' [33,34]: bubble trajectories 'cross' the trajectories of fluid particles, because of the gravity, and therefore rapidly leave those flow regions in which the velocity is highly correlated. The consequence is that the bubble velocity quickly loses the memory of its previous values by sampling flow velocities that are more and more decorrelated.…”

Section: Bubble Diffusionmentioning

confidence: 99%