A Wind Tunnel Study of the Effects of Turbulence on the Growth of Cloud Drops by Collision and Coalescence

Vohl, O.; Mitra, Subir K.; Wurzler, S.; Pruppacher, H. R.

doi:10.1175/1520-0469(1999)056<4088:awtsot>2.0.co;2

Cited by 52 publications

(36 citation statements)

References 24 publications

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“…we can neglect (iii) above). Vohl et al (1999) have conducted wind tunnel experiments which show that this is approximately the case for a < 100 µm (although the experiments were performed at lower Reynolds numbers than are typical of the atmosphere). Droplet growth through collection thus reduces to a problem of determining collision rates.…”

Section: Collisions Coalescence and Turbulencementioning

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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Section: Collisions Coalescence and Turbulencementioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

243

281

View full text Add to dashboard Cite

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“…by Vohl et al [1999]. The broken line shows the droplet size r crit = ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 9rnt k = 2r p r for which the Stokes number with respect to the Kolmogorov timescale is one, with r being the air density and r p the water density.…”

Section: Model Calculationsmentioning

confidence: 99%

“…velocity fluctuations of the tunnel flow. From the experiment, we extract the following information (data reproduced from the original paper by Vohl et al [1999]): 2.2.1. Droplet Size Distribution…”

Section: Model Calculationsmentioning

confidence: 99%

See 1 more Smart Citation

Droplet growth by gravitational coagulation enhanced by turbulence: Comparison of theory and measurements

Riemer¹,

Wexler²,

Diehl³

2007

J. Geophys. Res.

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[1] While it is well known that cloud droplets grow in an inherently turbulent environment, the role of turbulence is only now being elucidated. To shed light on this issue, we compare published measurements of droplet growth by collision in turbulent flow with numerical simulations. Because the measurements demonstrate an accelerated growth under turbulent conditions compared to laminar ones, the data clearly cannot be reproduced using the well-established kernel for sedimentation under laminar conditions. By employing a collision kernel that has been recently derived from direct numerical simulations, we perform sensitivity studies and quantify the parameter ranges that are compatible with the experimental data. This experiment does not enable us to uniquely determine the model parameters but we were able to place constraints on the form of acceptable models that reproduce the experimental data successfully. Moreover, we gain insight into how laboratory experiments could be improved to aid model validation.

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“…Dai (2001b) suggested that diurnal variations in relative humidity (primarily due to the cooler temperatures in the morning) contribute to this morning maximum over land, although he did not elaborate on the mechanism. One hypothesis is that the morning increase in solar insolation produces enough boundary layer and cloud-level turbulence to enhance the collision-coalescence processes that produce drizzle (e.g., Pinsky and Khain 1997;Vohl et al 1999). A second hypothesis may be related to drizzle production in marine stratocumulus when drizzle tends to peak before sunrise.…”

Section: Diurnal Cyclementioning

confidence: 99%

Spatial and Temporal Variability of Nonfreezing Drizzle in the United States and Canada

Sears-Collins

Schultz

Johns³

2006

Journal of Climate

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A climatology of nonfreezing drizzle is created using surface observations from 584 stations across the United States and Canada over the 15-yr period 1976-90. Drizzle falls 50-200 h a year in most locations in the eastern United States and Canada, whereas drizzle falls less than 50 h a year in the west, except for coastal Alaska and several western basins. The eastern and western halves of North America are separated by a strong gradient in drizzle frequency along roughly 100°W, as large as about an hour a year over 2 km. Forty percent of the stations have a drizzle maximum from November to January, whereas only 13% of stations have a drizzle maximum from June to August. Drizzle occurrence exhibits a seasonal migration from eastern Canada and the central portion of the Northwest Territories in summer, equatorward to most of the eastern United States and southeast Canada in early winter, to southeastern Texas and the eastern United States in late winter, and back north to eastern Canada in the spring. The diurnal hourly frequency of drizzle across the United States and Canada increases sharply from 0900 to 1200 UTC, followed by a steady decline from 1300 to 2300 UTC. Diurnal drizzle frequency is at a maximum in the early morning, in agreement with other studies.Drizzle occurs during a wide range of atmospheric conditions at the surface. Drizzle has occurred at sea level pressures below 960 hPa and above 1040 hPa. Most drizzle, however, occurs at higher than normal sea level pressure, with more than 64% occurring at a sea level pressure of 1015 hPa or higher. A third of all drizzle falls when the winds are from the northeast quadrant (360°-89°), suggesting that continental drizzle events tend to be found poleward of surface warm fronts and equatorward of cold-sector surface anticyclones. Two-thirds of all drizzle occurs with wind speeds of 2.0-6.9 m s Ϫ1 , with 7.6% in calm wind and 5% at wind speeds у 10 m s Ϫ1. Most drizzle (61%) occurs with visibilities between 1.5 and 5.0 km, with only about 20% occurring at visibilities less than 1.5 km.

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A Wind Tunnel Study of the Effects of Turbulence on the Growth of Cloud Drops by Collision and Coalescence

Cited by 52 publications

References 24 publications

Droplet growth in warm turbulent clouds

Droplet growth in warm turbulent clouds

Droplet growth by gravitational coagulation enhanced by turbulence: Comparison of theory and measurements

Spatial and Temporal Variability of Nonfreezing Drizzle in the United States and Canada

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