An Improved Approach to Calculating Terminal Velocities of Plate-like Crystals and Graupel

Heymsfield, Andrew J.; Kajikawa, Masahiro

doi:10.1175/1520-0469(1987)044<1088:aiatct>2.0.co;2

Cited by 160 publications

(121 citation statements)

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“…Here, VZ is the fall velocity and * the kinematic viscosity of air. Interrelationships among d(cm), M(g), and VZ(cm s-1) have been described in previous papers (Kajikawa, 1975;Heymsfield and Kajikawa, 1987) for the various shapes of plate-like crystals.…”

Section: 1mentioning

confidence: 72%

Observations of the Falling Motion of Plate-Like Snow Crystals Part I: The Free-Fall Patterns and Velocity

Kajikawa

1992

Journal of the Meteorological Society of Japan

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Free-fall patterns and the variations in the vertical and horizontal velocities of unrimed plate-like snow crystals were analyzed by means of a stereo-photogrammetric method.Whether the crystals exhibit a stable falling motion or not mainly depends on the Best number, which involves the mean vertical velocity (fall velocity), and the non-dimensional moment of inertia of the crystals.Unstable fall patterns were roughly classified into three types: nonrotation, swing, and rotation or spiral. For dendritic shaped crystals, the distinction among these types is approximately determined by the combination of the non-dimensional moment of inertia and the Reynolds number, which involves the mean vertical velocity.Although the standard deviation of the vertical velocity for dendritic shaped crystals was very small (1 to 3% of the mean vertical velocity), that of the horizontal velocity was considerably larger, measuring 5 to 20% of the mean vertical velocity. Accordingly, it appears likely that the variation in the horizontal velocity plays an important role in the random aggregation of plate-like snow crystals having almost the same shape and size.

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Section: 1mentioning

confidence: 72%

Observations of the Falling Motion of Plate-Like Snow Crystals Part I: The Free-Fall Patterns and Velocity

Kajikawa

1992

Journal of the Meteorological Society of Japan

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“…Sassen's (1980) light pillar data indicated that there is likely to be a Reynolds number (Re ≈ 8) where the crystal flutter is minimized, and we expect that these crystals will provide the strongest weighting to the Doppler velocity measurements. Heymsfield and Kajikawa (1987) measured the fall velocity of planar ice crystals collected at the ground in northern Japan (1 km above sea level), and formulated velocity-diameter relationships from their observations. Using the pressure correction method of Beard (1980), we have used these data to calculate the ranges of Reynolds number and crystal diameter corresponding to a fall speed of 0.23 m s −1 for various assumed crystal habits: these values are tabulated in Table III.…”

Section: Vertical Measurementsmentioning

confidence: 99%

“…Note that the radar velocities are larger than measured by the Doppler lidar in the specular ice, reflecting the weighting of the radar towards the heaviest ice particles. The crystal diameter corresponding to this velocity is rather sensitive to the assumed habit, ranging from 800 µm for hexagonal plates to 3500 µm assuming stellars (Heymsfield and Kajikawa, 1987). We note that over the depth of the supercooled layer the reflectivity increases by about 6 dB, which corresponds to a doubling of the average crystal mass over that distance (since reflectivity is, to first order, proportional to mass 2 ), whilst Ryan et al (1976) observed crystal masses to increase by a factor of ten between 50 and 150 s of growth.…”

Section: Vertical Measurementsmentioning

confidence: 99%

“…This is in keeping with the idea that specular reflection is produced by planar crystals from a relatively limited range of Reynolds numbers where the fall orientation is stable and the fall speeds are relatively slow. The corresponding Reynolds numbers for various assumed crystal habits have been calculated using Heymsfield and Kajikawa's (1987) relationships. Segregation of the data by colour ratio (not shown for brevity) shows a slight decrease at the most extreme colour ratios (10-20%); however, this decrease is much smaller than the variation between the different assumed crystal habits (Re ≈ 5 for hexagonal plates versus Re ≈ 20 assuming stellars).…”

Section: Fall Speedsmentioning

confidence: 99%

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Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

Westbrook

Illingworth

O’Connor

et al. 2010

Quart J Royal Meteoro Soc

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The properties of planar ice crystals settling horizontally have been investigated using a vertically pointing Doppler lidar. Strong specular reflections were observed from their oriented basal facets, identified by comparison with a second lidar pointing 4 • from zenith. Analysis of 17 months of continuous high-resolution observations reveals that these pristine crystals are frequently observed in ice falling from mid-level mixed-phase layer clouds (85% of the time for layers at −15 • C). Detailed analysis of a case study indicates that the crystals are nucleated and grow rapidly within the supercooled layer, then fall out, forming well-defined layers of specular reflection. From the lidar alone the fraction of oriented crystals cannot be quantified, but polarimetric radar measurements confirmed that a substantial fraction of the crystal population was well oriented. As the crystals fall into subsaturated air, specular reflection is observed to switch off as the crystal faces become rounded and lose their faceted structure. Specular reflection in ice falling from supercooled layers colder than −22 • C was also observed, but this was much less pronounced than at warmer temperatures: we suggest that in cold clouds it is the small droplets in the distribution that freeze into plates and produce specular reflection, whilst larger droplets freeze into complex polycrystals.The

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“…The LES results depend on the chosen values for ice-microphysical parameters related to ice particle shape, fall velocity, and ice particle mass distribution. The parameters for the reference simulation are selected in such a way that the profiles of cloud liquid water and cloud ice are close to the aircraft observations shown in section 4 and at the same time are consistent with observed values reported in Heymsfield and Kajikawa [1987].…”

Section: Large-eddy Simulation Of the Cold Air Outbreak Casementioning

confidence: 54%

The “Grey Zone” cold air outbreak global model intercomparison: A cross evaluation using large‐eddy simulations

Tomassini

Field

Honnert

et al. 2017

J Adv Model Earth Syst

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A stratocumulus‐to‐cumulus transition as observed in a cold air outbreak over the North Atlantic Ocean is compared in global climate and numerical weather prediction models and a large‐eddy simulation model as part of the Working Group on Numerical Experimentation “Grey Zone” project. The focus of the project is to investigate to what degree current convection and boundary layer parameterizations behave in a scale‐adaptive manner in situations where the model resolution approaches the scale of convection. Global model simulations were performed at a wide range of resolutions, with convective parameterizations turned on and off. The models successfully simulate the transition between the observed boundary layer structures, from a well‐mixed stratocumulus to a deeper, partly decoupled cumulus boundary layer. There are indications that surface fluxes are generally underestimated. The amount of both cloud liquid water and cloud ice, and likely precipitation, are under‐predicted, suggesting deficiencies in the strength of vertical mixing in shear‐dominated boundary layers. But also regulation by precipitation and mixed‐phase cloud microphysical processes play an important role in the case. With convection parameterizations switched on, the profiles of atmospheric liquid water and cloud ice are essentially resolution‐insensitive. This, however, does not imply that convection parameterizations are scale‐aware. Even at the highest resolutions considered here, simulations with convective parameterizations do not converge toward the results of convection‐off experiments. Convection and boundary layer parameterizations strongly interact, suggesting the need for a unified treatment of convective and turbulent mixing when addressing scale‐adaptivity.

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An Improved Approach to Calculating Terminal Velocities of Plate-like Crystals and Graupel

Cited by 160 publications

References 0 publications

Observations of the Falling Motion of Plate-Like Snow Crystals Part I: The Free-Fall Patterns and Velocity

Observations of the Falling Motion of Plate-Like Snow Crystals Part I: The Free-Fall Patterns and Velocity

Doppler lidar measurements of oriented planar ice crystals falling from supercooled and glaciated layer clouds

The “Grey Zone” cold air outbreak global model intercomparison: A cross evaluation using large‐eddy simulations

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