Measurement and Interpretation of Hailstone Density and Terminal Velocity

Knight, Nancy C.

doi:10.1175/1520-0469(1983)040<1510:maiohd>2.0.co;2

Cited by 66 publications

(61 citation statements)

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“…The velocities of fast-falling pellets were very close to the raindrop terminal velocity (Atlas et al 1973). The velocities of slow-falling pellets were close to a terminal velocity of average-density (0.44 g cm 23 ) hailstones (Knight and Heymsfield 1983). In section 4b, reasons for classifying the two modes of fall velocity are discussed in detail from the viewpoint of ice pellet geometrical properties in 2DVD data and in comparison with previous studies on precipitation particle microphysics.…”

Section: Surface Observationssupporting

confidence: 65%

“…Most of the slow-falling particles were even slower than hailstones with densities of 0.91 g cm 23 and close to the fall velocity of averagedensity (0.44 g cm 23 ) hail (solid red line in Fig. 9) (Knight and Heymsfield 1983). These facts suggest that the slow-falling particles had very tiny rough surfaces, similar to those of dry hailstones.…”

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 66%

“…A very tiny (microscopic scale) rough surface can have a significant impact on the drag coefficient of small particles with a low Reynolds number (Selberg and Nicholls 1968;Rasmussen and Heymsfield 1987;Heymsfield and Wright 2014). Since dry hailstones with densities of 0.91 g cm 23 have tiny rough surfaces and high drag coefficients (Knight and Heymsfield 1983), their terminal fall velocities are significantly lower than those of smooth ice spheres (dotted blue and green lines in Fig. 9) (Knight and Heymsfield 1983;Thériault and Stewart 2010;Kumjian et al 2012).…”

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 98%

“…Relationship between fall velocity and diameter of IPs observed from 0900 to 1000 LST. The solid blue line indicates velocity-diameter relationships for raindrops (Atlas et al 1973), the solid green line indicates hailstones with a density of 0.91 g cm 23 , and the solid red line indicates the average density of hailstones (0.44 g cm 23 ) (Knight and Heymsfield 1983). The dashed blue line indicates terminal fall velocities for smooth ice spheres with densities of 0.91 g cm 23 , and the dashed red line indicates those for smooth ice spheres with densities of 0.16 g cm 23 (Mikhailov and Silva Freire 2013).…”

Section: ) Numerical Simulationsmentioning

confidence: 99%

“…Since dry hailstones with densities of 0.91 g cm 23 have tiny rough surfaces and high drag coefficients (Knight and Heymsfield 1983), their terminal fall velocities are significantly lower than those of smooth ice spheres (dotted blue and green lines in Fig. 9) (Knight and Heymsfield 1983;Thériault and Stewart 2010;Kumjian et al 2012). Most of the slow-falling particles were even slower than hailstones with densities of 0.91 g cm 23 and close to the fall velocity of averagedensity (0.44 g cm 23 ) hail (solid red line in Fig.…”

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 99%

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Microphysical Properties of Slow-Falling and Fast-Falling Ice Pellets Formed by Freezing Associated with Evaporative Cooling

Nagumo

Fujiyoshi

2015

Monthly Weather Review

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This paper describes a numerical and observational study focused on ice-pellet formation and microphysical properties near 08C from an ice-pellet-dominated storm associated with an unusually warm and dry atmosphere on 10 April 2005, in Sapporo, Japan. A one-dimensional numerical model simulation indicated that precipitation particle temperatures were sensitive to environmental temperature and relative humidity and close to the wet-bulb temperature. The simulation demonstrated that completely melted snowflakes could refreeze by evaporative cooling. Moreover, initial freezing could be explained by contact ice nucleation at the height of the minimum wet-bulb temperature.Observations using a 2D video distrometer (2DVD) indicated that ice pellets exhibited two modes of fall velocities at surface temperatures near 08C during the same time period: slow falling and fast falling. The slowfalling ice pellets exhibited a velocity similar to the average terminal velocity of hail, whereas the velocities of the fast-falling ice pellets were closer to those of raindrops. Surface roundness and fracturing characteristics of ice pellets suggest that slow-falling ice pellets froze rapidly and uniformly in a relatively cold dry layer with a wet-bulb temperature near 248C. In contrast, the fast-falling ice pellets exhibited the properties of ice particles with a wet smooth surface, suggesting that they froze slowly in a relatively warm layer by contacting ice crystals or splinters generated by preceding slow-falling ice pellets.

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Section: Surface Observationssupporting

confidence: 65%

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 66%

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 98%

Section: ) Numerical Simulationsmentioning

confidence: 99%

Section: ) Properties Of Ice Pellets Derived From Fall Velocitiesmentioning

confidence: 99%

See 3 more Smart Citations

Microphysical Properties of Slow-Falling and Fast-Falling Ice Pellets Formed by Freezing Associated with Evaporative Cooling

Nagumo

Fujiyoshi

2015

Monthly Weather Review

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The Perils in Brief

Hillier¹

2017

Natural Catastrophe Risk Management and Modelling

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A modeling study of ice formation affected by aerosols

Han

Yang

2013

JGR Atmospheres

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[1] This study investigates the effects of cloud condensation nuclei (CCN) and ice nuclei (IN) on ice formation in mixed-phase clouds using an adiabatic parcel model. The simulations with lower updrafts represent mixed-phase stratiform clouds, and those with higher updrafts represent deep convective clouds. Increasing CCN concentration can lead to more ice crystals with smaller sizes, but does not affect the height of freezing nucleation at lower updrafts. At higher updrafts, ice number concentration is more sensitive to CCN, and CCN effect on ice nucleation height is also more noticeable. This study also investigates the effects of IN properties (number concentration, size, contact angle) on ice formation assuming the immersion freezing mechanism. At very low IN number concentration, ice nucleation is dominated by homogeneous freezing and ice number concentration is relatively high. As IN number concentration is increased, ice number concentration decreases because both heterogeneous and homogeneous freezing processes occur. A mixed-phase layer extends up to the height for homogeneous freezing and there is a competition between the two freezing processes. As IN number concentration is further increased, ice number concentration increases because heterogeneous freezing dominates ice nucleation. IN number concentration needs to be higher for heterogeneous freezing to dominate ice nucleation at higher updrafts and lower at lower updrafts. Increasing IN size and contact coefficient also increases the contribution of heterogeneous freezing to ice nucleation. Finally, spheroids are used to represent columnar and plate-like ice crystals. CCN and IN effects are not dependent on the assumption of ice crystal shapes.

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Measurement and Interpretation of Hailstone Density and Terminal Velocity

Cited by 66 publications

References 0 publications

Microphysical Properties of Slow-Falling and Fast-Falling Ice Pellets Formed by Freezing Associated with Evaporative Cooling

Microphysical Properties of Slow-Falling and Fast-Falling Ice Pellets Formed by Freezing Associated with Evaporative Cooling

The Perils in Brief

A modeling study of ice formation affected by aerosols

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