The collection efficiency of a cylindrical target for ice crystals

Keith, W. D.; Saunders, C. P. R.

doi:10.1016/0169-8095(89)90059-8

Cited by 26 publications

(9 citation statements)

References 8 publications

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“…We do not know what fraction of the crystals that collide with aggregates or other particles succeed in separating from the collision (or dislodge other parts of the larger particle) and in transferring charge. Keith and Saunders () used rods of 0.5‐ to 5‐mm diameter to examine the collision efficiency and probability of separation and bounce off of ice crystals of different sizes and speeds colliding with the rods. For plates >60 μm in size colliding at 3 m/s they found the collision efficiency to be ~1.…”

Section: Charge Transfer From Nonriming Ice‐ice Collisionsmentioning

confidence: 99%

Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida

Dye

Bansemer

2019

JGR Atmospheres

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Airborne observations in deep stratiform and anvil clouds showed extensive layers of 10‐ to 40‐kV/m electric fields colocated with highly stratified uniform radar reflectivity of 20 to 25 dBZ from 5‐ to 9‐km altitude. Size distributions with numerous small‐ and intermediate‐sized ice crystals (mostly aggregates) and large aggregates were observed in these regions. We infer that the uniform electric field, radar reflectivity, and broad particle size distributions were the result of mesoscale updrafts, confirmed by high‐resolution images of particles showing diffusional growth and no riming. No measurable supercooled liquid water was found in these regions from −10 to −45 °C. Calculated particle collision rates from observed distributions were >5 × 103 collisions per cubic meter per second in this volume. Laboratory results show that weak charge separation occurs when ice particles collide and separate even in the absence of supercooled water. We infer that charge separation occurred in the mesoscale updrafts via a noninductive mechanism in which ice particles growing by diffusion collide and transfer charge without supercooled water being present. These regions with strong, uniform fields, stratified radar reflectivity, and broad size distributions also occurred in anvils that barely reached the melting zone. Thus, we deduce that the nonriming collisional mechanism acts at middle to upper cloud levels and is not dependent upon electrification occurring near the melting zone. This mechanism should produce two oppositely charged layers of charge with the top layer residing on smaller particles often existing near the top of the cloud.

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Section: Charge Transfer From Nonriming Ice‐ice Collisionsmentioning

confidence: 99%

Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida

Dye

Bansemer

2019

JGR Atmospheres

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“…For interactions between snow or ice crystals and graupel in dry‐growth mode, E g , y = 0.01 exp (0.1 T C ), where T C is the temperature in °C. At small crystal diameters, the collision efficiency can become much smaller than unity [e.g., Keith and Saunders , 1989], but this effect is not yet incorporated into the model. Another potential source of error is the assumed very low sticking probability, which results in a high “event probability” (EP; the product ɛ coll ɛ sep , where ɛ sep = 1 − ɛ stk is the separation probability), whereas Jayaratne et al [1983] and Keith and Saunders [1989] determined EP values on the order of 0.2.…”

Section: Thunderstorm Simulation Modelmentioning

confidence: 99%

Charge structure and lightning sensitivity in a simulated multicell thunderstorm

et al. 2005

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[1] A three-dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory-based parameterizations of noninductive graupel-ice charge separation are compared. Inductive (i.e., electric field-dependent) charge separation is tested for rebounding graupel-droplet collisions. Each noninductive graupel-ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50 L À1 ). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud-to-ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel-droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50 L À1 .Citation: Mansell, E. R., D. R. MacGorman, C. L. Ziegler, and J. M. Straka (2005), Charge structure and lightning sensitivity in a simulated multicell thunderstorm,

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“…Several laboratory studies investigated the formation of ice crystal aggregates (Hosler and Hallgren, 1960;Hobbs, 1965;Keith and Saunders, 1989). An important parameter is the aggregation efficiency, E agg , describing the probability that a close encounter of two ice crystals results in an aggregation event.…”

Section: Particle-based Aggregation Algorithmmentioning

confidence: 99%

A large‐eddy model for cirrus clouds with explicit aerosol and ice microphysics and Lagrangian ice particle tracking

Sölch

Kärcher

2010

Quart J Royal Meteoro Soc

115

136

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We introduce a novel large-eddy model for cirrus clouds with explicit aerosol and ice microphysics, and validate its central components. A combined Eulerian/Lagrangian approach is used to simulate the formation and evolution of cirrus. While gas and size-resolved aerosol phases are treated over a fixed Eulerian grid similar to the dynamical and thermodynamical variables, the ice phase is treated by tracking a large number of simulation ice particles. The macroscopic properties of the ice phase are deduced from statistically analysing large samples of simulation ice particle properties. The new model system covers non-equilibrium growth of liquid supercooled aerosol particles, their homogeneous freezing, heterogeneous ice nucleation in the deposition or immersion mode, growth of ice crystals by deposition of water vapour, sublimation of ice crystals and their gravitational sedimentation, aggregation between ice crystals due to differential sedimentation, the effect of turbulent dispersion on ice particle trajectories, diabatic latent and radiative heating or cooling, and radiative heating or cooling of ice crystals. This suite of explicitly resolved physical processes enables the detailed simulation and analysis of the dynamical-microphysical-radiative feedbacks characteristic of cirrus.We draw special attention to the ice aggregation process which redistributes large ice crystals vertically and changes the ice particle size distributions accordingly. We find that aggregation of ice crystals is the key process to generate precipitation-sized ice crystals in stratiform cirrus. A process-oriented algorithm is developed for ice aggregation based on the trajectories and sedimentation velocities of simulation ice particles for use in the dynamically and microphysically complex, multi-dimensional large-eddy approach. By virtue of an idealized model set-up, designed to isolate the effect of aggregation on the cirrus development, we show that aggregation and its effect on the ice crystal size distribution in the model is consistent with a theoretical scaling relation, which was found to be in good agreement with in situ measurements.

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The collection efficiency of a cylindrical target for ice crystals

Cited by 26 publications

References 8 publications

Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida

Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida

Charge structure and lightning sensitivity in a simulated multicell thunderstorm

A large‐eddy model for cirrus clouds with explicit aerosol and ice microphysics and Lagrangian ice particle tracking

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