The spectra of charging events due to the collision of natural ice particles with an ice surface

Scott, William

doi:10.1002/qj.49709440207

Cited by 12 publications

(3 citation statements)

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“…The force of the collision between the particles and roughness of the ice surfaces are also factors. Scott and Hobbs (1968) showed that the sign of the charge acquired by an ice specimen from a collision depends on the shapes of the particles involved and the magnitude of the charge acquired increases with increased impact velocities. Latham and Stow (1965) found that charge transfer associated with the thermoelectric effect could be greatly enhanced if the ice specimens are rough and if impact velocities are high.…”

Section: Electrification In Blizzardsmentioning

confidence: 99%

A theoretical prediction of the effects of electrostatic forces on saltating snow particles

Schmidt

Dent

1993

A. Glaciology.

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ABSTRACT. Electrification of snow particles during blizzards creates forces that may strongly effect their trajectories in saltation along a charged surface. This paper shows the results of adding such forces to the equations of motion for saltation. Evaluating these equations requires knowledge of the electric-field strength very near the surface, and a review shows that such measurements are lacking. However, extrapolation of reported measurements from greater heights agrees with the electric field computed for a bed of spherical particles. In this hypothetical field, the equations of motion predict large changes in saltation length that might occur as particles pass over surfaces with positive and negative sign. Such changes apparently coincide with surface erosion and deposition.

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Section: Electrification In Blizzardsmentioning

confidence: 99%

A theoretical prediction of the effects of electrostatic forces on saltating snow particles

Schmidt

Dent

1993

A. Glaciology.

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“…Collision or riming give rise to these processes [Latham and Mason, 1961b;Scott and Hobbs, 1968;Hallett and Saunders, 1979]. The charge carried off by ejected splinters or secondary crystals may have been generated at the newly created surface, or it may have been present before splintering in the form of surface electrons, induced charge, or as the result of thermal or concentration gradients.…”

Section: Splintering and Secondary Crystal Productionmentioning

confidence: 99%

“…Superposed on the three previous mechanisms are the charge separation effects due to splintering, or secondary crystal production, and to inductive polarization by an external field. Depending on strength and sign of the latter, separation of inductively polarized charge by colliding particles may enhance or reduce charge separation by other processes [e.g., Buser, 1976]; it may become dominant [Shewchuk and Iribarne, 1974] and then determine the sign of overall charge separation [Hobbs and Burrows, 1966;Burrows et al, 1967;Scott and Hobbs, 1968;Pruppacher and Klett, 1978, pp. 601-605].…”

Section: Collision Mechanisms In Perspectivementioning

confidence: 99%

Role of relaxation and contact times in charge separation during collision of precipitation particles with ice targets

Gross¹

1982

J. Geophys. Res.

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The relaxation time of charge transfer and the contact time are two of the parameters controlling charge separation when ice particles collide with one another or with liquid water droplets. For maximum efficiency of charge separation, the relaxation time should be of the same order as the contact time. The relaxation time of charge transport in ice was systematically determined as a function of impurity content and temperature. The contact time for ice/ice collisions was estimated from theory. Depending on the impurity species and their concentration, the relaxation time may be increased or decreased by orders of magnitude with respect to pure ice. Only particles of the order of 10−2 m radius seem to have contact times sufficiently long to give appreciable charge separation by ion transport in collisions between pure or slightly doped (0.1 ppm chloride) ice particles in a dry environment. Charge separation mechanisms involving liquid water and those operating by the transfer of electrons from surface states largely relax these conditions. These results have implications for cloud electrification models involving collision mechanisms.

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The charging of ice surfaces by natural ice particles

Stow

1969

Quart J Royal Meteoro Soc

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I am concerned about a recent paper by W. D. Scott and P. V. Hobbs, ' The spectra of charging events due to the collision of natural ice particles with an ice surface ' (Quart. 1, R. Met. Soc., 94,. A number of points seem to me to deserve clarification or comment and I shall discuss them in the order that they appear in the paper.Scott and Hobbs state in their introduction that an ice sphere moving through natural snowfall acquired a charge the sign of which was dependent on the direction of the vertical electric field. They infer that therefore the majority of the charge acquired by the sphere was due to the direct transfer of some of the charge already on the ice particles. This statement is somewhat misleading since an identical relationship between charging and electric field could exist even if the snow crystals initially carried no net charge. Charging in such an instance is the result of the transfer of polarization charges during momentary contact; the theory of this mechanism has been developed by Muller-Hillebrand (1954, 1955.The design of the electrometer calls for some comment. Scott and Hobbs rightly extol the virtues of the field-effect transistor in this application, though electrometer valves with guardring degeneration of input capacitance have been capable of comparable performances for some years. Scott and Hobbs do not indicate how the sensitivity (as distinct from input capacitance) of their electrometer was verified during field operations; as no mention is made of a stabilized power supply such a check would appear to be an essential part of the measurement technique. In addition, I have found that sheathing of the amplifier components in highly polarizable materials such as polyethylene and teflon can cause spurious output signals, not unlike the signals measured here, if the amplifier is mechanically vibrated. An operational amplifier with an integral FET input stage would be a much more stable system than the one used by Scott and Hobbs.In the treatment of their results Scott and Hobbs point out correctly that the effect of the roughness of the ice surface, the impact velocity, and the degree of fragmentation of the natural ice particles are extremely important factors in the charging process, especially with regard to the temperature-gradient mechanism. It is difficult to understand why they have not made even an order-of-magnitude calculation of the efficacy of such a mechanism. For example, Latham and Mason (1961) have shown that the charge transferred between ice specimens of different temperature (T, and T2) during momentary contact has a maximum value of where A is the actual area of contact, and the contact time for maximum charge transfer is of the order s.Inserting the median value of 2 x e.s.u. per collision obtained by Scott and Hobbs (T, -T2) A 2: 6.7 x "C cm2.Although, unfortunately, no data are given the superficial area of contact between an ice crystal and the ice surface Scott and Hobbs used would probably be of the order cm2, and the real area of contact much less,...

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The spectra of charging events due to the collision of natural ice particles with an ice surface

Cited by 12 publications

References 11 publications

A theoretical prediction of the effects of electrostatic forces on saltating snow particles

A theoretical prediction of the effects of electrostatic forces on saltating snow particles

Role of relaxation and contact times in charge separation during collision of precipitation particles with ice targets

The charging of ice surfaces by natural ice particles

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