HR: 11:05h
AN: AE51B-03    [PDF]
TI: Memory effect in the collisional charging of ice
AU: Dash, J
EM: dash@dirac.phys.washington.edu
AF: Department of Physics, University of Washington, Box 351560, Seattle, WA 98105 United States
AU: Mason, B L
EM: bmason@thinkSRS.com
AF: Stanford Research Systems, 1290 D Reamwood Ave., Sunnyvale, CA 94089 United States
AU: * Wettlaufer, J S
EM: john.wettlaufer@yale.edu
AF: Departments of Geology \& Geophysics and Physics, Yale University, Box 208109, New Haven, CT 06520 United States
AB: The theory of collisional charging of ice describes the formation of charge bilayers on ice due to rapid vapor growth[1]. OH- ions are bound at crystal edges and corners, and positive ions are distributed deeper in the ice. Charge transfer results from rebounding collisions which cause temporary melting of the surface, liberating the OH- ions into the liquid. On separation, the particles take approximately equal shares of the melt, thus the particle that had a greater density of negative surface ions loses more negative charge. The theory achieves quantitative agreement with experiment [3], with only one empirical constant, relating to the probability of ionization vs surface roughness. The theory explains the `polarity rule' developed from laboratory studies: The particle experiencing faster vapor growth becomes positively charged [2]. However, further analysis now leads us to elaborate the theory. Surface roughness is semipermanent as long as temperature stays well below melting [4], because annealing to smooth facets is a collective process, virtually impossible to achieve by the diffusion of independent single atoms. Therefore, rapid vapor growth accumulates disordered layers, building to a thickness proportional to the growth rate and the duration of the growth. This explains why, in a series of repetitive collisions, the charge transfer increased over a period of several minutes between events [4]. Consequently, we amend the polarity rule: In a rebounding collision, the particle which had experienced the greater time-integrated vapor growth rate becomes positively charged, if temperature has remained continuously colder than a few degrees below 0o C. A surface initially disordered will continue disordered growth during slow deposition, by virtue of epitaxy with the underlying roughness. [1] J.G. Dash, B.L. Mason and J.S. Wettlaufer, Theory of charge and mass transfer in ice-ice collisions, J. Geophys. Res. 106, 20395-20402 (2001); J.G. Dash and J.S. Wettlaufer, The surface physics of ice in thunderstorms, Can. J. Phys. 81, 201-207 (2003). [2] B. Baker, M.B Baker, E.R. Jayaratne, J. Latham and C.P.R. Saunders, The influence of diffusional growth rates on the charge transfer accompanying rebounding collisions between ice crystals and soft hailstones, Quart. J. Roy. Met. Soc. 113, 1193-215 (1987), and references therein. [3] B.L. Mason and J.G. Dash, Charge and mass transfer in ice-ice collisioms: experimental observations of a mechanism in thunderstorm electrification, J. Geophys. Res. 105,10185-10192 (2000). [4]. Reference 3, Fig.5.
DE: 3304 Atmospheric electricity
DE: 3314 Convective processes
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting