The Influence of Diffusional Growth Rates On the Charge Transfer Accompanying Rebounding Collisions Between Ice Crystals and Soft Hailstones

Abstract

Laboratory experiments designed to investigate the charge transfer accompanying rebounding collisions between ice crystals and soft hailstones were performed inside a cold room. They constitute an extension of those conducted with the same apparatus, reported in 1983 by Jayaratne et al. In particular, the range of temperature was extended (to cover -1.5"C to -35°C) and specific tests were performed in an effort to establish relationships between the sign and magnitude of the charging and the growth characteristics of both types of hydrometeor.Significant charging was obtained only when the interacting surfaces were growing by vapour diffusion. The sign of the current, I , flowing to the simulated soft hailstone target in these circumstances was a sensitive function of time, liquid water content, and temperature. The complete set of results is qualitatively consistent with the hypothesis that I is positive if the target surface is growing more rapidly from the vapour than the ice crystals and is negative for the opposite case. In formulating a qualitative model of this hypothesis, account is taken of the contribution made to the diffusional growth of the target by the flux of vapour from droplets freezing onto its surface.Crude calculations designed to assess the implications of these studies with respect to thunderstorm electrification, yield the conclusion that negative soft hailstone charging is likely to predominate over positive in most circumstances.Production of laboratory clouds. ibid., 110, 275-279 Meteorological applications of lightning data. Rev. Geophys., Microphysics of clouds and precipitation. D. Reidel. Pub. Co. A numerical study of thunderstorm electrification using a three-dimensional model incorporating the ice phase. Q.

Using a cloud electrification model to study relationships between lightning activity and cloud microphysical structure

“…The electrification and, hence, lightning is associated with the region of particle interactions. The high altitude of supercooled droplets (panel III) is a testament to the vigorous updraft, which strongly influences the graupel production/particle interactions in the CZ, identified as the region where the noninductive electrification processes occur (Takahashi, 1978;Jayaratne et al, 1983;Baker et al, 1987).…”

“…In this study an electrification scheme based on the noninductive ice-ice process is used (Reynolds et al, 1957;Saunders et al, 1991;Jayaratne et al, 1983;Mason and Dash, 2000;Nelson and Baker, 2003), in which the sensitivity of the charge transfer mechanism to particle size can be adequately represented (Saunders et al, 1991;Solomon et al, 2005;Mansell et al, 2010). Several parameterizations of the noninductive ice-ice process exist (e.g., Takahashi, 1978;Gardiner et al, 1985;Brooks et al, 1997;Saunders and Peck, 1998), and several studies have shown that storm electrification (i.e., cloud polarity and the lightning characteristics) is highly sensitive to this parameterization (e.g., Mansell et al, 2005;Kuhlman et al, 2006;Barthe and Pinty, 2007). Takahashi (1978) and Saunders et al (1991) have shown that magnitude and sign of the charge transferred to each colliding particle are strong functions of liquid water content and temperature.…”

“…In the EMTM, based on observational evidence and model results by several authors (Gardiner et al, 1985;Dye et al, 1989;Norville et al, 1991), it is assumed that the dominant charge transfer mechanism involves collisions between ice crystals and graupel particles or soft hail pellets -see also Takahashi (1978), Jayaratne et al (1983), Baker et al (1987), and Saunders et al (1991). This mechanism requires the coexistence of ice, graupel, and supercooled liquid water in the so-called charging zone (CZ) -defined here according to Saunders (2008) as the vertical layer between 0 • C and −25 • C. When ice crystals and graupel particles collide, the charged graupel are either suspended within the CZ or sediment downward depending on their fall velocity as compared to the updraft velocity in the CZ, while the ice crystals, charged by the opposite sign with respect to graupel, are carried upward in the cloud.…”

Effects of environmental conditions on inducing charge structures of thunderstorms over Eastern India

“…Small inverted polarity thunderstorms reported by Gopalakrishnan et al (2010) in this region and by Pawar and Kamra (2002, and 2009) at Pune, India, support the idea that large ice nuclei concentrations can play an important role in the alteration of charge structures of thunderstorms with moderate or low instability. Many laboratory experiments (Baker et al 1987; Williams Caranti et al 1991) suggest that dominant positive charge will appear on larger precipitation particles in the lower portion of the mixed-phase region if ice saturation is maintained. The authors are aware that the aerosol and/or ice nuclei concentrations cannot influence the polarity of thunderstorms by themselves.…”

Evaluation of Lightning Forecasting Based on One Lightning Parameterization Scheme and Two Diagnostic Methods

“…Latham and Mason [4] found that the sign of the charging which results from collisions between ice crystals and a simulated hailstones is governed by that of the temperature difference, and it is rather insensitive to the size and impact velocity of the crystals. The controllable factor of charge transfer was found by Baker et al [5]. Significant charging was obtained only when the interacting surfaces were growing due to vapor diffusion.…”