ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-1661-2010 Measurements of electric charge separated during the formation of rime by the accretion of supercooled droplets Lighezzolo R. A. 1 Pereyra R. G. 1 Avila E. E. 1 FaMAF, Universidad Nacional de Córdoba, IFEG-CONICET, Córdoba, Argentina 15 02 2010 10 4 1661 1669 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/1661/2010/acp-10-1661-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/1661/2010/acp-10-1661-2010.pdf

In these experiments, the electric charge carried by single particles ejected from the surface of a graupel particle growing by riming was measured. Simulated graupel pellets were grown by accretion of supercooled water drops, at temperatures ranging from &minus;2 to &minus;10 &deg;C in a wind tunnel at air velocities between 5 and 10 m s<sup>&minus;1</sup>, with the goal of studying the charging of graupel pellets under conditions of secondary ice crystal production (Hallett-Mossop mechanism). The graupel, and induction rings upstream and downstream of the graupel, were connected to electrometers and analyzing circuits of sufficient sensitivity and speed to measure, correlate and display individual charging events. The results suggest that fewer than 1% of the ejected particles carry a measurable electric charge (>2 fC). Further, it was observed that the graupel pellets acquire a positive charge and the average charge of a single splinter ejected is &minus;14 fC. This mechanism of ejection of charged particles seems adequate to account for a positive charge of around 1 pC that individual precipitation particles of <i>mm</i>-size could acquire in the lower part of the cloud, which in turn could contribute to the lower positive charge region of thunderstorms.

 References Avila, E. E., Aguirre Varela, G. G., and Caranti, G. M.: Temperature dependence of static charging in ice growing by riming, J. Atmos. Sci., 52, 4515–4522, 1995. Avila, E. E., Aguirre Varela, G. G., and Caranti, G. M.: Charging in ice-ice collisions as a function of the ambient temperature and the larger particle average temperature, J. Geophys. Res., 101, 29609–29614. 1996. Avila, E. E., Caranti, G. M., Castellano, N. E., and Saunders, C. P. R.: Laboratory studies of the influence of cloud droplet size on charge transfer during crystal-graupel collisions, J. Geophys. Res., 103, 8985–8996, 1998. Avila, E. E., Castellano, N. E., and Saunders, C. P. R.: Effect of cloud droplet spectra on the average surface temperature of ice accreted on fixed cylindrical collectors, Q. J. R. Meteorol. Soc., 125, 1059–1074, 1999. Avila, E. E. and Pereyra, R. G.: Charge transfer during crystal graupel collisions for two different cloud droplet size distributions, Geophys. Res. Lett., 27, 3837–3840, 2000. Avila, E. E., Longo, G. S., and Bürgesser, R. E.: Mechanism for electric charge separation by ejection of charged particles from an ice particle growing by riming, Atmos. Res. 69 99–108, 2003. Bader, M., Gloster, J., Brownscombe, J. L., and Goldsmith, P.: The production of sub-micron ice fragments by water droplets freezing in free fall or on accretion upon an ice surface, Q. J. Roy. Meteorol. Soc., 100, 420–426, 1974. Bateman, M. G., Marshall, T. M., Stolzenburg, M., and Rust, W. D.: Precipitation charge and size measurements inside a New Mexico mountain thunderstorm, J. Geophys. Res., 104, 9643–9653, 1999. Bürgesser, R. E., Pereyra, R. G., and Avila, E. E.: Charge separation in updraft of convective regions of thunderstorm, Geophys. Res. Lett., 33, L03808, doi:10.1029/2005GL023993, 2006. Castellano, N. E, Avila, E. E., Saunders, C. P. R.: Dependence of the average surface temperature on cloud droplet spectra for rime ice accreted on fixed spherical collectors, J. Geophys. Res. 104, 23399–27406, 1999. Choularton, T. W., Latham, J., and Mason, B. J.: A possible mechanism of ice splinter production during riming, Nature, 274, 791–792, 1978. Choularton, T. W., Griggs, D. J., Humood, B. Y., and Latham, J.: Laboratory studies of riming and its relation to ice splinter production, Q. J. Roy. Meteorol. Soc. 106, 367–373, 1980. Dong, Y. Y. and Hallett, J.: Droplet accretion during rime growth and the formation of secondary ice crystals, Q. J. Roy. Meteorol. Soc., 115, 127–142, 1989. Foster, T. and Hallett, J.: A laboratory investigation of the influence of liquid water content on the temperature dependence of secondary ice crystal production during soft hail growth, Am. Met. Soc. Cloud Physics Conference, Chicago, 123–126, 1982. Griggs, D. J. and Choularton, T. W.: Freezing modes of riming droplets with application to ice splinter production, Q. J. Roy. Meteorol. Soc. 109, 243–253, 1983. Harris-Hobbs, R. L. and Cooper, W. A.: Field evidence supporting quantitative predictions of secondary ice production rates, J. Atmos. Sci., 44, 1071–1082, 1987. Hallett, J. and Mossop, S. C.: The production of secondary ice particles during the riming process, Nature, 249, 26–28, 1974. Hallett, J., Sax, R. I., Lamb, D., Ramachandra Murty, A. S.: Aircraft measurements of ice in Florida cumuli, Q. J. Roy. Meteorol. Soc. 104, 631–651, 1978. Hallett, J. and Saunders, C. P. R.: Charge separation associated with secondary ice crystal production, J. Atmos. Sci. 36, 2230–2235, 1979. Latham, J. and Mason, B. J.: Generation of electric charge associated with the formation of soft hail in thunderclouds, Proc. R. Soc., A 260, 537–549, 1961. Latham, J. and Stow, C. D.: The distribution of charge within ice specimens subjected to linear and non-linear temperature gradients, Q. J. Roy. Meteorol. Soc., 93, 121–125, 1967. Macklin, W. C. and Payne G. S.: A theoretical investigations of the ice accretion process, Q. J. R. Meteorol. Soc., 93, 195–214, doi:10.1002/qj.49709339606, 1967. Mason, B. J.: The rapid glaciation of slightly supercooled cumulus clouds. Q. J. Roy. Meteorol. Soc. 122, 357–365, 1996. Mo, Q., Detwiler, A. G., Helsdon, J. H., Winn, W. P., Aulich, G., and Murray, W. C.: Hydrometeor charges observed below an electrified cloud using a new instrument, J. Geophys. Res., 112, D13207, doi:10.1029/2006JD007809, 2007. Mossop, S. C. and Hallett, J.: Ice crystal concentration in cumulus clouds: Influence of the drop spectrum, Science 186, 632–633, 1974. Mossop, S. C.: Production of secondary ice particles during the growth of graupel by riming, Q. J. Roy. Meteorol. Soc. 102, 45–57, 1976. Mossop, S. C.: The influence of drop size distribution on the production of secondary ice particles during graupel growth, Q. J. Roy. Meteorol. Soc. 104, 323-330, 1978. Nag, A. and Rakov, V. A.: Some inferences on the role of lower positive charge region in facilitating different types of lightning, Geophys. Res. Lett., 36, L05815, doi:10.1029/2008GL036783, 2009. Pereyra, R. G., Avila, E. E., Castellano, N. E., and Saunders, C. P. R.: A laboratory study of graupel charging, J. Geophys. Res. 105, 20803–20813, 2000. Pereyra, R. G. and Avila, E. E.: Charge transfer measurements during single ice crystal collisions with a target growing by riming. J. Geophys. Res., 107(D23), 4735, doi:10.1029/2001JD001279, 2002. Pereyra, R. G., Bürgesser, R. E. and Avila, E. E.: Charge separation in thunderstorm conditions, J. Geophys. Res., 113, D17203, doi:10.1029/2007JD009720, 2008. Rayleigh, L.: On the equilibrium of liquid conducting masses charged with electricity, Phil. Mag. 14, 184–186, 1882. Saunders, C. P. R., Keith, W. D., and Mitzeva, R. P.: The effect of liquid water on thunderstorm charging, J. Geophys. Res. 96, 11007–11017, 1991. Saunders, C.P.R.: Thunderstorm electrification laboratory experiments and charging mechanisms. J. Geophys. Res., 99, D5, doi:10.1029/93JD01624, 1994. Saunders, C. P. R., Avila, E. E., Peck, S. L., Castellano, N. E., and Aguirre Varela, G. G.: A laboratory study of the effects of rime ice accretion and heating on charge transfer during ice crystalrgraupel collisions, Atmos. Res. 51, 99–117, 1999. Saunders, C. P. R., Peck, S. L., Aguirre Varela, G. G., Avila, E. E., and Castellano, N. E.: A laboratory study of the influence of the water vapour and mixing on the charge transfer process during collisions between ice crystals and graupel, Atmos. Res., 58, 187–203, 2001. Saunders, C. P. R. and Hosseini, A. S.: A laboratory study of the effect of velocity on Hallett-Mossop ice crystal multiplication, Atmos. Res., 59–60, 3–14, 2001. Saunders, C. P. R., Bax-Norman, H., Avila, E. E., and Castellano, N. E.: A laboratory study of the influence of ice crystal growth conditions on subsequent charge transfer in thunderstorm electrification, Q. J. Roy. Meteorol. Soc., 130/B, 1395–1406, 2004. Saunders, C. P. R., Bax-Norman, H., Emersic, C., Avila, E. E. and Castellano, N. E.: Laboratory studies of the effect of cloud conditions on graupel/crystal charge transfer in thunderstorm electrification, Q. J. Roy. Meteorol. Soc., 132/B, 2655–2676, 2006. Saunders, C. P. R.: Charge separation mechanisms in clouds, Space Sci. Rev., 137, 335?353, 2008. Takahashi, T.: Riming electrification as a charge generation mechanism in thunderstorms, J. Atmos. Sci. 35, 1536–1548, 1978. Williams, E. R.: The tripole structure of thunderstorms, J. Geophys. Res., 94, 13151–13167, 1989.