Abstract
Laboratory experiments were carried out inside the cylindrical steel chamber kept inside the walk-in cold room, which can reach a temperature of -30 degrees C, to investigate the effect of ionic compounds on charge transfer during the collision between ice crystals and graupel in the presence of supercooled water droplets. Experiments were carried out at a constant impact velocity of 2.2 m/s using pure water (Milli-Q, 18.2 M Omega-cm) and trace amount of ionic compounds at low rime accretion rate (RAR) and crystal sizes below 50 pm diameter in the temperature regions of -6 to -10 degrees C, -16 to -19 degrees C and -21 to -25 degrees C. It was observed that ice crystals interacting with graupel made of pure water obeys the charge sign regimes [Saunders, C.P.R., Keith, W.D., and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96, D6, 11007-11017.] as a function of temperature and RAR for all temperatures ranging from -6 to -25 degrees C. The validity of the positive and negative charging zones of Saunders et al. [Saunders, C.P.P Keith, W.D., and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96, D6, 11007-11017.] for low effective liquid water content (EW) was verified. (C) 2008 Elsevier B.V. All rights reserved.