Charge Separation in Collisions Between Ice Crystals and a Spherical Simulated Graupel of Centimeter Size

This work reports a new laboratory study of the electric charge separated in collisions between a spherical target of 1 cm in diameter growing by riming and vapor-grown ice crystals, with the objective of studying the charging behavior of the larger ice precipitation particles in thunderstorms in terms of the noninductive mechanism. A series of experiments was conducte d for a wide range of environmental conditions; the measurements were performed for effective liquid water content between 0.5 and 5 gm(-3), for ambient temperatures between -5 and -30 degrees C and at air speed of 11 m s(-1). The magnitude and sign of the electric charge transfer on the ice sphere as a function of the ambient temperature and the effective liquid water content is presented. The results show a charge reversal temperature for the riming target, which is roughly independent of liquid water concentration in the measured range. The simulated graupel charges negatively for temperatures below -15 degrees C, and positively at temperatures above -15 degrees C.