Charge separation in collisions between ice crystals and a spherical simulated graupel of centimeter size

Abstract

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 g m−3, for ambient temperatures between −5 and −30 °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 °C, and positively at temperatures above −15 °C.