Temperature Dependence of Static Charging in Ice Growing by Riming

Abstract

Charge transfer between colliding ice particles is measured using a wind tunnel inside a cold room. A cylinder growing by riming in a wind tunnel was used as a target for collisions between 5 and 6 m s?1 with ice spheres of 100-µm diameter. The target temperature was adjusted to simulate different liquid water concentrations. As the target temperature increased, for air temperatures below ?18°C, initial positive target charging reversed sign to negative; with a further temperature increase the charging reversed sign again. These measurements, which are relevant to thunderstorm electrification, were carried out with and without riming and results are compared with other works. A novel approach is presented here suggesting a new pair of variables describing the charging.