The influence of impact velocity and ice specimen geometry on the charge transfer associated with temperature gradients in ice

Abstract

AbstractWhen pure uniform ice specimens of different temperatures are brought into gentle contact for times ranging from 10−3 to 5.10−2 sec and are then separated, the charge transfer is a maximum for a contact time of about 7.5 × 10−3 sec and is in agreement with the equations of Latham and Mason (1961a). With ice of higher conductivity the maximum charge transfer occurs after smaller contact times.For impact velocities less than about 7.5 cm sec−1 the charge transfer is in agreement with the theory but above this value the charge transfer increases linearly with impact velocity. The charge transfer is also enhanced, by as much as an order of magnitude, if the ice specimens are tapered. A tentative conclusion to be drawn from these experiments is that the value of 5 × 10−4 e.s.u., measured by Reynolds, Brook and Gourley (1957) for the charge transfer per collision between an ice crystal and a warmer artificial hailstone, which is sufficient to generate charge at a rate required by a tenable theory of thunderstorm electrification, may be explicable in terms of the temperature‐gradient effect.When steady temperature gradients are applied to uniform specimens of pure ice the potentials developed across the ice are unaffected by the pressure to which the ice is subjected. The application of steady temperature gradients to tapered ice specimens produces potentials which are up to an order of magnitude greater than predicted theoretically.