Mechanism for electric charge separation by ejection of charged particles from an ice particle growing by riming

Experimental evidence is presented that shows that substantial electric charge separation can occur by the ejection of charged particles during the riming process. Measurements were performed at temperatures between −15 and −30 °C, velocities between 10 and 30 m s−1 and cloud water contents between 0.2 and 1 g m−3. Results show that positively or negatively charged particles were detached from an artificial hailstone, with individual charges ranging between −0.3 and 0.5 pC. This mechanism could separate approximately 5 pC min−1 cm−2 of hail surface area. The charge of the ejected particle depends on the environmental temperature. Charge separation was detected at air velocities above 17 m s−1, which indicates that the mechanism could operate in the presence of hailstones larger than 1 cm in diameter. This mechanism is distinct from the usual noninductive mechanism and does not require ice particle collisions to separate electric charge. The physical mechanism has not been elucidated yet, but the results suggest that the ejected particles could be produced by splashing of droplets impinging on the artificial hailstone or by detachment of rime fragments accreted on it.