Polarization Charging Effect and Thundercloud Electrification

WE have found, using solid state electrometers capable of measuring individual charges during ice–ice collisions, that polarization charging may be an effective charge generating mechanism in glaciated or partly glaciated clouds1–4. The high sensitivity of the electrometers made it possible to measure charges as low as 10−6 e.s.u. with millisecond transfer times. It seems that nearly all snow crystals carry a charge of this order or greater, and collisions of these crystals with an ice sphere produces an average charge of about 5 × 10−5 e.s.u. when no potential gradient is present. When a potential gradient of 50 V cm−1 is present, however, an average charge of 2 × 10−3 e.s.u. is produced during a single collision. This supports our proposed mechanism.