The freezing of raindrops falling through strong electric fields

Supercooled water drops of radius around 2 mm and temperature ranging from 0 to −12°C were detached from a support and could be disrupted as they subsequently fell into a region of intense electric field. Photographs showed that whereas no freezing occurred if the drops were not disrupted the fraction of drops that froze increased steadily from 0 at about −5°C to around 0.6 at –10°C if they were disrupted. The passage of a spark to the drops during disruption did not affect the freezing probability. Studies were made on about 200 drops. A series of experiments on bulk supercooled water and drops suspended from mechanical supports indicated that nucleation was initiated by means of cavitation. This conclusion was reinforced by high speed photographs showing the production and collapse of cavity bubbles when disruption occurred and indicating strongly that freezing initiated from the sites of these bubbles at the time of their collapse.