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Name: Jason
Status: student
Grade: N/A
Location: NH
Country: N/A
Date: 9/5/2005

Is lightning stroke DC current or AC current?

Lightning is DC -- well almost. There are several "kinds" of lightning. Cloud -- Earth = Cloud -- Earth -- Cloud; Cloud -- Cloud; Earth -- Cloud. In order of decreasing frequency. At least for most studies. Usually the charge carrier is negative (presumably electrons) but apparently some discharges appear to be positive! Often there is a "leader" stroke that on high speed photos approach the surface of the Earth, but "do not quite make it" and then there is a Earth -- Cloud return stroke (presumably the path is "set up" by the leader stroke. So this would be AC but with a single cycle. Make no mistake lightning is a difficult and complex phenomenon to study. It happens fast, and is difficult to track. Some studies "listen" to the thunder clap, which also provides interesting information, if not always well understood. The book "The Lightning Discharge" by Martin A. Uman is devoted to the subject. Interesting reading, thoroughly referenced. But after reading it there are more interesting questions than definitive answers.

Vince Calder

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