Lightning-counter measurements in Scandinavia

Abstract
The number of days with perceptible thunder in a year (isoceraunic level or i.c.l.) has generally been used as a measure for the effects of lightning on transmission lines. However, the i.c.l. is a very vague measure, and a far better method is to count the daily number of lightning strokes to earth using some counting device.The paper describes lightning-counter measurements in Norway, Sweden and Finland during 1963 and some earlier years. The Pierce-Golde counter of English design has been used, although it was found advisable to reduce the sensitivity of the counter to half of the original value. This reduced sensitivity has now been adopted universally.The number of lightning strokes per thunderstorm day has varied greatly, and the number of lightning strokes per summer seems to be proportional to the square of the i.c.l. rather than to the i.c.l. itself. Thus, the i.c.l. seems to be a rather inadequate measure for lightning effects. However, in order to obtain reliable statistical information, the lightning-counter measurements should be carried out for at least ten years and in as many parts of the world as possible.

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