Lightning and tall structures

摘要: The mechanism by which lightning is attracted to an earthed structure of low height well established, and the distances over strokes different intensities are (the so-called striking distances) have been determined. It appears that numerical values so established do not apply structures exceeding, say, 20m in height. In electric field under a thundercloud, tall produce point-discharge currents. Field observations shown resulting space charges can assume same shape as visible plume smoke from chimney. When normal negative leader approaches such positively charged `plume?, it will be it, unusually long `striking distances? result. A positive charge may broken up action violent updrafts downdrafts active thundercloud. pockets atmosphere held responsible for branching earth flashes. They also strikes points below tips standing on open ground. On other hand, suggested surrounded or trees subject roughly structures. furthermore present knowledge inadequate determine less frequent discharges.