Lightning parameters of engineering interest

Abstract

Electrical discharges generated in the Earth's atmosphere by cumulonimbus clouds, volcanic eruptions, dust storms and snow storms are usually referred to as lightning discharges. In this chapter we confine ourselves to the lightning discharges produced by cumulonimbus clouds. Lightning discharges can be separated into two main categories, ground flashes and cloud flashes. Lightning discharges that make contact with ground are referred to as ground flashes and the rest are referred to as cloud flashes. Cloud flashes in turn can be divided into three types: intracloud flashes, air discharges and intercloud discharges. A ground flash can be divided into four categories based on the polarity of charge it brings to the ground and its point of initiation: downward negative ground flashes, downward positive ground flashes, upward positive ground flashes and upward negative ground flashes. The polarity of the flash, i.e. negative or positive, is based on the polarity of the charge brought to the ground from the cloud. Upward lightning flashes are usually initiated by tall objects of heights more than ~100 m or structures of moderate heights located on mountain and hill tops.