Introduction

In this chapter, we consider lightning discharges initiated by leaders that originate from stationary grounded objects, usually tall towers, and propagate upward toward charged clouds overhead. Upward lightning, as opposed to “normal” downward lightning, would not occur if the object were not present and, hence, can be considered to be initiated by the object. As noted in subsection 2.9.1, objects with heights ranging from approximately 100 to 500 m experience both downward and upward flashes, the fraction of upward flashes increasing with the height of the object. The observed percentage of upward flashes for structures of different heights is given in Table 2.3. Structures having heights less than 100 m or so are usually assumed to be struck only by downward lightning, and structures with heights greater than 500 m or so are usually assumed to experience only upward flashes. In other words, upward flashes are usually neglected for structures lower than 100 m, and downward flashes are neglected for structures taller than 500 m. Apparently, all lightning discharges recorded by Davis and Standring (1947), who measured currents in the cables of kite balloons flying at a height of 600 m in England, were of the upward type.