Engineering Lightning Return Stroke Models Including an Elevated Strike Object: Far Field-Current Relationship

In this paper, we derive analytical expressions relating far-fields and currents associated with lightning strikes to tall towers. The derived equations are general and can be used with any engineering model. It is shown that the far field can be decomposed into three terms, namely (1) contribution of the main return stroke pulse, (2) contribution of the multiple-reflection process along the elevated strike object, including the contribution of pulses transmitted into the channel, and (3) contribution of the so-called ‘turn-on’ terms, associated with the current discontinuity at the return stroke wavefront. This discontinuity is associated with the extended tall tower-return stroke models. It is also shown that only the first term is model-dependent.