Lightning Current Waveforms Inferred From Far-Field Waveforms for the Case of Strikes to Tall Objects

Electric and magnetic fields at far distances produced by lightning strikes to tall objects are different from those associated with lightning strikes to flat ground. Specifically, in the case of strikes to tall objects, the waveforms are oscillatory because of current reflections at the top and bottom of the tall object. In this article, a procedure to reconstruct the waveform of far electric field due to the lightning strike to flat ground from the corresponding waveform of far electric field due to a lightning strike to a tall object is proposed. Once the effect of tall strike object is removed from the measured field waveform, the channel-base current for the strike to flat ground is estimated. Further, the channel-base current waveform is used to find the waveform of current at any altitude along both the strike object and the lightning channel. Computations of far electric fields due to lightning strikes to tall objects are carried out using the finite-difference time-domain method in the two-dimensional cylindrical coordinate system. The lightning return stroke is represented by the transmission-line (TL) model, the modified TL model with linear current decay with height, or the modified TL model with exponential current decay with height.