Reproduction of Electromagnetic Field Waveforms of Downward Lightning Strokes Hitting Tokyo Skytree

Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower. Electromagnetic field waveforms have been also observed by calibrated capacitive antennas at several tens of kilometers from the tower. Simultaneously observed lightning current and electric field waveforms are reproduced by using an electromagnetic model of a return stroke over lossy ground with the help of NEC-4. Lightning channel models with inclination are reconstructed from observed images. Consequently, it turns out that the electromagnetic field waveforms are affected by the geometrical shape of a lightning channel, current refractions in the tower, ground conductivity, and current wave velocity in the lightning channel. NEC-4 is quite useful for such analysis of lightning strokes hitting high structures.