Influence of channel tortuosity on the lightning return stroke electromagnetic field in the time domain

The effect of lightning channel tortuosity on the associated electromagnetic (EM) fields in the time domain is investigated quantitatively from a new point of view. Due to the vanishing of geometric symmetry when taking into account the tortuosity of lightning channels, it is necessary to calculate the associated EM fields in the Cartesian coordinate system. An efficient technique is adopted to produce tortuous lightning channels and then the fractal dimension of the channel is calculated automatically by a program. The results show that at close distances, the dependence of EM fields on azimuth is significant, the ratio of MF peaks at two coaxial points with the channel base may reach about 4 and that of the EF may be larger than 2. With increased distance, the dependence of waveform on azimuth weakens. At distances of 10 km and 100 km, the current peaks derived from the EF peaks show good consistency with the current peak adopted, with an uncertainty less than 25%.