Computations of Electromagnetic Fields Radiated From Complex Lightning Channels

In this paper, three methods for calculating electromag- netic fields radiated from complex lightning channels are discussed, which includes channel obliqueness, branches and tortuosity. By ro- tating and moving the coordinate system of the vertical channel, differ- ential expressions of electromagnetic fields from the irregular channel can be derived from the conclusions of the straight and vertical chan- nel. Through analyzing calculation results of two examples reveals that channel tortuosity and branch is to introduce the higher frequency con- tent above 100 kHz into lightning electromagnetic fields.