Calculation of triggered lightning current and electromagnetic fields based on spectral diagnosis and finite-difference time-domain method

The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, are analyzed using slit-free spectroscopy technology. Based on spectral diagnostic methods, the maximum and minimum values of the triggered lightning channel current are determined to be about 30.9 kA and 25.6 kA (minimum), respectively, and the current is simulated using a modified transmission line model with linear current decay (MTLL). To investigate the electric field distribution, the finite-difference time-domain (FDTD) method and transmission line (TL) model are employed. At a distance of 58 m, assuming a return stroke velocity of 1.3 × 10<sup>8</sup> m/s, the TL-predicted radiation electric field deviates from experimental electric field, but is very close to the FDTD-simulation of the vertical electric field. Moreover, the analyses of magnetic fields at 58 m, 90 m, and 1.6 km are compared using FDTD simulations, dipole approximation, and charge magnetic field limit (CMFL) estimation. The discrepancies between calculated value and experimental values appear at 58 m and 90 m, which may be due to the near-field interference and measurement limitation. However, they become small at 1.6 km. This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.