Lightning Electromagnetic Fields Along an Ocean–Land Mixed Propagation Path Generated by Return Strokes to Wind Turbines

We evaluate lightning electromagnetic fields along an ocean-land mixed propagation path generated by return strokes to wind turbines (WTs) using a three-dimensional finite-difference time domain method. In these simulations, we consider the following three cases: strikes to onshore WTs, strikes to offshore floating WTs, and strikes to onshore WTs in the presence of horizontally stratified ground. Also, we investigate the effect on lightning electromagnetic fields of the following two parameters: distance d between the WT and the observation point, and distance dl between the coastline and the observation point. Generally, the lightning electromagnetic fields are affected by the ocean-land interface, and d and dl play an important role in the effect degree. For onshore WTs, the effect of a mixed path is visible on magnetic field and vertical electric field for d less than 300 m and horizontal electric field for d exceeding 300 m. The effect for dl = 10 m is stronger than that for dl = 50 m. For offshore WTs, the effect of a mixed path is significant and the effect for dl = 10 m is almost the same as that for dl = 50 m.