Propagation Characteristics of Lightning Radiation Field on Three-Layer Vertical Layered Ground Based on CPML Absorption Boundary

The perfectly matched layer absorbing boundary condition based on coordinate scaling transformation (CPML) has a good absorption effect in finite-difference time-domain method (FDTD) calculation. In this study, we derive the CPML update equations in the 2-D cylindrical coordinate system by setting an appropriate coordinate-stretching variable, which can more easily achieve CPML and obtain good results in the calculation of lightning electromagnetic field. Then, the propagation characteristics of the lightning return stroke radiation field on the three-layer vertical layered ground structure are studied. The results show the following: 1) at 10 m above the ground, the vertical electric field and azimuthal magnetic field are almost not affected by the vertically layered ground structure, while the horizontal electric field is slightly affected by the vertical layered ground structure and 2) at 3 m below the ground, the lightning radiation fields are all affected by the vertically layered ground structure, which the vertical electric field is the most affected, and it can also use two-layer vertical layered ground structure instead of three-layer vertical layered ground structure for FDTD calculation under certain conditions, which can simplify the calculation model. All the results are obtained at a close distance from the lighting channel.