Lightning Electric and Magnetic Fields Computation using the 3D-FDTD Method and Electromagnetic Models in Presence of Different Ground Configurations

Abstract

The three-dimensional finite difference time domain (3D-FDTD) method is employed to compute and to analyze the ground structure and conductivity effect on the lightning electromagnetic waveforms and their magnitudes. In this computation, the return-stroke current is represented by two electromagnetic models, namely: a vertical resistive wire having additional series distributed inductance and a vertical resistive wire coated by a fictitious material having a high relative permittivity and permeability. For validation needs, of the proposed calculating approach and the developed computation code, the obtained results are compared to those calculated by the achievement of analytical electromagnetic fields expressions taken from specialized literature. Against this comparison of these two approaches, a good agreement between results has been obtained validating thus our computation approach which has the advantage to take into account the real medium and ground geometry. At the end of this work we show that fields above a uniform or horizontally stratified ground near a vertical lightning return-stroke channel are not much influenced by the ground stratification, but the penetrating fields in the ground are influenced more by the presence of the stratified ground. It also appears that each electromagnetic model, tested in this work, yields reasonably accurate results of close electromagnetic fields.