An FDTD model for low and high altitude lightning-generated EM fields

To explore lightning-generated electromagnetic wave behavior and lightning-related ionospheric phenomena, a full-wave two-dimensional cylindrical finite-difference time-domain (FDTD) model was developed to simulate lightning-generated electromagnetic wave propagation in the ionosphere with high altitude and long distance capabilities. This FDTD model removes the approximations made in other,similar models to extend its applicability, and incorporates a variety of existing methods and new techniques. A dispersive and anisotropic realization of the nearly perfectly matched layer (NPML) absorbing boundary condition is adopted in this numerical model for ease of implementation. Earth curvature is included in the model through the modified refractive index method. The surface impedance boundary condition is adopted to treat arbitrary but homogeneous ground parameters. We quantify the errors through dispersion relations, and the solution convergence is analyzed. Comparisons between our simulation, numerical waveguide mode theory, and experimental data validate this model and show its capabilities compared to other methods. Although this FDTD model was developed for the lightning-generated electromagnetic field simulation, it is also applicable for other very low frequency (VLF, 3-30 kHz) and extremely low frequency (ELF, 3-3000 Hz) wave propagation problems.