Simulation of the propagation of lightning electromagnetic pulses in the Earth–ionosphere waveguide using the fdtd method in the 2‐D spherical coordinate system

Abstract

The finite-difference time domain (FDTD) method in the two-dimensional (2-D) spherical coordinate system was used to compute waveforms of vertical electric field on the ground surface at distances of 280, 450 and 958 km produced by negative lightning return strokes. The use of the FDTD method in the 2-D spherical coordinate system allowed us to represent the Earth's curvature. Note that the flat-ground approximation is inadequate beyond a distance of 300 km or so. The lightning source was represented by the modified transmission-line model with linear current decay with height (MTLL model). The conductivity of the atmosphere was assumed to increase exponentially with height. Skywaves (reflections from the ionosphere) were identified in computed waveforms and used for the estimation of apparent ionospheric reflection height. It was found that our model better reproduces the electric field waveforms measured at distances of up to about 1000 km by Qin et al. (2017) than the flat-ground model.