FDTD Computation of Ground-Level Electric Fields Generated by CIDs at Both Far and Close Ranges

Using the finite-difference time-domain method for solving Maxwell's equations, we computed ground-level electric fields generated by compact intracloud discharges (CIDs) represented by an elevated vertical low-conductivity cylinder at both far (essentially radiation field) and close (other than radiation field components are significant) ranges. The cylinder had a length of about 2000 m, a radius of 100 m, the permittivity and permeability equal to those of vacuum, and the electric conductivity of about 10−5S/m. The cylinder was placed at an altitude of about 14 km above ground, energized at its midpoint, and resultant vertical electric fields on the ground surface were computed at horizontal distances of 2 to about 74 km. A reasonably good match with the corresponding waveforms (NBE #92) measured by (Karunarathne et al, 2016) was obtained for an adjusted excitation voltage waveform specified using the Heidler function with a 10-to-90% risetime of about 6μs. The new results, extending our previous study (Ueda et al, 2025) to close distances, indicate that representation of CIDs by a low-conductivity cylinder allows one to reproduce the measured electric field signatures of CIDs at both far and close ranges.