Model Simulation of Very Low-Frequency and Low-Frequency Lightning Signal Propagation Over Intermediate Ranges

A model simulation for very low-frequency and low-frequency lightning signal propagation over ranges of hundreds to a couple of thousand kilometers is presented in this paper. The model is a composite of ground and ionospheric-reflected waves. The ground wave is modeled over a spherical earth that has a finite conductivity. The ionospheric-wave simulation is based on a recently developed full-wave model that treats the lower portion of the ionosphere as a magnetized, anisotropic, collisional, and cold-electron medium. In this paper, only the first-hop ionosphere reflection is presented, although higher order reflections can be readily implemented by the model. For the purpose of demonstration, the modeled results are compared to actual observations of negative cloud-to-ground strokes at various distances for day and nighttime. The model itself, however, can be used for any type of lightning discharge event, including the incloud events that occur above the ground. This model, together with multistation Los Alamos Sferic Array measurements of lightning discharges, might provide an alternate means for monitoring the temporal and spatial variations of the lower portion of the ionosphere.