FDTD Analysis of ELF Wave Propagation in Inhomogeneous Subionospheric Waveguide Models

Abstract

The space formed by the ground and ionosphere is know to act as a resonator for extremely low frequency (ELF) waves. Lightning discharges trigger this global resonance, which is known as Schumann resonances at the frequencies of 8, 14, 21 Hz etc. Even though the inhomogeneity (like day-night assymetry, local perturbation etc.) is important for such subionospheric ELF propagation, the previous analyses have been always made by some approximations because the problem is too complicated to be analyzed by exact full-wave analysis. This paper presents the first application of the conventional FDTD method to such subionospheric ELF wave propagation, in which any kinds of inhomogeneities can be included in the analysis, to be compared with the observational results. We show the application of FDTD to our problem and present a few numerical computational results to be compared with those by the pre-existing analysis method.