Analysis Of Lightning ELF Electromagnetic Wave Propagation In Earth-Ionosphere Waveguide

The study of propagation characteristics of lightning ELF waves plays an important role in the global circuit balance and upper atmospheric photochemical effect, as well as the distribution and disturbances of the ionosphere dielectric media, global lightning activity and climate change and so on. In this paper, we focus on the propagation effects of the lightning ELF waves in the Earth-Ionosphere system, and use three-dimensional spherical coordinates finite difference time domain (FDTD) method to build the Earth-Ionosphere lightning electromagnetic model considering the nonlinear characteristics of ionosphere dielectric media. Furthermore, we present a comparison analysis of the propagation of Q-burst from the super lightning and its SR background signal characteristics by using our simulation results and the obtained experimental data. The main research work and the conclusions in this paper are as follows:1) The lightning ELF waves at different distances are the results of the direct wave, antipodal wave and the world-round periodic wave which overlap with each other. The lightning ELF waves exhibit different waveform characteristics and depend on the source to observation distance (SOD). When the Earth-Ionosphere waveguide cavity is ideal and lossless, the lightning ELF waves will not attenuation and have phase reversal phenomenon at the spherical symmetrical position of the lightning source. When the Earth-Ionosphere waveguide cavity is lossy, the amplitude of antipodal wave and the the world-round periodic wave are attenuated by the present of the ionosphere lossy media until disappear.2) Different distribution of the ionosphere dielectric media have similar effects on the time-domain waveform of lightning EM fields, but there are some differences in the fields amplitude. The character of the frequency spectrum depends on SODs:(1)When SOD is 5Mm, the vertical electric field (Ez) using the single-exponential and ’Knee’ shape height profile of the ionosphere conductivity have three spectrum peaks of SR, but those consider the ionosphere conductivity by following double-exponential profile have five SR peaks;(2) When SOD is 10Mm, the frequency spectrum are found to have three spectrum peaks of SR for all the three different height profiles of the ionosphere conductivity;(3) When SOD is 15Mm, the frequency spectrum of Ez considering the double-exponential and ’Knee’ shape height profile of the ionosphere conductivity have double SR peaks, but those corresponding to single-exponential conductivity profile have four SR peaks.3) The simulated Q-burst have excellent agreement with the experimental data. The SOD is estimated for classifying the types of Q-busts:V, W, Double V and three-pulses.The simulated frequency spectrum have similar characters with the experimental data especially below 10Hz, which will attenuate rapidly in the high frequency part (>100 Hz or so). It is noted that, after comparison our computed Q-burst of the magnetic field in East-west and South-North direction with experimental data, the ionosphere conductivity profile might have double-exponential profile characters for this case, and the super lighting related this Q-burst is estimated to occur at one of three main thunderstorm regions of global lightning activity-Southeast Asia area.