Research On Electromagnetic Properties In The Earth-ionosphere Waveguide System

In this thesis, the electromagnetic resonant phenomenon, namely Schumann Resonances (SRs)which are excited by the extremely low frequency (ELF)/Ultra low frequency (ULF) electromagneticwaves within the Earth-ionosphere waveguide system, are studied. Researches on the SRs in resentyears indicated that the SRs are related to global lightning storm activities, D-layer monitoring, spaceweather and global climate change, etc. In this thesis, a polygon mesh modeling method and a threedimensional Finite Difference Time Domain (3D-FDTD) method are developed to model and studythe propagation of ELF/ULFelectromagnetic waves in the Earth-ionosphere system. The maincontents and innovations are as follows:1. Based on the polygon mesh modeling method and the3D-FDTDmethod, we have constructed a3D geometric model for the Earth-ionosphere waveguide system. Based on this model, we havededuced the FDTD discrete iterative equations from the Maxwell integral equations. After that,we have validated the correctness and effectiveness of the model under different simulationconditions.2. Geological information and ionosphere conductivity information are merged into the3Dgeometric model. Simulation results prove that the constructed model is very efficient for studythe propagation of ELF/ULF electromagnetic waves in the real Earth-ionosphere waveguidesystem.3. Prony’s method is introduced to extract the SR parameters (including resonant frequences fnandquality factors Qn) from the time domain data of ELF/ULF electromagnetic waves.4. Analytical values of the ionosphere conductivity are employed to study the SR variations duringsolar proton events and X-ray bursts. The related analysis indicates that the frequency of the firstSR mode decreases during SPEs and increases during X-ray bursts, in agreement with previousresearches and observations.5. Simulation model along with asymmetric conductivity profiles derived from InternationalReference Ionosphere (IRI) is used to model the diurnal and seasonal variations of the SRs.Besides, the SRs variations during the past three decades are also simulated based on the modeltogether with the inonsphere conductivities, and the results are compared with sunspot number cycle. Finally, predictions for variations of the SR parameters in the next eleven years (solarcycle) are made.