Numerical simulation and experimental study of the natural electromagnetic waves in the elf and vlf bands

Résumé

The main motivation of this study is to characterize the natural electromagnetic phenomena occurring in the Earth-ionosphere cavity, with the aim of extracting information from the natural processes which are involved in its generation and propagation. This story starts at the end of the XIX century, with various scientists starting to think on the Earth as a global electromagnetic circuit. A great historical review of the beginnings of this topic was made by Besser [2007]. The study of the electromagnetic natural noise recovered its interest with the work by Williams [1992], who related the Schumann resonance parameters with the global temperature, setting the basis to study the global climate by means of the electromagnetic natural emissions. Recently, several studies prove that these phenomena can be employed for prediction of natural disasters like earthquakes or volcano eruptions, e.g. Hayakawa [2006]. We perform two independent experimental studies based on the measurement of these signals on a large time scale (in the order of years). Time series recorded at ground level are employed for the first study, and records from DEMETER satellite are analyzed in the second. Signals in the Extremely Low Frequency band, 3 Hz - 3 kHz, and in the VLF band, 3 kHz - 30 kHz, are discussed in this dissertation. Then, a way to model the full 3D Earth-ionosphere cavity by means of TLM method is presented. The model employes parallelization techniques, due to the memory and computation requirements to model the problem. The model is validated through comparison with analytical solutions to simplifications of the real cavity, as well as results from experimental measurements of the modeled phenomena. Finally, the first results obtained with this tool are presented, like for instance the effect of an atmospheric disturbance on the SR, or the implications of the day-night asymmetry of the cavity.