The Analysis Of Asymmetry Of Schumann Resonance Spectrum Based On FDTD Method

Schumann Resonance(SR) was a specific electromagnetic wave resonance in the Earth-ionosphere cavity, the propagation of which reflects the distribution of thunderstorm sources and the variation of the ionosphere in the whole cavity. Research showed that the power spectral of SR was an asymmetrical curve, which caused by the interaction of the standing wave and the traveling wave. This paper is to discuss the possibility of the symmetry property about SR spectral with simulated and observed data.First of all, the extremely low frequency(ELF) radio wave propagation is simulated in the cavity with different conductivity model based on three-dimensional FDTD method on condition of excited with only one current source, from which we got the resonance frequency and amplitude which was sampled at nature resonance frequency about the eclectic field. After that source-observer distance(SOD) dependence is studied for mode frequencies amplitude and Q-factor. Conclusions were, 1) between mode’s two adjacent nodal points the resonance frequency was larger with the increase of SOD, while the amplitude was reducing; 2) near the source and the antipode the amplitude had larger value than the other places; 3) the resonance might disappear round the nodal points; 4)And then, three different Lorentzian technique(classic, complex and asymmetrical) for power curves was carried out, in which got the fit error, resonance frequency and Qfactor for different resonance mode at various SODs. Result showed that, the asymmetrical method had an error less than 3% which was smaller than the other two methods, meanwhile most of classic method’s results were between 5% and 10%; the frequency had a different result with the increase of SOD, the error with simulated result was larger near the nodal than those near antinodes; the fit error of Q-factor along the path coming through the antipodes just like the frequency, in each mode had a range about 50% round the experience ones, and reduced to 20% near the antipode; the symmetry properties was independent from the conductivity model, meanwhile it behaved same way just like the frequency at places near sources while the source placed at pole, and approached to zero when close to antipode. At the same time at different source places the symmetry parameter had the same variation.At last, applied the fit method on observed data and extracted the propagation parameters. The asymmetrical method had the smallest error among all the three method, which was less than 7%; the range of first mode frequency was smaller than the others, and the classic method had a stable result in each mode; and for the Q-factor, the first two modes were more stable, e.g. the first mode had a range of 1 to 5, the complex and asymmetrical method had a great change in the other two mode; about the asymmetrical parameter had similar curve at first three mode.