Schumann resonance observation in China and anomalous disturbance possibly associated with Tohoku M9.0 earthquake

Schumann resonance (SR) is an electromagnetic resonance phenomenon in the Earth-ionosphere cavity exited by global lightning activities when the wavelength matches the circumference of the Earth, and the lowest four peak frequencies of SR are about 8, 14, 20, and 26 Hz. This article presents the new observational data of SR in China. The observations of two horizontal magnetic components (<i<B</i<<sub<NS</sub< and <i<B</i<<sub<EW</sub<) in the frequency band range of 3-29 Hz at Yongsheng observatory (26.7°N, 100.8°E) in southwestern China were mainly analyzed. It is found that the SR amplitudes at peak frequencies in <i<B</i<<sub<NS</sub< and <i<B</i<<sub<EW</sub< components all showed diurnal and seasonal variations, and that the SR amplitude in <i<B</i<<sub<NS</sub< component is always higher than that in <i<B</i<<sub<EW</sub< component. Diurnal variation of SR amplitude around equinoxes and solstices in <i<B</i<<sub<NS</sub< component is related to active intervals of three global thunderstorm centers, while SR amplitude in <i<B</i<<sub<EW</sub< component is the most significant at around 16 LT, corresponding to Asian center. SR amplitudes both in <i<B</i<<sub<NS</sub< and <i<B</i<<sub<EW</sub< components increase in the rainy season from May to September. In addition, the SR anomalies in association with the 2011 Japan earthquake are exhibited. The anomalous effect was characterized by an increase in amplitude at the lowest four SR modes beginning at 4 days before this earthquake. Upon analyzing the wave interference between the direct wave and disturbed wave scattered by localized modification of lower ionosphere over the epicenter, Asian and African thunderstorm centers are found to contribute to anomalous effect observed at Yongsheng station. Modeling results of SR regular and disturbed spectra at different local times led to the similar conclusion.