A possible effect is modeled and discussed on the Schumann resonance records of the giant γ-ray flare from SGR 1806-20. We show that the dayside ionosphere modification is able to cause an abrupt reduction in the power spectra of global electromagnetic resonance. Spectral modifications fade in time, so that the usual and regular patterns are recovered in tens of minutes. An application of signal sonogram is suggested for the signal processing around the time of γ-ray burst, which would facilitate detection of the event.
ULF (0.1-30 Hz) band magnetometer receiver was developed for detecting electromagnetic-wave precursors of earthquakes and volcanic eruption. The receiver attained a high sensitivity of about 1pT/√Hz (10Hz) for ground based observation of the flux anomaly. This paper describes the design and analysis of the induction coil sensor magnetometer. The nonlinear magnetization characteristics of the ferromagnetic Permalloy core are expressed by a negative feedback model in this paper. The sensor performances such as sensitivity are analyzed by the linear model. The sensor performances are measured by the effective cross-section area. The sensitivity calibration method and the test bench are shown by making use of the Helmholtz coil. The minimum detectable flux density is determined by the ambient flux noise density.
ELF (30-300 Hz) band three-axial magnetic-flux receiver was developed for detecting electromagnetic-wave precursor of earthquakes and volcanic eruption. The receiver attained a high sensitivity of 0.4pT/√Hz (223Hz) and 4.5 pT/√Hz (17Hz) for the ground based observation of the ambient magnetic flux anomaly. The receiver was extended to detect ultra-low-frequency (ULF) variation (0.1 to 10-7Hz) of crust magnetic flux by through MMD (Modulated Magnetic-flux Detection) reception. It detects the modulated components of the ELF band atmospheric signal which are produced by the crust ULF magnetic-flux variation. The receiver noise due to the artificial noise can be smoothed out from the objective ULF magnetic flux signal by introducing long term integration for the period of 107 seconds of the detected signal. The receiver detected the ULF anomaly of magnetic variation and the Schumann Resonance variation appeared before the two earthquakes of the class M7 occurred in Japan in 2005 and 2007 respectively.
The amplitude and phase of VLF transmitter signals NWC (19.8 kHz), NPM (21.4 kHz), and NAA (24 kHz) have been monitored at Agra (geomag. lat. 17.10°N, L=1.15), India using AbsPAL receiver for a period of three years between 01 September, 2002 and 30 August, 2005. Seven cases of abrupt amplitude and phase changes have been identified which varied between 3 and 7 dB and 40° and 80° respectively. The onset duration varied around 5 sec. The observed characteristics have been examined in the light of lightning induced electron precipitation (LEP), solar flares, and lightning, and finally attributed to early/slow perturbation caused by distant sprites and lightning along the propagation paths.
Daily variation of vertical TEC data recorded at Bichpuri Agra station (Geographic Lat. 27.2°N, Geographic Long. 78°E, Geomagnetic Lat. 17.10°N) employing a GPS receiver has been studied for a period of three months from 1 April to 30 June 2008 in relation to Wenchuan earthquake (M=7.9) of 12 May 2008. A significant enhancement has been observed in TEC 22 days before this earthquake. This result is interpreted in terms of E×B drift mechanism, where E is electric field of seismic origin. Further, fractal analysis of TEC data has also been carried out using Burlaga- Klein method and it is found that fractal dimension gradually increases long before the occurrence of this earthquake. These results are not influenced by magnetic storms and are attributed strongly to earthquake.