In this paper, I made a brief review on the earthquake-related electromagnetic study in China, especially focusing on geo-electromagnetic observation and empirical prediction based on the observation data. After introducing briefly the roles of China Earthquake Administration (CEA) in seismo-electromagnetic study in China, I summarized various electromagnetic observations (e.g., apparent resistivity, geoelectric potential, geomagnetic field, electromagnetic disturbance, etc.). As the potential application, I showed the cases of the empirical prediction based on the observed electromagnetic data associated with some earthquakes in China. This paper may provide some useful information for those who want to know the general situation of seismo-electromagnetic study in China.

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We have observed and recorded the neutral current of a 500 kV transformer at a substation in Chubu region since 2008 in order to detect electromagnetic anomalies associated with earthquakes. In this observation, we could not find any particular anomalous change of the neutral current before and after earthquakes (e.g. The Suruga Bay Earthquake occurred on August 11, 2009).
However, from the result of a quantitative analysis between geomagnetic field data and neutral current data, we would be able to investigate the underground electric conductivities near the substations. It would be possible to monitor the change of electromagnetic structure of underground before and after earthquakes.

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The purpose of this paper is to review the seismogenic effects in the ELF (extremely low frequency) Schumann resonance (SR) band. Two interesting phenomena have been recently observed in this ELF SR band. The first is the enhancement of the SR third or fourth harmonic prior to a large earthquake (EQ), and the second is the excitation of SR-like line emissions possibly related with large EQs. The first phenomenon was initially found as the enhancement of the SR fourth harmonic in Japan, in possible association with the famous 1999 Chi-chi EQ in Taiwan. This was further statistically confirmed on the basis of data during several years and was additionally confirmed by further observations at a different place in Japan. The second SR-like line emissions have been detected in Japan in possible association with two huge EQs in Japan. The frequencies of those line emissions are likely to be shifted from the conventional SR harmonics by a significant amount of 1∼2 Hz, but their temporal variation seems to suggest a close relationship with the conventional SRs. Together with the explanation of the observational evidence of those two phenomena, we provide the plausible theoretical explanation of those phenomena. The first anomaly is interpreted in terms of the wave interference due to the significant difference in propagation length between the direct signal from the American lightning source and that scattered by the seismo-ionospheric perturbations above the epicenters of EQs in Taiwan. The second phenomenon is recently interpreted in terms of the ground detection of gyrotropic waves in the ionospheric dynamo region, being excited by the seismogenic noises from below in the ELF SR band.

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The ionospheric anomaly prior to the 2007 SouthernSumatra earthquake (M8.5) was observed by GPS receivers around Sumatra islands. In this paper, to investigate the three-dimensional structure of electron density in Ionosphere, a tomographic approach (Residual Minimization Training Neural Network; RMTNN) has been performed. The results of the tomographic approach are consistent with those of total electron content (TEC) approaches. We found that the significant decreases take place in the heights of 250-400 km, especially at 330 km height. But the height which gives the maximum electron density is not changed. The obtained structure is that the decreased region exists in the southwest side of Integrated Electron Content (IEC) (400-550 km altitudes) and in the northern side of IEC (250-400 km altitudes). Global tendency of the decreases area is expanded to the east with an altitude and it is concentrated in the southern hemisphere of over the epicenter. These resultsshow that the high capability of RMTNN method for the estimation of the ionospheric electron density distribution possibly associated with earthquake.

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By using multiple reference stations, we have developed a method to get reliable ULF global geomagnetic variations. This background is extremely useful for detecting local anomalous behaviors. This paper demonstrates developed variable tools to identify the anomalies in two frequency ranges; daily variation and 10-1000 seconds. For estimating background daily variations, the periodical model has been applied for data observed at 3 reference stations and a study station. Comparison between the first principal component of the periodical data from the reference stations and the periodical data derived from the target station provides high correlation in general. For data with 100 sec periods after wavelet filtering, the nighttime energy variations have been investigated among 3 reference stations and a study station. The similar principal component analysis as the diurnal variation has been performed and results also show high correlation between the variation at the target and the global background. These tendency suggest that the developed two methods are effective to identify the anomalies in automatic. Examining the original data, we can know details of waveform and distinguish whether the anomalies is related to underground activities or just some artificial noises.

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The Maido-1 satellite observed the lightning discharges from February to October, 2009. We analyzed the observational results with the Maido-1 satellite above Southeast Asia area and the Atlantic Ocean area. First we calculated the change of the pulse width with the electromagnetic wave propagation in the ionosphere. The numerical calculation indicates that the full width at half maximum (FWHM) is changed by the incident angle to the ionosphere. The FWHM increases to tens of nanoseconds through the ionosphere. Next we compared the pulse widths of the received pulses by the Maido-1 satellite in the Atlantic Ocean area and Southeast Asia area. The results in the Atlantic Ocean area have the greater FWHM than those in Southeast Asia area. On the other hand, the results of World Wide Lightning Location Network (WWLLN) indicate that the distance between the position of the radiation source and the observation site in the Atlantic Ocean area is longer than in Southeast Asia area. The calculation results can explain two observational results (the maido-1 satellite and the WWLLN). Then we discussed the relationship between the number of the received pulses and the lightning activity level. From the analysis of the detected number by the WWLLN and the received pulse number by the Maido-1 satellite, the more active the lightning discharges are, the more VHF pulses are radiated.

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The purpose of this study is to demonstrate the usefulness of the Doppler Radar for Airport Weather (DRAW) system as a research tool for studying typhoon. I particularly aim at assessing opportunity for detecting typhoon inner core circulations and precipitations with the DRAW. For centers of typhoons, which correspond to positions of the inner cores, it is estimated that 322 hours of data (61cases) had been collected with the eight DRAWs over past 30 typhoons (1995-2005). On average, about one typhoon will be observed with each DRAW site. The Naha DRAW (the southernmost DRAW site) will provide the most frequent observations and each observed center would remain in radar range for periods between 4 and 11 hours. In this study, it is shown that many typhoon inner core cases will be collected with DRAW and suggested new opportunities for further research and development these phenomena. DRAWs will play an increasing role to understand detailed typhoon structures and life cycles (e.g., polygonal eyewall, mesovorticies, landfall processes, and asymmetric structure), and in the future, to improve typhoon intensity forecasts.

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We have been developing EM source location system in VLF/LF bands based on broadband digital interferometry to monitor lightning activities in a wide area. Since EM waves in VLF/LF radiated by lightning discharges propagate a long distance, the VLF/LF interferometer locates lightning discharges a few hundred kilometers away from the VLF/LF interferometer. We conducted lightning observation campaign by a prototype of a VLF/LF band digital interferometer and VHF band digital interferometers in Darwin, Australia. Horizontal distances between VLF/LF and VHF band locations show that VLF/LF radiation sources were located near those of VHF source. We succeeded in locating VLF/LF radiation sources associated with return strokes near the ground.

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A sprite campaign was conducted in the Hokuriku area of Japan during a winter of 2004/2005. On the basis of a combined analysis of the data from various instruments (CCD cameras, radar, VHF/LF∼MF lightning mapping system, field mill network, and ELF detector), we studied meteorological and electrical structures for winter thunderstorms and sprite-producing positive discharge. Typical winter sprite parent thunderstorms had a meso-scale cloud area with embedded small convective cells. Some small winter thunderstorms accompanied by the most frequent sprite events were found to cause 2∼3 sprite events during a short interval of about 3∼5 min. When the sprites were observed, the extent of the convective cells at 20 dBZ counter was atmost ∼20 × 20 km. The VHF sources associated with sprites were located near south of the convective cell and were mapped within very small areas of at most ∼10 × 10 km. This fact shows that some small winter thunderstorms can generate large positive charge associated with sprites. We will present the analysis of such a small thunderstorms with sprites and positive lightning discharges.

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As accuracy of satellite precipitation estimates improves and observation frequency increases, the applicability of those data to a more variety of societal benefits as well as climate studies is expected to enhance. To meet those users' needs that higher temporal resolution is desired with near-real-time availability, we are developing and operating the “JAXA Global Rainfall Watch” system, which produces hourly global rainfall map data in 0.1 degree grid resolution, and disseminates it four hours after observation. The algorithms are based on the achievement of the Global Satellite Mapping for Precipitation (GSMaP) project, which combined observation data from microwave and infrared radiometers aboard multiple satellites. The interests of GSMaP users cover broad fields and world wide. Several activities to apply GSMaP data to some flood warning systems are underway. Validation with Japanese Radar-AMeDAS rainfall analysis data for 2009 shows correlation coefficients higher than 0.5 during rainy season, but lower values around 0.3 or 0.4 during winter season with less rainfall. GSMaP is a proto-type for the Global Precipitation Measurement (GPM) mission in 2013, and challenges and possibilities of new application are explored.

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Geoelectrical fluctuations are the end product of several geophysical phenomena. In particular geoelectrical signals measured in seismically active areas can be attributed to stress and strain changes, associated with earthquakes. In order to study the geoelectrical potential difference changes associated with the earth's crustal activities, it is important to discriminate from other noises because they are generally weak. The complexity of this problem has suggested the development of advanced statistical methods to investigate the heterogeneous nature of these fluctuations. In this paper we analyzed the time dynamics of short-term variability of geoelectrical field measured at Kiyosumi station, located in southern part of Boso peninsula, Japan. We tried to apply principal component analysis (PCA) and singular spectral analysis (SSA) to detect and reduce precipitation effects which are the most intense noise in geoelectrical potential difference data. The results show an application of PCA to two orthogonal electric data can detect the precipitation and SSA has a potential to remove the precipitation effects.

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VLF (Very low frequency; 3-30 kHz) wave propagation in the Earth-Ionosphere waveguide can be simply analyzed by the method developed in this paper. The finite-difference time-domain (FDTD) method is used with a conductivity tensor to model the Ionosphere, and the applicability is limited in monotonic cases. The proposed method is compared with the wideband one, and it is concluded that the developed method can be used as the VLF wave simulator without errors. Moreover, the conformal FDTD is introduced to consider the curvature of the Earth's surface, and we have clarified the difference between the two-dimensional modeling in the Cartesian coordinates and the cylindrical ones.

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Earthquake-related anomalous electromagnetic phenomena have been reported in various frequency ranges in a few decades. Investigation on the anomalous propagation of VHF transmitter waves is one of promising approaches on the short-term prediction and crustal activity monitoring. The anomalous propagation is considered to be generated by disturbances of the atmosphere above the epicenter or along the propagation path prior to large earthquakes. Consequently, over-horizontal propagation has been received. A recent study shows that the appearance of anomalies was significantly enhanced within 5 days before earthquakes with M ≥ 4.8. However, there is no information on the scattered place, that is, the direction of wave arrival. Therefore, a simple interferometer system for VHF radio wave to identify the position between space-time of earthquake-related atmospheric disturbances has been developed and installed at Chiba University. In this paper, we will show you the developed interferometer system and results of fundamental tests to evaluate the performance of developed and installed interferometer at Chiba. In addition, facts on invisible propagation of VHF radio wave obtained from 1-year continuous measurement at Chiba are described in this paper. Those are possible radio duct propagations and possible earthquake-related anomalous propagations.

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The decomposition characteristics of an artificial biogas, which is a mixture of CH₄, CO₂ and H₂S, using a low pressure DC glow discharge have been investigated. It is found that H₂, CO, C₂H₂, H₂O, CS₂ and COS are produced from the artificial biogas in the glow discharge. About 65 % of hydrogen atoms in CH₄ are converted into H₂ at the input energy of 800 J, at which CH₄ is completely decomposed, and the decomposition characteristics of the artificial biogas has little dependency on H₂S additive. Farther, H₂S has a tendency to be decomposed earlier than the other components of the artificial biogas. When the glow discharge is generated in the artificial biogas with H₂S, some of carbon atoms are found to deposit on electrodes and the wall of a discharge chamber.

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In recent years, the superannuated transformers have been increasing. This causes such problems as requiring the maintenance of diagnosing internal abnormalities of a transformer and carrying out condition assessment. One of the ways to assess the internal condition is a gas analysis of the insulating oil. In this analysis, low-temperature overheating, the pre-phenomenon of the abnormal heating in the transformer, can be detected. Finding and dealing with this abnormality at the early stages reduce the risk of transformer failure. However, evolved gas of this analysis shows different patterns depending on the existence or non-existence of oxygen.

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Electrochemical migration growth along the thickness direction in a two-layered dielectric, consisting of an Al cathode, paper/phenol-resin composite, epoxy resin, and a Cu anode that simulates a laminated structure of a printed wiring board, was detected by the pulsed electroacoustic (PEA) method. The PEA signals obtained were analyzed using a numerical model on the generation and propagation of acoustic waves. Accumulation of positive charge appears in front of the Cu anode of the sample, in which the growth of electrochemical migration was observed by SEM-EDS. At the same time, the signal due to negative charge at the interface between the resin and the composite decreases significantly. This is ascribable to the progress of electrochemical migration in the thickness direction. The numerical analysis done by assuming that the conductivity of the epoxy resin layer near the anode was increased gives a good agreement with the PEA spectra. As for the charge on the anode, the PEA signal appears at the correct position when the anode material is semi-conductive polymer, while it appears as if the anode were inside the real anode when the material is Cu. In order to solve this puzzle, numerical calculations were carried out by the finite difference method. As a result, it has become clear that the discontinuity in the acoustic impedance between the epoxy resin and Cu electrode is responsible.

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This paper deals with charge-up characteristics of printed circuit (PC) board materials due to electrons penetrating inside a spacecraft body. Glass-fiber-reinforced plastic (GFRP) plates, typical PC board material, were irradiated by electron beam with the energy lower than 20keV simulating decelerated high-energy electrons penetrating through the satellite skin. The charge-up characteristics were obtained as parameters of irradiation time, the energy and the current density of the electron beam. The volume resistivities of the GFRP plates were also evaluated by the decay time constants of the surface potential after electron irradiation. The influence of a protective coating on the charging of the GFRP plates was also tested.

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It is crucial for proper insulation design of cast resin transformer to consider voids and delamination which might exist in cast molding because of several surface boundaries between resin and conductor. Such defects in the insulator lead to reduction of the life of the apparatus. In this report, we investigate the relation between the void size and apparent charge of partial discharge (PD) occurring in a model simulating the insulation system of cast resin transformer. It is also important to determine necessary PD detection sensitivity of PD test in a factory as well as in a field. In this paper, we also discuss the detection sensitivity by considering the relation between charge and void radius using formula derived by L. Niemyer, M. Pedersen and their colleagues in the late 1980's to apply to the case of the cast resin transformer. Experiments were also performed to obtain PD inception voltage (PDIV) of epoxy resin slab including an artificial void with a given size. Investigation was also made on the effect of X-ray irradiation to the epoxy resin on PDIV characteristics.

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Power modules are often molded with a resin, such as epoxy, for their protection and downsizing. The resin, which contains inorganic filler, is usually non-transparent. As optical inspection is not realistic, non-destructive inspections using X-ray or ultrasound is being performed. As for cracks and so-called “electrical tree” in the insulation, ultrasound may bring a good contrast, because there is a big difference in acoustic impedance between resin and air.
There are some reports on ultrasonic observation for electrical trees, however, as thick specimens were employed, the spatial resolution was very poor due to the limitation of available frequency range. However, the diameter of electrical tree path is as thin as 5 μm. Enough resolution can't be obtained by the measurement with a low frequency range. Based on the above background, we tried to observe a “close but small” tree by ultrasonic imaging. Using the wide-band ultrasonic microscope, it was examined if a tree with 0.5 mm in scale could be observed with its fine structure.
An ultrasonic image, in which branching in the tree can be discriminated. The spatial resolution was determined as 40∼50 μm. An image processing was carried out in order to acquire a clearer image. Assuming the Gaussian as a blur function, the original image was deconvolved.

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To evaluate time variation of hydrophobicity of silicone rubbers used for outdoor polymeric insulators, various kinds of test methods have been suggested. CIGRE WG D1.14 conducted an international Round Robin Test (RRT) to clarify the efficiency and reproducibility of Dynamic Drop Test for the evaluation of hydrophobicity stability of the materials. Three Japanese universities were participated the RRT and had contributed much for the activity. This paper provides the outline of CIGRE RRT and typical experimental results of the Dynamic Drop test.

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We have observed space charge profiles in cross-linked polyethylene (XLPE) under dc high electric field using the PEA (pulsed electro-acoustic) system to study the relationship between space charge behavior and dielectric breakdown. In our previous research work, we have found that a large amount of, so called, packet-like charge generates in low density polyethylene (LDPE) under high dc electric field of more than 100 kV/mm. The packet-like charge enhances the electric field locally in bulk of the sample, and then finally it leads a breakdown. On the other hand, a new type of XLPE which was made through adding conductive inorganic fillers, shows a good dc dielectric breakdown characteristic and high volume resistivity under dc stress. In this report, we tried to observe the space charge behavior under high dc electric field in this material. From the results, it is found that the charge injection is effectively suppressed by adding only a small amount of conductive inorganic fillers to XLPE.

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