This paper presents a phenomenological idea about lightning flash to share the back ground understanding for this special issue. Lightning discharges are one of the terrible phenomena, and Benjamin Franklin has led this natural phenomenon to the stage of scientific investigation. Technical aspects like monitoring and location are also summarized in this article.

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The purpose of this paper is to review the previous direction finding (DF) systems including goniometer, field-analysis method and also we demonstrate how important these DF techniques are in the general studies of VLF/ELF sferics and whistlers. We have presented some latest findings such as new results on ELF transients (charge moment change) and convincing evidence on the ducted propagation of low-latitude whistlers.

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This paper presents an analysis of lightning-induced magnetic fields in a building. The building of concern is protected by the lightning protection system with an insulated down conductor. In this paper a system model for metallic structure of the building is constructed first using the circuit approach. The circuit model of the insulated down conductor is discussed extensively, and explicit expressions of the circuit parameters are presented. The system model was verified experimentally in the laboratory. The modeling approach is applied to analyze the impulse magnetic fields in a full-scale building during a direct lightning strike. It is found that the impulse magnetic field is significantly high near the down conductor. The field is attenuated if the down conductor is moved to a column in the building. The field can be reduced further if the down conductor is housed in an earthed metal pipe. Recommendations for protecting critical equipment against lightning-induced magnetic fields are also provided in the paper.

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The sprite campaign was conducted by the sprite research group of University of Electro-Communications (UEC) during the winter of 2001/2002. On 14th December 2001, nine sprites were observed from Shimizu in Shizuoka and ELF transients were measured at Moshiri in Hokkaido. One of the sprites was also observed by the weather radar and the field mill network around the Komatsu Air Base. The sprite parent thunderclouds associated with the positive cloud-to-ground flash (+CG) were investigated with special reference to their electrical and meteorological characteristics. The results are summarized as follows; (1) The sprite parent thundercloud was very small (horizontal scale is at most 30 km) and the sprite was generated by a single flash when the thunderclouds were dissipating just after the maximum activity. (2) The sprite parent +CG occurred under the stratiform region of the thunderclouds. (3) Before the sprite causative +CG occurred, very large positive charge and negative one were found in and over the thundercloud by the analysis of sequential field mill observation.

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This paper focuses on the effects of the interface between epoxy resin and nano- or micro-scale silica filler. Experiments were carried out on epoxy resin containing nano- or micro-scale silica fillers (nano-composite or micro-composite) to investigate the effects of the epoxy/filler interface on the properties of water absorption, electrical insulation and fracture toughness. The results indicated that epoxy/silica filler interface has an impact on the properties of the nano- and micro-composites. Nano-composites were shown to have higher water absorption than micro-composites because water accumulated over a larger interface area. Moreover, the nano-composites with interfaces treated with a silane coupling agent showed insulation breakdown properties and fracture toughness superior to those of the base epoxy resin and the micro-composites. The chemical bonding by the silane coupling agent at the epoxy/nano-scale silica filler interface played a more important role in water absorption and insulation breakdown properties than for the micro-scale silica filler. The filler size reduction to nano-scale needs appropriate interface treatment because of its tremendously large interface area. In addition, belt-shaped area models demonstrated the improvement of insulation breakdown properties and fracture toughness from the viewpoint of encountering frequency between electrical treeing or initial cracking and fillers. It is assumed that an increase in encountering frequency prevents treeing or cracking from propagating efficiently and thus improves insulation breakdown properties and fracture toughness in the nano-composite.

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