Characteristics of the Sprite Parent Winter Thundercloud with Positive Single Flash in Hokuriku, Japan (A Case Study on 14th December 2001)

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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.