The subionospheric VLF/LF propagation is extensively used to investigate the lower ionospheric perturbation in possible association with earthquakes. An extensive period of data over 7 yr from January 2001 to December 2007 and a combination of different propagation paths in and around Japan are used to examine the statistical correlation between the VLF/LF propagation anomaly (average nighttime amplitude, dispersion, and nighttime fluctuation) and earthquakes with magnitude >6.0. It is then found that the propagation anomaly exceeding the 2σ (standard deviation) criterion indicating the presence of ionospheric perturbation is significantly correlated with earthquakes with shallow depth (<40 km). Finally, the mechanism of seismoionospheric perturbations is discussed.

C), whereas a large lightning peak current (+223-+470 kA) (or slow-tail amplitude) leading to the strong EMP is necessary to initiate elves, but with rather small ionospheric disturbances.

[1] Gamma radiation observed in space has been associated with lightning flashes in thunderstorms. These special flashes do not appear to be the large and energetic positive ground flashes that also produce sprites. Considerations of gamma ray attenuation in air indicate that such flashes may not produce gamma radiation at sufficient altitude to enable their escape to space. High-altitude intracloud lightning, most prevalent in the tropics where the tropopause is also high, may be a necessary source.Citation: Williams, E., et al. (2006), Lightning flashes conducive to the production and escape of gamma radiation to space,

We have succeeded in observing sprites for winter lightning in the Hokuriku area (Japan Sea side) of Japan in the winter of 2001/2002. The optical results on three days are compared with the corresponding characteristics of parent (causative) lightning with particular attention to the significant diferences between Hokuriku winter lightning and the more widely studied continental lightning. Despite significant differences with Hokuriku winter lightning. We have found nearly the same sprite properties as already observed in the US. continent with a signiJicant difference (simpler shape for Hokuriku winter sprite). Then, we have also discussed the criteria for sprite occurrence. Specifically, two similar criteria are found: ( I ) cloud-to-ground discharges of positive polarity and (2) the presence of a certain threshold in vertical charge moment(2000-300C km) (roughly consistent with that for the U.S. continent ). Mesoscale convective systems are not necessary to store the charge necessaly for sprites, but the parent Hokuriku winter clouds are substantia& smaller than the minimum scale for sprite occurrence in the continental lightning, but it is larger in area than ordinaly summer thunderclouds. However, there may exit another condition such as clustering or self-organizing effect of thunderclouds for sprite production.

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