Observation of sprites over the Sea of Japan and conditions for lightning-induced sprites in winter

Abstract

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.

How do winter thundercloud systems generate sprite‐inducing lightning in the Hokuriku area of Japan?

“…Several images of column-form sprites [Hayakawa et al, 2004] were captured at 10:37:59.36 UT on 11 January 2005. In addition, the sprite-parent lightning discharges and their thunderclouds were observed with the weather radar, the SAFIR and the field mill network.…”

“…Eleven of these fifteen events are found to exhibit similar characteristics to those for one particular event presented in this paper. Hayakawa et al [2004] have shown that self-organization may be essential for the generation of sprite parent thundercloud systems. This conclusion is further supported by this report based on combined use of different observations including weather radar, SAFIR, and the GOES-9 satellite.…”

“…The results of our analysis suggest that the sprite-inducing +CG would be triggered by the long lightning channel accompanied by large positive charge transfer. Hayakawa et al [2004] investigated the fine structure of winter thundercloud systems with a fractal analysis of the radar echo. They concluded that spriteinducing lightning could be generated because many thunderclouds were connected with each other in the sense of self-organization.…”

“…The cloud size associated with the À20°C isotherm was between 8,500 and 40,500 km 2 , which was smaller than the usual sprite-parent summer MCSs (greater than 20-25,000 km 2 ) in large continents [Adachi et al, 2005]. Hayakawa et al [2004Hayakawa et al [ , 2005 discussed why such small winter thundercloud systems are able to generate spriteinducing lightning. They concluded that many small thunderstorm cells were connected with each other and the connection enabled large electric charge transfer to induce sprites.…”

Underlying mechanisms of transient luminous events: a review

“…The carrot type sprite contains diffuse tops and lower tendrils extending down to altitudes of 30-40 km, while the columniform sprite has a very fine spatial structure as compared with the "carrot" sprite (e.g. Hayakawa et al, 2004;Wescott et al, 1998). The faint red glow diffusion region lies in the altitude range 85 to 90 km, while the brightest region occurs in the 65-85 km altitude range.…”