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Keywords:

  • winter sprite;
  • winter thunderstorm;
  • winter lightning;
  • sprite morphology;
  • continuing current

[1] VHF, LF, and ELF lightning events, thunderstorms, and surface electric fields related to sprites were observed simultaneously during the winter of 2004/2005 in Hokuriku, Japan. The analysis of these observations enables us to investigate the relationship among sprites, lightning characteristics, and thunderstorm structure just before sprite genesis. Typical winter sprite parent thunderstorms had a mesoscale cloud area with small, embedded convective cells. Positive charges responsible for sprites tend to reside in the upper part of the thunderstorms; only a few positive charges were assumed to be located in the lower part. The total amount of positive charges removed by a sprite-producing flash from the upper and lower parts of the thunderstorms were estimated to be approximately 100 C and as large as 300∼400 C, respectively. Active thunderstorms with lightning accompanied by transient currents tended to generate simple sprites; more complex sprites were excited by lightning with continuing currents, which were generated by a few active thunderstorms and thunderstorms with precipitating stratiform clouds. VHF sources related to sprites can be found in the range of 5 to 72 km. The range of displacement between a sprite element and the corresponding positive cloud-to-ground lightning discharge or the first VHF source was 6∼30 km, and the bottom of the sprite bodies was located between 66 and 74 km. On the basis of these results, we deduced that the complexity of sprite morphology might be attributed to the differences in lightning characteristics.