@Riming electrification is supposed to be the main process that causes lightnings. In this process, it's very important that the sign ofgraupel reverse at -10. That importance has been pointed out by cold room experiment and numerical calculation studies, but now numerical observation and analysis studies on actual clouds are very necessary.
@In the observation, videosondes that were able to measure the shape and the electric charge of particles at the same time, Doppler rader were used. To investigate the electric structure of the thunderstorms, 19 videosondes were launched over Joetsu, Niigata and Tsunakami, Fukui in winter and 14 Videosonde were launched over Melville Island, Australia.
@We could confirm that sign of graupel reverse at -10 in the cloud and electricity of riming electrification. It is found that only coexistence of graupel and ice crystal is sufficient for lightning activities. The results from detailed analysis of Hector showed that tilting tripole structure was characteristic.