抄録
In July 2008, 5 people died by flash flood at Toga River in Kobe. This tragic disaster was brought by suddenly generated and developed isolated cumulonimbus cloud. This type of rainfall is called “Guerilla-heavy rainfall” in Japanese media reports. In this event, the water level was suddenly rose in just 10 minutes, so it's quite important to predict the risk of heavy rainfall even within a few minutes. Nakakita et al. developed the risk prediction system using vertical vorticity information inside the baby cell aloft. Baby cell is the first echo observed by radars aloft. However, it is unclear why baby cells having large vorticity grow to heavy rainfall. Thus, we tried to verify the mechanism of generating and developing process of the cells. First, we found not only positive but also negative vorticities in the baby cells, and found vertical vortex tubes inside the cells. Next, we analyzed a high ZDR column in one event, and discovered vorticity associated with convective updraft.
