Studies on Formation Mechanism of Vertical Vortex Tube inside Cumulonimbus Cloud for Accuracy Improvement of Guerrilla-heavy Rainfall Prediction

In Japan, the frequency of Guerrilla-heavy rainfall is increasing, so it is quite important to predict heavy rainfall even within a few minutes. Nakakita et al. (2016) discovered the large vertical vorticity inside the baby cell aloft is useful to predict the Guerrilla-heavy rainfall, and also discovered the baby cells have vertical vortex tubes. By these results, we considered that the horizontal vortex tubes were caused by vertical shear of horizontal wind and these were tilted into vertical by an updraft. This hypothesis is popular in large scaled clouds, but it is not unclear in small scaled clouds. This paper shows two findings. One is that the strongest updraft exists between positive and negative vorticity using high ZDR column and multi Doppler technique. The other is that Guerrilla-heavy rainfall is caused by not so strong vertical shear as liner convective system. These unlock the developing process of small scaled cumulonimbus cloud