Peculiar Supercell Tornadoes caused by Typhoon ‘Neogri'

Two tornadoes simulataneously occurred near Kochi airport when the outer rainband of Typhoon 'Neogri' passed through the Kochi Plain at about 6:00 JST on 10 July, 2014. The present analytical study aims to clarify the charcteristics of their parent storm by using data of the JMA radar and our polarimetric radars in Kochi University. When the first mesocyclone appeared at 5:31 JST on 10 July, the parent storm had some features of mini supercell; i.e., weak echo region, hook echo and vault. But, the arrangement of hook echo is quite different from that of ordinary supercell. The present storm was maintained by the strong rear inflow conversing to the outer rainband. Figure 1 shows the Schmatic diagram of this situation. The parent storm has been moved to northeast in the outer rainband at 27 m/s. The rear inflow was strong southwestely wind of 38 m/s in Doppler velocity converging to the outer rainband. Therefore, the parent storm was the mini supercell having unique airflow structure maintained by the rear inflow. After the second mesocyclone appeared at 5:41 JST, the diameter of mesocyclones became rapidlly smaller and the strong rear inflow got weak until 5:45 JST. When the parent storm landed at 6:21 JST, the weak rotating flow of the first mesocyclone still lived but vault was disappeared and diverging flow was observed under the mesocyclone. The gust front was formed at the south edge of the parent storm. However it was different from the rear flank and forward flank gust fronts of ordinary supercell. Then, the parent storm decayed and lost the feature of supercell as the rear inflow became weak. The west tornado was born under the first mesocyclone and the east tornado appeared under the second mesocyclone. These tornadoes survived until landfall of the parent storm though it became weak. These tornadoes were maintained under the cyclonic wind shear in the outer rainband.