Multiple Doppler analysis of the Tsukuba tornado on May 6, 2012 - A supercell tornado in convergence line

On March 6, 2012, four tornadoes occurred around Kanto-area, Japan. The number of casualties by the tornadoes was 59 and 978 houses were completely or partially destroyed. The Tsukuba tornado, the strongest of the four, was rated at F3 by the Japan Meteorological Agency (JMA) and the other tornadoes were rated at F0-F2.

Yamauchi et al. (2012) observed the tornado by the Meteorological Research Institute (MRI) C-band polarimetric radar at close range (about 15 km). They showed that a mesocyclone signature was detected in the parent storm of the tornado and the observed characteristics of polarimetric parameters such as differential reflectivity (Zdr) and correlation coefficient (Rhohv) were consistent with those of tornadoes in Ryzhkov et al. (2005).

The detected mesocyclone and the characteristics of polarimetric parameters suggest that the parent storm of the tornado was a supercell. Surface analysis showed that the supercell was collocated with a pre-existing convergence line passed rapidly around Kanto-area at that time. In Kanto-area, such supercell tornadoes collocated with pre-existing convergence line/zone were reported (e.g., Suzuki et al., 2000), but the details of the tornadogenesis remain unknown. We are speculating that the convergence line played an important role in tornadogenesis of the Tsukuba tornado. In order to clarify the tornadogenesis, multiple Doppler analysis with a dense network of radars was conducted.