Synoptic Characteristics of the Japan Tsukuba Tornado

In this study, we conducted synoptic and mesoscale analyses to study the cause of the Japan Tsukuba tornado development, which occurred on 0340 UTC 6 May 2012. We analyzed surface and upper-level weather charts, thermodynamic diagram with hodograph and stability indices, moisture flux, SREH, isentropic analysis, PV, and Froude number. Prior to the tornado event, there was a circular jet stream over Japan and the surface was moist due to overnight precipitation. Circular jet stream brought cold and dry air to the upper-level and sky clearing with strong solar radiation heating the ground. A tornadic supercell developed in an area that was potentially unstable. Sounding data at Tateno showed a capping inversion at 900hPa on 0000 UTC 06 May. Strong insolation in the early morning hours and removal of the capping inversion instigated vigorous updraft with rotation due to vertical shear in the upper-level. This caused multiple tornadoes to occur from 0220 to 0340 UTC 6 May 2012. When comparing Tateno’s climatological temperature and dew-point temperature profile with that of the day of tornado, the mid-level was more moist than typical tornado sounding. This study shows that Tsukuba tornado development is due to a combination of a) topography and PV anomaly, which increased vorticity over the Kanto Plain; b) vertical shear, which produced horizontal vortex line; and c) thermal instability, which triggered supercell and tilted the vortex line in the vertical.