Multi-Radar Observation of Tornadogenesis in a Shallow Supercell of Typhoon Hagibis (2019)

Abstract:

The purpose of this study is to elucidate generation processes of a tornado associated with Typhoon Hagibis (2019) observed by an X-band phased array weather radar (PAWR) and nearby C-band dual-polarization weather radars. By focusing on a ~10-min period around the time of passage over the damage area ranked Japanese Enhanced Fujita (JEF) scale 2, we clarified finely-resolved radar signatures of tornadogenesis based primarily on the analysis of PAWR data. About five minutes before producing JEF-2 damage, a counter-rotating vortex pair appeared above rear-flank out flow region. The vortex pair developed upward and its counterclockwise vortex approached preexisting mesocyclone located aloft. At their closest approach, an abrupt intensification of the counterclockwise vortex happened in the upper part and propagated downward. Meanwhile, significant vortex shrinking occurred at low levels. As a result, a small-scale tornadic vortex emerged over the damage area. We suggest that coupling of the vortex pair with mesocyclone and near-surface vorticity stretching played crucial roles in tornadogenesis. Since the coupling process occurred on a minute scale and was affected by subtle spatial change on a scale of hundreds of meters, the tornado occurred in highly sensitive conditions. In this presentation, we will also discuss the three-dimensional structure of tornadic debris signatures derived from the dual-polarization radar data in relation to the volumetric behavior of tornadic vortex.

Acknowledgement: This work was supported by JSPS KAKENHI Grant 17K13007 and 19K23466. In this analysis, we used PAWR data operated by Japan Radio Co., Ltd.