Analysis of the Tornadic Debris Signatures of the Ichihara Tornado in a Typhoon Environment Using Two Operational C-band Dual-Polarization Weather Radars

Abstract

The tornadic debris signatures (TDSs) of the Ichihara Tornado associated with Typhoon Hagibis (2019) were observed using two operational C-band dual-polarimetric weather radars and an X-band phased-array weather radar (PAWR). This TDS observation was the first to be made over Japan in a typhoon environment. The TDS bins spread over time, and the maximum vertical and aerial extents reached 2.4 km and 9.41 km², respectively. The estimated rise velocity of the TDS was 8 m s⁻¹. The first TDS was detected ∼1 min before damage reporting began. The TDSs became clearer along with the rotational velocity of the near-surface vortex detected by PAWR. The copolar correlation coefficient reached a minimum (0.27) ∼1 min after the tornado passed the most severely damaged area and increased gradually over 4 min. This suggests that heavy and/or dense debris was lofted and immediately fell out and/or diffused, whereas light debris remained aloft for ≥ 4 min. By comparing the PAWR-detected vortex signatures with aerial photographs, we inferred that the first TDS comprised vegetated debris, the clearest TDS mainly comprised destroyed manmade structures. These results indicate that TDS detection is effective both for investigating damage and for recognizing tornado's occurrence even in a typhoon environment.