Lightning Characteristics of a Supercell Thunderstorm Observed by Tokyo LMA, X-Band Polarimetric Radars, and an X-Band Phased Array Weather Radar in Tokyo, Japan

On 19th August 2017, a supercell thunderstorm was observed in Tokyo Metropolitan area by Tokyo LMA and X-band polarimetric radars, and an X-band phased array weather radar (PAWR). In this study, development process and lightning characteristics of the supercell thunderstorm were investigated. The first echo of the thunderstorm was detected by an X-band polarimetric radar located in Ebina city at 15:05 JST (JST = UTC + 9hr) near the border between Tokyo prefecture and Saitama one. The echo top height and the number of lightning radiation sources started increasing at 16:05 JST abruptly. The echo top height was over 18 km at 17:15 JST, which means that the echo top height exceeded the tropopause (tropopause height was about 16 km). In the mature stage of the thunderstorm, overhanging echo structure (vault) and lightning hole were observed between 17:00 and 17:30 JST intermittently.

We investigated the relationship between spatial distribution of lightning radiation sources and fine scale internal structure of the thunderstorm during the developing stage and dissipating stage of the storm using the data of the PAWR and the Tokyo LMA. The PAWR has not only high temporal resolution but also high spatial resolution. We used the CAPPI data of the PAWR with a volume scan of 30-second cycle and spatial resolution of 250 m for the analysis. New convections generated and developed in the western part of the thunderstorm continuously. Most of lightning radiation sources were observed in the western part of the thunderstorm. The high-density core of lightning radiation sources were elevated from 10 km to 15 km in height for about ten minutes in the western part of the storm. The ascent of the high-density cores of lightning radiation sources were observed more than ten times for about one and half hours in the thunderstorm and was associated with the increase of the echo top height of new convection which generated in the western part of the thunderstorm.