A Comparison between the Only Two Documented Tornado Outbreak Events in China: Tropical Cyclone vs. Extratropical Cyclone Environments

This study documents the features of tornadoes, their parent storms and the environments of the only two documented tornado outbreak events in China. The two events were associated with tropical cyclone (TC) Yagi on 12 August 2018, with 11 tornadoes, and with an extratropical cyclone (EC) on 11 July 2021 (EC 711), with 13 tornadoes. Most tornadoes in TC Yagi were spawned from discrete mini-supercells, while a majority of tornadoes in EC 711 were produced from supercells imbedded in QLCSs or cloud clusters. In both events, the high-tornado-density area was better collocated with K index rather than MLCAPE, and with entraining rather than non-entraining parameters possibly due to their sensitivity to mid-level moisture. EC 711 had a larger displacement between maximum entraining CAPE and vertical wind shear than TC Yagi, with the maximum entraining CAPE better collocated with the high-tornado-density area than vertical wind shear. Relative to TC Yagi, EC 711 had stronger entraining CAPE, 0–1-km storm relative helicity, 0–6-km vertical wind shear, and composite parameters such as entraining significant tornado parameter, which caused its generally stronger tornado vortex signatures (TVSs) and mesocyclones with a larger diameter and longer lifespan. No significant differences were found in composite parameter of these two events from U.S. statistics. Although obvious dry air intrusions were observed in both events, no apparent impact was observed on the potential of tornado outbreak in EC 711. In TC Yagi, however, the dry air intrusion may have helped tornado outbreak due to cloudiness erosion and thus increase in surface temperature and low-level lapse rate.