Environmental Conditions, Structures, and Mechanisms of Convective Storms of 2015 “Oriental Star” Capsizing Event and 2016 Funing EF4 Tornado

The “Oriental Star” capsizing event in 2015 (Hereafter 2015 event) and the Funing EF4 tornado event in 2016 (Hereafter 2016 event) are extremely rare damaging wind events caused by severe convective storms. Based on multi-source data, this paper applied the “ingredients-based” method to compare the atmospheric circulation backgrounds, environmental conditions, structure and mechanisms between these two events of convective storms. Results show that both these events occurred in partially similar circulation backgrounds, but there are considerable differences in the environmental conditions. For the 2015 event, the most important environmental conditions conducive to high surface winds are the significantly dry layer in the middle troposphere that makes a larger downdraft convective available potential energy, and 0-6 km vertical wind shear has only a medium intensity. For the 2016 event, all the environmental conditions are very favorable for mesocyclone tornado. The 2015 convective storm was a meso-β scale bow-shaped quasi-linear convective system with significant negative lightning flash, low mass center of reflectivity, and about 50 dBz of the maximum reflectivity. However, the 2016 convective storm was a meso-β scale classical supercell with significant positive lightning flash, high mass center of reflectivity, and about 65 dBz of the maximum reflectivity.There were multiple shallow downbursts in the low troposphere, and strong rear inflows and a mesovortex at about 5 km altitude in 2015 convective storm. Nevertheless, the 2016 supercell storm had a strong mesocyclone with base height less than 1 km and tilting northeastwards from bottom to top, and a tornadic vortex signature, and hook echo and overhang echo signatures; besides, it appeared rotating on the high-resolution visible images observed from geostationary meteorological satellites. The surface air temperature differences between the cold outflow of the 2016 supercell storm and the environment was less than 4℃, and they were weaker than those in 2015 event, therefore, not strong downdraft is one of the important mechanisms that produced a tornado in the 2016 event of supercell storm.