Analysis of extreme convective gusts caused by two types of weather storms during a strong convection event

Based on multi-source observational data, the extreme convective gale caused by two different types of storms during a severe convective process in Huang-Huai region on 30 April 2021 is discussed. Results indicate that the severe convective process occurred under the background of the Northeast Cold Vortex with strong vertical wind shear and stratification instability. The initial convective activities were triggered by a surface cyclone and associated front and developed rapidly. The convective systems went through different evolution stages such as organization, movement, initiation and explosive development of isolated storm cells, and merge and reorganization in the subsequent 10 hours of propagation process, during which different characteristics of convective winds were caused by two different types of storms. Represented by Huai'an station, extreme convective winds (36.2 m/s) occurred in central Jiangsu due to the downburst caused by a strong supercell storm. An obvious hook echo structure occurred in the lower layer of the storm, corresponding to the deep mesocyclone with strong cyclonic rotation. As the extreme wind occurred, the mesocyclone stretched upward and downward simultaneously, accompanied by a horizontal rapid contraction process. The downdraft throughout the whole storm was located at the back of the hook structure of the storm, and the strong downdraft diverged outward rapidly near the ground, accompanied by a rapid drop of the strong reflectivity core in the storm. This resulted in extreme winds on small spatial-temporal scale and significantly discontinuous spatial distribution in Huai'an. Represented by Nantong area, the development of extreme winds in southeastern Jingsu involved interactions between multi-scale weather systems. An obvious gust front developed at the front of the linear convective system, resulting in large area of surface gales above Grade 10. The extreme gale in Tongzhou bay of Nantong (47.9 m/s) occurred at the back of the gust front, which was caused by the superposition effect of multi-scale systems, including the strong cold pool induced by the linear convective storm and the surface cold front, the rapid development of the surface cyclone that entered the sea and the downdraft in the rear of the storm with downward transfer of upper wind momentum.