Formation mechanism of a multi-stage severe convective weather event accompanied by local tornado in Henan

Henan encountered a multi-stage severe convective weather event (hereinafter referred to as "6.13" event) accompanied by local tornado on 13 June 2022. Using conventional observation data, regional automatic weather station data, satellite cloud images, Doppler weather radar data, ERA5 reanalysis data and other relevant data, we conducted an analysis on atmospheric circulation environment and the evolution characteristics of mesoscale systems for the "6.13" event. In addition, we discussed the initiation and maintenance mechanisms of convection in the different periods of this event and the radar characteristics of the local tornado in Puyang of Henan. Results are as follows. (1) The "6.13" event occurs under the northwest airflow behind the northeast cold vortex trough, and it is characterized by wide impact range, long duration and multiple types of disaster weather. (2) Radar detection results show that the severe convective systems in the "6.13" event passed through Henan in three periods one after another, and strong echoes in each period lasts for 8-9 hours, with the moving speed of 30-50 km·h-1. Most of the severe convective systems are multi-cells that all moved from northwest to southeast, with some of their areas overlapping under the guidance of northwest airflow. (3) Maintenance of the strong conditional instability and the moderate to strong vertical wind shear over Henan is an important cause for multi-stage severe convective weather in the "6.13" event lasting for a long time. The first period of local severe convection in Henan is mainly triggered by the convergence line or convergence center in the boundary layer formed by the combined effect of daily changes of wind field, local cold air activity, topographic distribution, while the second and third periods of severe convection are triggered by the gust front or outflow boundary accompanied by the surface mesoscale thunderstorm high formed by the strong developing convection systems in the surrounding area in the previous period or the same period. (4) The local tornado in Puyang is generated by a rapidly developing supercell storm. The hook echo and mesoscale cyclonic vortex appear 12 minutes after this supercell storm, and the tornado vortex characteristics (TVS) appear 18 minutes later. The hook echo and mesoscale cyclonic vortex are 6 minutes ahead of the occurrence of tornado, which can provide a reference information for early warning local tornadoes.