Abstract:

A series of tornado weather processes that occurred in northern Liaoning province on June 1, 2023 were diagnosed using the data from intensive automatic stations, FY-3G low-orbit meteorological satellites, Doppler radar and historical data. The results show that the northeastern cold vortex provides dry and cold conditions in the upper levels, and the southerly air flow in the front of the surface cyclone transports warm and humid air to the north, forming a strong convective instability in northern Liaoning province. In the lower levels, there is a nearly vertically distributed frontal zone. The high positive vorticity at the 950~750 hPa in front of the frontal zone is well matched with the vertical velocity, and the dynamic uplift effect is enhanced, which is conducive to the development of the convective system. The dry lines, large temperature gradient zones and cold pools associated with the mesoscale frontal areas lead to the formation of linear convective cloud belts in western Liaoning province. Local small-scale vortices may be the dynamic trigger system for the tornado in Fuxin. The density flow generated between the strong cold pool in northern Liaoning province and the strong warm ridge in the southeast caused the local westerly wind to increase on the east side of the cold pool. The superposition effect of the wind speed and direction convergence along with the strong cold pool may be the reason for the triggering of the tornado in Kaiyuan. Under the background of the northeastern cold vortex and the special coastal and mountainous terrain, northern Liaoning province has the convective potential conditions for tornadoes. Fuxin is located in the special terrain of an inverted "U" shape with high altitude in the surrounding area and low in the middle. It is easier to form small-scale cyclonic closed circulation, which may be one of the reasons why Fuxin is the center of the Liaoning province tornado.

Key words: Tornadoes, Circulation patter, Environmental condition, Small-scale and mesoscale feature