Climatic characteristics and environmental conditions of tornadoes in Liaoning under the background of cold vortex

In order to study the relationship between cold vortex and tornado in Liaoning, the characteristics of tornado occurrence in Liaoning under the background of cold vortex are investigated. Using tornado observations and weather disasters data in Liaoning province and the ERA5 atmospheric reanalysis data of the European Center for Mediumrange Weather Forecasts (ECMWF) from 1951 to 2020, tornado cases in Liaoning under the cold vortex background are collected and sorted out. Differences between the physical parameters of EF2—4 (EF2+) and EF0—1 (EF1−) tornadoes under the cold vortex background are compared. The results are as follows. (1) Tornadoes under the cold vortex background mainly occur in the coastal area and the central and northern plain of Liaoning province. The average distance between the tornado and the center of the cold vortex is nearly 900 km. The stronger the cold vortex, the farther its center is from the tornado; the weaker the cold vortex, the closer the distance between the center of the cold vortex and the tornado. Under the background of cold vortex, tornadoes in Liaoning province mainly occur between the southeast and southwest quadrants of the cold vortex, and frequently occur in the enhancement stage of the cold vortex. (2) The number of tornados in Liaoning province in the cold vortex background accounts for nearly 50% of the total samples from 1951 to 2020, and the number of tornados is positively correlated with the number of cold vortex days. The distance between the mean location of the tornadoes in Liaoning under the background of the cold vortex and the average center of the cold vortexes has obvious monthly changes with the closest distance in August. (3) Comparing EF2—4 (EF2+) with EF0—1 (EF1−) tornadoes under the background of cold vortex, the thermal and dynamic environmental parameters of EF2+ tornadoes are 40% and 65% higher than that of EF1− tornadoes. Comparing the tornadoes in Liaoning under the background of cold vortex and tropical cyclone tornadoes, it is found that the convective available potential energy of the cold vortex tornadoes is about 3 times that of the tropical cyclone tornadoes, but the storm relative helicity of the cold vortex tornadoes is only half that of the tropical cyclone tornado. (4) Energy helicity index (EHI) and Significant tornado parameter (STP) can be used to determine the tornado level in Liaoning under the cold vortex background, which is far below the comprehensive parameter threshold of the American tornado. Therefore, the intensity and position of the cold vortex are closely related to the occurrence of tornado in Liaoning. The physical quantity parameters of the EF2+ tornado under the cold vortex background are significantly greater than those of the EF1− tornado. The thermal and dynamic environmental parameters of tornado in Liaoning under the background of cold vortex and tropical cyclone tornado are quite different. Adjusting the Energy helicity index and Significant tornado parameter thresholds can improve the POD of strong tornado in Liaoning under the background of cold vortex.