Environmental Characteristics of Extratropical Cyclone Tornadoes in Liaoning

Abstract

Liaoning is one of the active regions for tornadoes in China, and the generation of a considerable number of tornadoes is associated with extratropical cyclones. In order to improve the understanding of environmental background and physical parameter characteristics, 42 extratropical cyclone tornadoes in Liaoning from 1979 to 2020 are statistically analyzed. The study is based on the reanalysis data of ERA5(ECMWF Reanalysis V5), combining with records of China Meteorological Disaster Classic and China Meteorological Disaster Yearbook. Results show that extratropical cyclone tornadoes are mainly distributed in the central and western Liaohe Plain and along the coast of the Bohai Bay. Significant tornadoes(EF2 and above) account for 28.6% of all extratropical cyclone tornadoes.Extratropical cyclone tornadoes occur mostly in the southwest and southeast quadrants of extratropical cyclones, corresponding to the warm area before the cold front. The high-value area of the storm relative helicity and convective available potential energy(CAPE) appear in the southwest-southeast quadrant of the extratropical cyclones, with a belt-like distribution. Extratropical cyclone tornadoes are mainly distributed within 1° of latitude in the northwest of the large-value area of storm relative helicity and the strong gradient area at the top of the large-value area of CAPE. The strong tornado parameter(STP) center is located near the -2° of longitude distance and -5° of latitude distance from the center of tornadic extratropical cyclones, and the maximum value is above 0.7. The large value area of STP corresponds to the high-incidence area of EF2 and above extratropical cyclone tornadoes. The cold front and dry line in the surface are the key trigger of extratropical cyclone tornadoes, and the induced tornadoes are mainly distributed near the warm ridge of temperature field and the top of the tongue of humidity field. Comparing the vertical distribution of humidity near the center of tornadic extratropical cyclones and the tail of the cold front, the strong cold pool caused by the strong high-level dry intrusion can generate excessively strong downdraft, which may be an unfavorable factor for tornado formation. Extratropical cyclone tornadoes are mostly distributed in the distributary area of the left air flow of the upper-level jet, corresponding to the strong upper-level divergence area. The large value area of 0-3 km vertical temperature lapse rate has a good correspondence with the high incidence area of weak tornadoes near the center of extratropical cyclones.

Keywords

• tornado
• extratropical cyclone
• environmental parameters