Differences in tornado activities and key tornadic environments between China and the United States

Abstract

AbstractThe yearly tornado occurrence in China is approximately 5–10% of that in the United States, and the peak month of tornado occurrence in China is July, while that in the United States is May. However, the two countries have nearly the same land area and similar latitudinal location. This study attempts to disclose the differences in the key tornadic environments that are most possibly responsible for the large discrepancy of tornado occurrences observed between the two countries. The region with the highest tornado density in China (JS) is compared with three similarly sized regions in the United States, including two tornado‐prone regions (UC and USE1) and one region similar to JS (USE2). The results show that JS has a much lower tornado frequency than UC and USE1, mainly due to JS's much lower likelihood of multiple tornadoes occurring in a short period during its tornado season. Compared with UC and USE1, JS features relatively low mean values of the significant tornado parameter (STP) during their respective tornado seasons. The STP, incorporating several tornado‐related variables, was found to show a monotonic relationship with the total tornado count at a seasonal scale and perform well to explain monthly variations in tornado frequencies. Compared with the target regions in the United States, JS has a similar magnitude and decreasing trend of the 0–6‐km vertical wind shear from spring to summer, but a later increase in instability. Resulting from a balance between the decreasing vertical shear and the increasing thermodynamic instability, JS features a delayed monthly peak of STP and thus a delayed tornado season, which makes JS having a worse kinematic environment for tornadogenesis with far lower low‐level vertical wind shear during its tornado season than that of the United States.