Statistical analysis of atmospheric vortexes affecting Zhejiang and causing regional rainstorms nearly 43 years

Based on the reanalysis data from the National Centers for Environmental Prediction Climate Forecast System Reanalysis and historical precipitation data from Zhejiang Province, characteristics of vortexes that have affected Zhejiang and induced regional heavy rainstorms over the past 43 years are statistically analyzed with the objective identification and tracking algorithm. The results are as follows. Firstly, low vortexes affecting Zhejiang are mainly located in the middle and east of Anhui, the northeast of Jiangxi, and the middle and south of Jiangsu. They are usually active from April to June, with the highest frequency in June. Vortexes from night to early morning are more likely to affect Zhejiang, and cause regional heavy rainstorms, but the lifetime of these rainstorms tends to be short. Secondly, the statistical characteristics of vortexes inducing rainstorms in Zhejiang are similar to those affecting Zhejiang. The low vortexes are most likely to cause regional rainstorms in summer (June to August). Thirdly, when vortexes cause regional rainstorms, Zhejiang is usually located in front of the upper shallow trough, and the low-level high-energy region. Affected by the warm shear line on the east side of the vortexes, the southwest warm and wet airflow from the South China Sea continuously transports water vapor to Zhejiang. Finally, in June during the Mei-yu season, the intensity of vortexes is strong, and the temperature meridian gradient and the southwest wind speed on the south side of vortexes are large. The regional rainstorm precipitation induced by vortexes is mainly located in the west of Zhejiang and is dominated by heavy rainfall. In August during the western Pacific subtropical high period, the regional rainstorm precipitation induced by the vortex is mainly in the southeast coastal area of Zhejiang, and characterized by scattered heavy rainfall.