Abstract:Based on the data of dual polarization Doppler radar, wind-profiling radar, disdrometer, dual-Doppler radar retrieval, automatic weather stations and FNL reanalysis data, this paper analyzes the mesoscale characteristics of warm-sector torrential rain in southeastern coast of Fujian Province on 7 May 2018. The results show that this torrential rain process occurred inside the strong ultra-low-level southwest jet. The pulsation feature of ultra-low-level jet was obvious. Sudden enhancement of the jet favored the low-level disturbance, which caused significant low-level convergence. Deep southwest jet led to high consistency of convective echo pattern and echo moving direction, causing multiple severe convective systems to pass the same area repeatedly (a train effect), which was an important reason for the severe rainfall to last such a long time. There existed both wind speed and direction convergence inside the strong echo in horizontal direction. In vertical direction, there was significant wave-like motion in the echo band with the ascending motion in the front of the strong echo. This could guide echo to move northeastward. At the same time, there was significant compensatory secondary circulation in 〖JP2〗southeast of the strong echo, maintaining low-level convergence and the upstream.〖JP〗 In addition, high concentration of small raindrops with a few large raindrops was the main cloud microphysical characteristics of this warm-sector torrential rain.