Abstract:
Using data from ERA5 reanalysis, lightning locators, dual-polarization radars, and microwave radiometers, this study analyzed the environmental background, dynamic conditions, instability mechanisms, and characteristics of lightning and thunderstorm gale of an elevated severe thunderstorm in the northern Zhejiang region on November 28, 2022. The results are as follow. (1) this was an elevated convective event occurring ahead of a warm front, which was mainly influenced by the 500 hPa upper-level trough and low-level southwesterly jet stream. The vorticity advection increasing with height in front of the shortwave trough caused strong upward motion. The strong and deep convergence in the front of the low-level jet stream, and the strong vertical wind shear provided favorable dynamic conditions for the development of convection. (2) Mid-level dry air and strong downdraft convective available potential energy (DCAPE) contributed to the formation of intense downdrafts. The joint action of conditional instability and conditional symmetry instability provided sufficient energy conditions for the development of convection, among which conditional instability played a major role. (3) Dual-polarization radar data analysis showed that, during the peak stage, the 50 dBz strong echoes reached the −20 ℃ layer, and above the 0 ℃ layer,
ZDR columns and
KDP columns existed. The coexistence of strong updrafts and a large number of graupel particles was conducive to the frequent occurrence of lightning. (4) With the rapid descending of the reflectivity core, the rear inflow jet formed and dropped to the surface through the reflectivity core of the storm, indicating that the strong downdraft generated by convection could penetrate through the inversion layer and bring the high momentum air to the ground. Little changes in the ground temperature were observed before and after the convection, indicating that the negative buoyancy effect of the downdraft at low levels was small. The equivalent hydrometeor load estimation showed that the drag effect of large particles, like hail, could have a strong enhancement effect on the downdrafts.