Abstract:Based on conventional observation data, frequently observed data of automatic weather station, Doppler weather radar data and ERA5 reanalysis data, the mesoscale causes for a rarely-seen extreme thunderstorm gale in the central part of Jilin Province on the morning of 9 September 2021 is analyzed. The results show that the squall line system that produced thunderstorm was formed by the deep northeast cold vortex and the large-scale frontogenesis at the tail of the cold front. The strong dry air in middle layer and the temperature lapse rate closed to dry adiabatic below the inversion layer were conducive to the generation of extreme thunderstorm gale. The existence of dry and warm cover led to rapid enhancement of low-level warm and humid air, and the CAPE value surpassed 1600 J·kg-1 at the nearing moment, which made the stratification become extremely unstable in a short period of time. The average wind speed in the entrainment layer was above 20 m·s-1, and the downward transfer of momentum was beneficial to the enhancement of ground wind speed. The extreme thunderstorm gale occurred near the meso-γ scale vortex in the tail front of squall line after fracture, but the causes for the extreme thunderstorm gale at the two stations near the vortex were obviously different, of which the thunderstorm gale at Nongda Station occurred when the air pressure dropped sharply, the temperature rose sharply and the minute precipitation was weak. Thus, it was caused by the strong sinking divergent airflow (cold pool outflow) in front of the squall line accelerating into the vortex under the action of strong southerly airflow, and the convergence updraft was rapidly enhanced. It was significantly different from the extreme thunderstorm gale caused by the strong sinking divergent airflow formed by the drag of precipitation particles at the nearby Nongboyuan Station and Changchun Station.