Analysis of the causes of thunderstorm winds caused by bow echoes under the background of Northeast China cold vortex

Strong convective weather dominated by thunderstorm strong winds appeared in Liaoning Province in the evening of 25th June 2022. Eighty-two automatic weather stations across the province recorded thunderstorm strong winds of magnitude 8 or above. Among them, the Ma Sanjia Station in the northern part of Shenyang City, Liaoning Province, recorded wind speeds of 13 on the Beaufort scale (39.1 m·s-1), resulting in severe damage. By utilizing the minute-level observational data from automatic weather stations in Liaoning Province on June 25 from 17:00 BT to 22:00 BT, as well as conventional radiosonde, dual-polarization radar, and data from the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis, an analysis and study were conducted on the formation mechanism of this thunderstorm strong wind event. The results are as follows. (1) Liaoning is located at the southwest quadrant of the northeast cold vortex, where the cold dry air on the western side of the vortex converged with warm moist air in the northern part of Liaoning Province on the evening of the 25th. (2) The Shenyang sounding curve exhibits a low-level warm and dry layer, a mid-low-level moist layer, and a mid-high-level dry and cold layer with an "X" shaped pattern. Additionally, it features strong vertical wind shear, which creates favorable conditions for the occurrence of severe convective weather. (3) The evolution of radar echoes in this process is consistent with the evolution of classic bow echoes; isolated thunderstorms in the initial stage lead to locally strong winds. Subsequently, multiple individual storms gradually merge into a bow echo. The interaction of negative buoyancy, momentum transport, and cold pool density currents collectively results in widespread thunderstorm winds in the Shenyang urban area. (4) Along the leading edge of the bow echo, shallow low-level gamma scale cyclones are present. The rotation of low-level cyclones forms perturbation low pressure near the ground, enhancing the downdraft, while the cyclones interact with the strong inflow jet on the rear side, leading to locally strong thunderstorm winds.