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东北冷涡背景下弓形回波导致的雷暴大风成因分析

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

  • 摘要: 2022年6月25日傍晚辽宁省出现以雷暴大风为主的强对流天气,全省82个区域自动气象站出现8级以上雷暴大风,其中辽宁省北部的沈阳市马三家站阵风达13级(39.1 m·s-1),致灾严重。利用2022年6月25日17∶00—22∶00 (北京时)辽宁省1 668个区域自动气象站分钟级观测资料及常规探空、双偏振雷达、ERA5再分析等资料,对此次雷暴大风天气成因进行分析研究。结果表明:(1) 此次过程发生在东北冷涡背景下,辽宁处于冷涡西南象限,有利于冷涡西侧干冷空气与低层暖湿空气交汇。(2) 沈阳探空曲线呈低层暖干、中低层暖湿、中高层干冷的“X”型特征,且具有较强的垂直风切变,利于雷暴大风天气发生。(3) 此次过程雷达回波发展演变与经典弓形回波演变模型一致,初期孤立风暴导致局地大风,之后多单体风暴逐渐合并为弓形回波。在负浮力、动量下传和冷池密度流等共同作用下,沈阳城区出现大范围雷暴大风。(4) 弓形回波前沿存在浅薄的低空γ中尺度涡旋,低空涡旋旋转在近地面形成扰动低压导致下沉气流加强,涡旋与后侧入流急流共同作用导致雷暴大风出现。

     

    Abstract: 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.

     

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