对2024年7月19日杭州萧山机场一次低空风切变过程进行分析,发现此次低空风切变天气过程是由下游对流风暴后侧下击暴流的下沉辐散气流造成的。利用杭州萧山机场AWOS资料和浙江省自动气象站数据、多普勒天气雷达资料、风廓线雷达资料分析低空风切变过程中本场风向风速温度的演变特征、周边风场的演变、两次下击暴流演变情况及低空风切变高度和强度。分析表明:本次低空风切变受一股冷性偏东气流的影响,期间风向突转180˚,风速突然增大,温度呈非对称“V”型变化;本次低空风切变强度在水平风切变安全阈值之内,但其着陆顺风分量风速大于标准;冷性偏东气流是来自于嘉兴地区雷暴云下击暴流的下沉辐散气流,此辐散气流是先后由两个位置相近的雷暴云下沉气流叠加融合而成;第二次下击暴流比第一次下击暴流强度大且持续时间长,两次下击暴流都出现了反射率因子核的持续下降,对流层中层出现径向速度辐合,对流回波的后侧出现入流缺口,下击暴流出现在对流发展旺盛阶段之后;低空风切变主要位于400 m高度以下,风速变化小,表现为风向切变。The analysis of the low-level wind shear event at Hangzhou Xiaoshan Airport on July 19, 2024, revealed that it was caused by the descending divergent airflow from the rear of a downstream convective storm’s downburst. Using AWOS data from Hangzhou Xiaoshan Airport, automatic weather station data from Zhejiang Province, Doppler weather radar data, and wind profiler radar data, the evolution characteristics of local wind direction, wind speed, temperature, surrounding wind fields, and two downburst events were analyzed. The analysis showed that the low-level wind shear was influenced by a cold easterly airflow, with a sudden 180˚ wind direction change and increased wind speed. The intensity was within safe thresholds but exceeded standard landing tailwind speed. The wind speed increases suddenly and the temperature changes in an asymmetric “V” shape. The cold easterly airflow originated from the downburst in Jiaxing area, formed by merging downdrafts from two nearby thunderstorms. The intensity and duration of the second downburst is larger than that of the first downburst, and the reflectivity factor core of the two downbursts continues to decline, radial velocity convergence appears in the middle troposphere, inflow gap appears behind the convective echo, and the outflow of the downburst is now after the vigorous development of the convection. Low-level wind shear is mainly located below 400 m altitude, and the wind speed changes little, which is manifested as wind shear.
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