青岛机场一次冰雹过程的双偏振雷达分析

Dual-Polarization Radar Analysis of a Hail Process at Qingdao Airport

摘要:

利用常规气象观测站点资料、探空资料、青岛S波段多普勒和双偏振雷达资料对2023年7月8日下午青岛机场一次对流单体冰雹过程天气背景以及雷达回波特征进行分析。结果表明：此次冰雹过程是在500 hPa强西风带、冷涡槽的共同作用下发生的，具有很强的局地性。整层大气具有强的不稳定性，上干下湿特征明显，低层垂直风切变强度中等，深层垂直风切变较强，0～6 km风矢量差达到21 m/s，高低空温差较大，湿球温度0 ℃高度为4 km。雷达回波具有高耸的强回波、有界弱回波区、回波悬垂和三体散射结构，同时中层4～8 km的高度处有明显中气旋结构，气旋直径约4 km，辐合层厚度约为3.2 km，高层出现速度辐散，这些均为典型雹暴的雷达特征。单体的垂直液态水含量(C-VIL)和垂直液态水含量(VIL)密度的大值能够很好对应冰雹粒子，C-VIL突变还能作为预报冰雹和大风参考指标，C-VIL跃增出现比青岛机场降雹提前30 min，骤降出现比青岛机场大风出现提前7 min。这次冰雹过程，双偏振雷达差分反射率因子Z_DR和相关系数ρ_hv能有效区分冰雹和强降水，而差分相位常数K_DP大值区对应大雨或融化的冰雹，需要结合其他参量进一步判断粒子形态。这次冰雹过程出现了明显的Z_DR和K_DP柱结构，Z_DR柱高于K_DP柱，Z_DR柱对应较强的上升运动，与速度图上的中气旋位置相对应，K_DP柱对应着较明显的下沉气流。分析的结果能为青岛机场的冰雹短临预报提供一定的参考，也对于实际应用双偏振雷达产品有一定的指示意义。

Abstract:

Using the data from conventional meteorological observation stations, sounding data, and S-band Doppler and dual-polarization radar data from Qingdao, the weather background and radar echo characteristics of a convective hail event at Qingdao Airport on the afternoon of July 8, 2023 are analyzed. The results show that the hail event occurred under the combined action of a strong westerly wind belt at 500 hPa and a cold vortex trough, with strong local characteristics. The entire atmosphere had strong instability, with obvious characteristics of dryness in the upper layer and wetness in the lower layer. The vertical wind shear intensity in the lower layer was moderate, while the vertical wind shear intensity in the deep layer was strong. The wind vector difference between 0 and 6 km reached 21 m/s, and the temperature difference between high and low altitudes was large. The height at wet bulb temperature 0 ℃ was 4 km. The radar echoes had high-rise strong echoes, bounded weak echo areas, echo hangings, and three-body scattering structures. At the same time, there was a clear mesocyclone structure at an altitude of 4-8 km in the middle layer, with a diameter of about 4 km and a thickness of about 3.2 km in the convergence layer. There was a velocity divergence in the upper layer. These were all typical radar characteristics of hailstorms. The large values of C-VIL and VIL density could well correspond to hail particles, and the C-VIL mutation could also be used as a reference index for forecasting hail and strong winds. The C-VIL jump occurred 30 minutes before the hail at Qingdao Airport, and the sudden drop occurred 7 minutes before the strong wind at Qingdao Airport. During this hail process, the dual-polarisation radar parameters Z_DR and ρ_hv could effectively distinguish hail and strong precipitation, while the K_DP large value area corresponded to heavy rain or melted hail. It was necessary to combine other parameters to further determine the particle morphology. This hail process showed obvious Z_DR and K_DP column structures, with the Z_DR column higher than the K_DP column. The Z_DR column corresponded to strong upward motion, which corresponded to the location of the mesocyclone on the velocity diagram, while the K_DP column corresponded to a more obvious downdraft. The analysis results can provide some reference for short-term and imminent forecasts of hail at Qingdao Airport, and also have some instructive significance for the practical application of dual-polarisation radar products.