冷涡背景下一次致灾超级单体雹暴过程的数值模拟

A Numerical Simulation Study of a Supercell Hailstorm under a Cold Vortex

利用WRF模式,结合自动站观测资料、多普勒雷达资料和NECP再分析资料,对2018年6月13日山东中部一次冰雹天气过程的环流背景、触发和维持机制、雹云流场结构特征以及冰雹形成机制进行分析。结果表明:本次冰雹天气过程是在华北冷涡背景下,由中尺度地面辐合线触发生成的超级单体雹暴过程。降雨和下沉气流引发的地面冷池进一步增强了地面辐合;雹云顶端强辐散出流的抽吸作用是动力不稳定维持机制。WRF模式模拟的雹云具有有界弱回波、回波悬垂等超级单体特征。模拟雹云的成熟阶段0℃高度位于4km,超过40dBz的回波高度达到12km;在流场上主体为上升运动,且上升运动两侧存在上升→下沉→上升运动的转换,有利于冰雹的碰并增长。雪晶最初由过冷云水和云冰碰并生成,之后通过碰并过冷水转化为霰粒子,为冰雹生成提供了充足的雹胚。霰粒子和雹粒子在上升运动的带动下反复经过雹云中的过冷水累积带有利于自身不断增长并转化形成大冰雹。

Based on the automatic meteorological station data,Doppler radar data and NECP/FNL reanalysis data,the circulation background,trigger and maintenance mechanisms,supercell structure,and cloud microphysical characters of a supercell hailstorm occurred on 13 June 2018 in the central Shandong Province are studied with the WRF model.The study shows that the hailstorm was a supercell hailstorm triggered by the mesoscale convergence line under the background of cold vortex in North China.The suction of the strong divergent flow at the top of the hail cloud was the dynamic instability maintenance mechanism.In the mature stage of the simulated hail cloud,the height of the 0℃level was 4 km,and the echo height of more than 40 dBz reached 12 km;in the flow field,ascending motion was dominated,and there was a motion conversion of ascending-descending-ascending on both sides of the ascending motion,which was conducive to the collision and growth of the hail.The snow crystals were formed by the collision of supercooled cloud water and cloud ice at first,and then transformed into graupel particles by the collision of supercooled water and cloud ice,which provided enough hail embryos for hail formation.Graupel and hail particles,driven by the ascending motion,passed through the supercooled water accumulation zone of the hail cloud repeatedly,which was conducive to their continuous growth and transformation into large hailstones.