基于多源资料的乌鲁木齐市两次极端短时强降水对比分析

Comparative Analysis on the Two Extreme Short-time Heavy Precipitation in Urumqi Based on the Multi-sources Data

利用常规观测、区域自动站、FY-2G气象卫星、多普勒雷达、风廓线雷达及NCEP 1°×1°再分析等多源资料,分析乌鲁木齐2015年6月9日和27日(分别简称“6·09”和“6·27”过程)两次极端短时强降水成因。结果表明:(1)“6·09”过程是在高压脊前西北气流下,由700、850 hPa双低空急流耦合触发,配合强低层风切变,低层水汽快速聚集造成的局地性强对流天气,TBB最低为-52℃,雷达回波为典型的“列车效应”,强回波达55 dBZ。“6·27”过程是在中亚低涡背景下,西南、偏西、偏东三条水汽路径使得整层增湿,配合持续时间较长的弱低层风切变,是系统性降水中的强对流天气,TBB最低为-44℃,雷达回波为混合性降水回波中分散的对流单体,强回波达50 dBZ;此外,“6·09”过程热力不稳定条件较好。(2)风廓线雷达显示两次过程低层均存在垂直风切变,折射率结构常数C_(n)^(2)均在强降水时迅速增大并维持高值,随着降水减弱迅速减小;两次过程均发生在中β尺度对流云团TBB梯度最大处。(3)雷达回波均属于低质心对流风暴,且地面均配合有中γ尺度气旋性风场辐合或切变。

The causes of the two extreme short-time heavy precipitation in Urumqi on June 9th and June 27th,2015(“6·09”and“6·27”in short)were analyzed based on the data from conventional weather stations,regional automatic weather stations,FY-2G satellite,Doppler radar,wind profile radar,and NCEP1°×1°reanalysis data.The results indicated that:(1)The“6·09”(“6·27”)event was local convective precipitation(convective precipitation in a synoptic process),which took place in the northwest airstream ahead a pressure ridge(Central Asian vortex),triggered by the coupling of 700 hPa and 850 hPa double low-level jets,combined with strong(weak and long duration)low-level wind shear,and rapid accumulation of low-level vapor(humidifying by three water vapor paths in the southwest,west,and east).Besides,the minimum of TBB was-52℃(-44℃),with the radar echo characterized as“train effect”(scattered convective cell developed in cumulus-stratus)and the maximal radar reflectivity factor of 55 dBZ(50 dBZ).The thermal instability of the“6·09”process was better.(2)The wind profiler radar showed that there was vertical wind shear in the lower layers of the two processes,and the refractive index structure constant C_(n)^(2) increased rapidly and maintained a high value during heavy precipitation,and decreased rapidly as the precipitation weakened;both two occurred where the TBB gradient of the meso-β-scale convective cloud cluster is the largest.(3)Both were low-centroid convective storms,and concurrent with the convergence of wind shear line or the meso-γ-scale cyclonic wind field.