青岛市一次局地大暴雨天气成因和逆风区特征分析

利用地面和探空气象观测数据、雷达探测资料以及ECMWF（ERA5）0.25°×0.25°全球再分析数据，分析了2016年8月19日青岛市环胶州湾一次局地大暴雨过程的环流形势、环境条件及逆风区演变特征。结果表明：副热带高压边缘的地面冷锋进入倒槽，冷空气向地面辐合线的暖区渗透触发对流天气是此次过程的形成机制。此次大暴雨过程与地形关系紧密，主要分布在低层暖湿气流和山脉抬升作用形成的迎风坡前位涡大值区，该区域中低空垂直上升运动和相对湿度配合较好。大暴雨区站点的强降水时段与垂直上升运动时段吻合，小时最大雨量出现在垂直上升运动强度的跃增阶段。过程降水开始前，0℃层高度和近地面层比湿变化不大，CAPE值、K指数以及垂直风切变等各项不稳定指数均较08时明显增强。雷达产品分析显示，造成大暴雨的对流单体呈暖区对流特征，强降水前20~30min垂直风切变增强。此次降水过程产生的4处逆风区均出现在对流单体生成之后，为对流单体下沉气流产生的与环境风相反方向的辐散气流。其中2处低层相对湿度大值区的逆风区能得到发展增强，而逆风区的发展则进一步促进了对流增强，此演变特征对本次大暴雨过程的临近预报预警有较好的指示作用。

Analysis for the Causes and the Characteristics of Upwind Area of a Local Heavy Rainstorm in Qingdao

Based on surface and sounding data, radar data and ECMWF (ERA5) 0.25°×0.25° global reanalysis data, the circulation situation, environmental conditions, radar products and the evolution characteristics of headwind area during a local heavy rainstorm were analyzed, which happened in Jiaozhou Bay, Qingdao City on August 19, 2016. The results show that surface cold front at the edge of the subtropical high entering the inverted trough, and the convective weather triggered by the infiltration of cold air into the warm area of the surface convergence line was the formation mechanism of this process. The heavy rainstorm process was closely related to the topography, and it mainly distributed in the large value area of the front vortex of the windward slope formed by the low altitude warm and humid air flow and mountain uplift, and the vertical ascending motion in the middle and low levels and relative humidity in this area are well coordinated. The period of heavy precipitation in the heavy rainstorm area was consistent with the period of vertical ascending motion, and the maximum hourly rainfall appeared in the jump stage of vertical ascending motion intensity. The height of 0℃ layer and the specific humidity of the near surface layer had little change before the beginning of precipitation, while the instability indexes of CAPE, K index and vertical wind shear were significantly enhanced compared with 8.a.m. The analysis of radar products showed that the convective cells causing the heavy rainfall were convective storms in the warm zone, and the vertical wind shear increased 20~30 minutes before the heavy rainfall. The four headwind areas generated during the precipitation process all appeared after the formation of the convective cells, which were the divergent airflow generated by the downdraft of the convective cells in the opposite direction to the ambient wind. Among them, the upwind area of the two low-level relative humidity areas with large value can be developed and enhanced, while the development of the upwind area further promoted the enhancement of convection. This evolution feature has a good indicator function for the near forecast and early warning of the heavy rain process.