东北冷涡背景下沈阳地区一次强降水过程分析

利用辽宁省区域自动站、探空和多普勒雷达观测资料及ECMWF再分析资料, 对2016年6月30日发生在沈阳地区一次局地短时强降水过程的天气特征及可预报性进行分析。结果表明: 此次天气过程为东北冷涡背景下典型的午后强对流天气, 白天太阳辐射加热使得沈阳城区温度高于周边区域, 配合中低层的高湿环境具有较好的不稳定能量; 暴雨发生前2 h, 近地面至300 hPa高度西南气流不断增强, 低空急流出口区减压, 使得垂直运动增强, 上升运动高度达到对流层顶, 有利于触发和加强对流, 1.5—3.0 km的16 m·s^-1的西南风脉动和急流减弱消失对降水发生和结束有较好的指示意义; 午后低层辐合、高层辐散的不稳定层结在强降水发生前2 h建立, 散度最大时段与强降水时间对应较好; 雷达观测反映这次降水以低质心暖云降水为主导, 具有较高的降水效率, 地面辐合线触发了对流, 并逐渐发展演变成带状对流系统。从数值预报的结果来看, 模式未能报出城市下垫面对气象要素的影响, 对于地面辐合线的预报存在明显的滞后偏弱, 导致强降水预报难度增加。

Analysis of strong precipitation in the urban area of Shenyang under the Northeast Cold Vortex background

Using Liaoning province automatic station observational data, upper-air observation data, Doppler Radar data, and ECMWF reanalysis data, weather characteristics and predictability of the urban local short-term heavy rain process were analyzed under the background of cold vortex weather in Shenyang on June 30, 2016.The results show that the weather process is a typical afternoon strong convective weather.During the day, solar radiation heating results in the urban temperature higher than the surrounding areas and there is significant unstable energy in the middle and low-level with a high humidity environment.Southwest airflows from the ground to 300 hPa height have increased continuously since 2 hours before the rainstorm, meanwhile, the exit area of the low-level jet is depressurized, leading to intensifying the vertical movement and the ascending movement reaching the tropopause, which is beneficial to trigger and strengthen convection.Southwesterly wind pulsation and the weakening and disappearance of jets at heights from 1.5 km to 3.0 km and with the speed of 16 m·s^-1 have a good indication of the occurrence and end of precipitation.The unstable stratification resulting from low-level convergence and high-level divergence in the afternoon is also established 2 hours before the heavy precipitation, and the maximum divergence corresponds well to the heavy precipitation.Radar observations indicate that the precipitation is dominated by low-centroid warm clouds with high precipitation efficiency.The surface convergence line triggers convection, which gradually develops into a belt-shaped convective system.Judging from the results of the numerical forecast, the model failed to report the impact of the city's underlying surface on meteorological elements, and the forecasting surface convergence line was lagging and weak, leading to the forecasting difficulties of heavy precipitation.