青海东部两次大暴雨过程雷达产品特征对比分析

Comparative Analysis of Radar Product Characteristics During Two Heavy Rainstorms in Eastern Qinghai

利用西宁多普勒雷达探测资料对2013年8月21-22日西宁大通桥头和2018年8月2-3日、3-4日海东乐都中坝乡的两次大暴雨降水过程雷达产品(强度、速度、累计降水估计产品)特征进行对比分析并初步获得强降水的临近预警指标,结果表明:(1)前者过程降水对流性强,回波强度大,60 dBZ以上回波在大暴雨区维持时间近3小时,短时降水强度大;后者雷达回波强度相对偏弱为20 dBZ,稳定性降水回波影响时间长,回波移动性大,雨强均匀,形成列车效应。(2)两个过程径向速度场上均出现逆风区或辐合区,对强降水的开始有指示意义,与降水中心相对应,前者风场辐合区特征强于后者,对应小时雨强大,逆风区维持时间反映出降水集中时段;后者强降水区高低层冷暖平流分布明显,反映出环境场的不稳定特征。雷达风廓线产品对强降水发生、发展、结束具有较好的指示意义,前者由于降水强度大,风场伸展高度更高,前者强降水发生前一小时整层风向标消失转为“ND”区控制,后者风场上持续出现的低层风切变对降水的维持起到很大作用;降水趋于结束时,风场均表现为无序或乱序。(3)雷达1 h(OHP)和3 h(THP)降水估测产品对两个过程中的降水落区及范围估测均具有一定参考性,但1 h和3 h雨强分别超过20 mm/h、50 mm/h时,降水估测值才会更接近实况降水量,故产品对大通桥头过程的降水量估测更具有可预报性。研究结果可为以后此类极端性降水天气的发生时间和降水强度的短临预报提供参考依据。

Using the detection data of Doppler radar in Xining,this paper compares and analyzes the characteristics of radar products(intensity,velocity,cumulative precipitation estimation products)of two heavy rainstorms in Datong Bridgehead in Xining on August 21-22,2013 and Zhongba Township,Ledu,Haidong on August 2-3 and 3-4,2018,and preliminarily obtains the near warning indicators of heavy precipitation.The results show that:(1)The former process has strong convection and large echo intensity,and the echo above 60 dBZ lasts for nearly 3 hours in the heavy rainstorm area.The short-term precipitation intensity is large,the radar echo intensity of the latter is relatively weak by 20 dBZ,the stable precipitation echo has a long influence time,the echo mobility is large,and the rain intensity is uniform,forming a train effect.(2)The headwind zone or convergence zone in the radial velocity field of the two processes has indicative significance for the beginning of heavy precipitation,corresponding to the precipitation center.The former wind field convergence zone characteristics are stronger than the latter,corresponding to strong hourly rain,the maintenance time of the headwind zone reflects the precipitation concentration period.In the latter heavy precipitation area high and low cold and warm advection distribution is obvious,reflecting the unstable characteristics of the environmental field.Radar wind profile products have good indication significance for the occurrence,development and end of heavy precipitation.Due to the high precipitation intensity,the wind field extension height of the former is higher,and one hour before the occurrence of heavy precipitation,its whole layer of wind vane disappears into“ND”area control.The wind field of the latter continues to appear low-level wind shear,which plays a great role in the maintenance of precipitation.When the precipitation tends to end,the wind field is disorderly or out of order.(3)Radar 1h(OHP)and 3h(THP)precipitation estimation products have certain reference for the estimation of precipitation falling area and range in the two processes,but when the rain intensity exceeds 20mm/h and 50mm/h in 1h and 3h respectively,the precipitation estimation value will be closer to the actual precipitation,so the product has more predictability for the precipitation estimation of the Datong Bridgehead process.