台风“利奇马”北上锋生导致山东省创纪录暴雨天气学成因分析

SYNOPTIC ANALYSIS OF THE EXTREME RAINFALL IN SHANDONG PROVINCE CAUSED BY THE FRONTOGENESIS OF TYPHOON LEKIMA DURING ITS NORTHWA RD MOVEMENT

利用常规气象观测、NCEP/NCAR再分析、风廓线雷达及逐时自动气象站降雨量等资料,对2019年8月10—13日台风“利奇马”造成山东省有气象记录以来最大一次特大暴雨进行了成因分析。结果表明:(1)此次台风特大暴雨主要为中低纬系统相互作用及台风倒槽直接影响产生,其与冷空气密切相关,冷暖空气交汇的位置正对应强降水落区;(2)特大暴雨发生在θse密集带上冷暖空气交汇的对流不稳定强烈发展的锋生区域。锋生大值中心与特大暴雨中心对应较好,锋生强度对未来6小时降雨预报有指示作用;(3)切变变形锋生为总锋生的主要正贡献,强降水区位于θse密集带上风向曲率最大的地方,在台风预报业务中要注意等θse线密集带上是否出现“对头风”的明显风向切变;(4)强锋生次级环流与台风倒槽辐合及冷暖空气交汇等共同作用导致动力抬升快速增强,促使对流不稳定能量大量释放形成强降水。锋生次级环流上升支最强的区域,正对应降水最强的区域,也是冷暖空气交汇区域;(5)风廓线雷达超低空风场的变化对小时雨强大小有明显的指示意义。近地面层风向发生突变,由东南风转北风的时段与潍坊出现山东全省最大小时雨强的时段一致。低空急流向低空的快速扩展对应着短时强降水的开始。近地面层暖平流的强弱变化影响着此次强降雨的雨强大小。

Based on the conventional meteorological observation data,the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR),the wind profile radar data,and the hourly precipitation data from automatic weather stations,synoptic analysis of the severest extraordinary heavy rain ever recorded in Shandong Province caused by Typhoon Lekima from August 10 to 13,2019 are studied in this paper.The results show that this typhoon heavy rainfall episode is mainly caused by the interaction of the middle and low latitude weather systems,as well as the typhoon inverted trough.Moreover,it is closely related to cold air.The place where the cold and warm air intersects is the area where heavy rainfall occurs.This extraordinary heavy rain episode occurs in the frontogenetical area in the dense area of iso-θse(potential pseudo-equivalent temperature)lines,where the convergence of cold and warm air leads to the strong development of convective instability.The large-value center of frontogenesis has good correspondence with the center of the extraordinarily heavy rain,and the intensity of frontogenesis can well indicate the rainfall intensity in the next 6 hours.The positive contribution of the total frontogenesis mainly comes from the shear deformation.The area with heavy precipitation is located in the place with the largest curvature of wind direction in the dense area of iso-θse lines.Thus,in the typhoon forecast operation,whether there is an obvious wind direction shear of"opposite wind"in the dense area of iso-θse lines should be noted.With strong water vapor transport and strong convective instability formed by the low-level jet,the combined effects of the convergence in the typhoon inverted trough,cold-warm air convergence and strong frontal secondary circulation lead to a rapid intensification of the dynamic lifting.Therefore,with the release of convective instability energy,heavy rainfall occurs.The area with the strongest ascending motion of the frontal secondary circulation corresponds to the area with the strongest rainfall,which is also the area where the cold and warm air intersects.The variation of the wind field in ultra-low levels from the wind profile radar has important indicative significance for the rainfall intensity.