An extreme flash rain event that occurred in Xiamen under the background of subtropical high on 11 August 2021 is analyzed based on X-band dual-polarization phased array radar observations. Dynamic and microphysical characteristics of the precipitation system are analyzed using the Doppler radar wind field retrieval technique combined with high-precision topographic data. The study yields the following results. (1) The event took place under the control of the subtropical high with the characteristics of weak synoptic-scale forcing. The surface wind convergence line promoted the formation of a quasi-linear convective system (QLCS), and the back-building process of the QLCS led to local extreme precipitation event. (2) The updraft lifted the raindrops to the mid-level, forming a large particle accumulation layer. When it descended, the rain intensified. The configuration of inclined updraft and downdraft ensured that the falling of large particles would not suppress updraft, which is favorable for the development and maintenance of convective system. The downdraft triggered the development of the upstream convective system, forming a back-building process. (3) The impact of local terrain on the precipitation system was highlighted under the weak synoptic scalebackground. The low-level convergence induced by local terrain caused the polarization parameters such as differential reflectivity (ZDR) and specific differential phase (KDP) to increase significantly on the windward slope, and the large value area was maintained there. The larger denser precipitation particles produced extremely high precipitation efficiency. (4) The warm rain process and the ice phase process coexisted in this extreme precipitation event. The warm rain process played a major role in the formation of rain, and the melting of ice particles accelerated this process. (5) At high rain rate, the breakage and collision of raindrops tend to balance, and the increase of rain rate depends on the increase of raindrop concentration. Therefore, ZDR can be used to determine whether the rain rate is increasing. (6) The evolution of the ZDR and KDP column is an appropriate index that can reflect the development of the surface rain rate. During a continuous precipitation process, the re-development of the ZDR (KDP) column height occurs earlier than that of the precipitation system.

为分析强降水超级单体风暴的偏振特征及其动力和云物理结构,利用厦门海沧双偏振雷达数据及常规观测资料,采用多普勒雷达风场反演和粒子相态识别等技术,对2018年5月7日发生在闽南地区的一次导致特大暴雨的强降水超级单体风暴进行了分析,研究表明:(1)相关系数小值区出现在有界弱回波区和钩状回波之前,可指示低层上升气流的位置.(2)在前侧下沉气流南侧的反射率因子梯度大值区附近,存在一个浅薄的差分反射率因子大值区(差分反射率因子弧),其形态与超级单体的发展程度有关.在本次过程中差分反射率因子弧先于钩状回波和中气旋出现,对超级单体的发展具有较好的指示性.(3)在中层的融化层上,差分反射率因子大值区和相关系数小值区呈环形围绕在上升气流周围.差分反射率因子环和相关系数环对确定中层上升气流的位置具有指示意义.(4)差分反射率因子柱位于有界弱回波区的上方,并位于主上升气流附近,在仅有单部雷达进行观测时,差分反射率因子柱可用于识别主上升气流的位置.(5)差分相位常数柱主要由大量混合相态水凝物造成,其位置与地面雨强中心存在较好的对应关系.

利用1980～2017年厦门逐小时降水资料和NCEP再分析资料,分析厦门地区极端降水事件的气候特征,并初步讨论其成因。研究结果表明:1)极端降水事件的年发生频率呈现减少的趋势,厦门岛的减少趋势要比内陆更为显著。2)小时尺度的极端降水事件在较小尺度空间内无论是发生频率还是强度都存在明显的区域性差异,内陆地区在发生频率和强度上均高于厦门岛,但强度的平均值一致。3)造成极端降水事件的天气系统有4类,分别是热带气旋型、冷式切变型、西南风气流型和低槽冷锋型。随着城市抗灾能力的提升,对极端降水预报的要求也不断提高,基于小时值的结论可以为未来厦门地区极端降水事件的预报提供参考基础,进而提升预报的有效性和针对性。

受2015年第13号台风“苏迪罗”影响,福州出现特大暴雨.为研究台风登陆前局地强降水与地形的关系,针对福建长乐雷达的0 °仰角数据进行了风场反演,得到福州低空风场在强降雨发生时的结构及演变特征,综合利用NCEP 1 °×1 °再分析资料及福州三维地形数据,探索了福州地区持续性短时强降水的发生原因.结果表明:(1)“苏迪罗”影响期间正值南海季风爆发期,为台风提供了充沛的水汽;(2)强降雨发生时,福州地区存在正涡柱,配合强烈上升运动,为短时强降水的发生提供良好的动力条件;(3)雷达风场反演显示:当福州环境风场为东北气流,有一持久、稳定的分流区出现在福清北部,随着台风靠近,环境风逐渐由东北转为偏东风,分流区的位置也一直向内陆延伸,分流气流与台风环境气流形成了明显的辐合带,激发了螺旋雨带内中尺度对流云团的发生发展,造成短时强降水;(4)台风环境气流进入福州后出现的分流现象与福州的盆地地形有关.

对2000年以来5个在粤东登陆的、对厦门有较大影响以上的台风,并按类型、路径、生成区域、影响程度等进行分析,找出了冷空气及西南季风对影响厦门的台风所带来的风雨影响特征,以期对台风业务预报有所帮助.

Numerical simulation is made on the heavy rainfall over the Huaihe valley on 3 to 4 July 2003 using the PSU/NCAR MM5 model.It is revealed that the MM5 model performed quite well in simulating and can provide high-resolution data for diagnosis.The meso-α-scale and meso-β-scale convective systems of about 100 km can be simulated out by the MM5 model,but the model has a limited capability in simulating the meso-β(γ)-scale systems of smaller scales or more strongly developed systems.The direct reason of the heavy rainfall event is the rapid development of the about 100 km long meso-β-scale convergence zone at the lower levels,which is validated by the high-resolution data provided by the MM5 model.The mechanisms and the 3D structure of the mesoscale convergence zone are obtained by the diagnostic analysis of the physical quantity field characteristics.