致灾下击暴流雷达特征结构及成因研究

Downburst was discovered by Fujita for it caused lots of aircraft accidents. Downburst is defined as an outburst of damaging winds on or near the ground which induced by a strong downdraft. The horizontal dimensions of divergence wind are less than 10km and damage wind can reach F3. China experienced a lot of microburst-related damage wind accidents these years. This project will focus on damage downburst, including isolated storm downburst and embedded downbursts, the latter is downburst embedded within the mesoscale convective systems. This study will cover the following topics, the radar signatures of downburst storm investigated by Doppler weather data, the physical process of downburst formation, and the Effects of the low level vertical wind shear, PBL convergence line and the outflow boundary on the storm structure and Intensity of downburst, the mechanism of embedded downburst, the organization structure of different scale downdraft and the dominant factors that affect the evolution of downburst, the different contributions of mesoscale and convective-scale downdrafts to damaging downburst. The research is based on observational study of real cases mainly through radar data, and then studied by the Variational Doppler Radar Analysis System (VDRAS) which assimilated Doppler weather radar data and conventional observation data to WRF model. Cloud model will be used to perform sensitive examination. In order to provide a theoretical basis for the downburst nowcasting, this study try to perform a systematic research on downburst in China.

下击暴流（downburst）因造成飞行事故而被Fujita发现，气象上定义为强下沉气流引起的地面及近地面水平尺度小于10km的灾害性辐散风，其破坏力可达F3级。近年来我国多次因下击暴流造成重大人员伤亡。本项目研究对象为致灾下击暴流（25m/s以上），包括孤立风暴造成的致灾下击暴流和中尺度对流系统内嵌的致灾下击暴流。研究内容包括：基于多普勒天气雷达观测资料研究下击暴流风暴的特征结构及下击暴流形成的物理图像；低层风垂直切变、边界层辐合线、出流边界等对风暴结构和下击暴流出流强度的影响；中尺度对流系统内嵌的致灾下击暴流形成机理分析、不同尺度下沉气流的组织结构及支配其演变的热动力因子研究、不同尺度下沉气流及冷池等对致灾下击暴流的贡献。本项目以雷达观测分析为主，辅以融合多源观测和数值模拟数据的分析系统和云模式敏感性试验，尝试对中国致灾下击暴流进行相对系统的研究，以期为下击暴流临近预报提供理论依据。

下击暴流指对流单体强下沉气流引发的地面或地面附近的爆发性辐散出流（Outburst），单个下击暴流会导致公里（km）尺度的小范围地面强阵风，而下击暴流簇可导致较大范围间断性地面灾害性强阵风，其形成机制亦不限于强下沉气流辐散。近年来我国多次因下击暴流造成重大人员伤亡和财产损失。本项目主要基于多普勒天气雷达资料和探空资料对于产生下击暴流的风暴结构特征、环境条件和强风形成物理机制等进行研究，内容及相关成果包括：1）基于56例超级单体灾害性大风个例的多普勒天气雷达资料总结出了有利于产生致灾下击暴流的超级单体关键雷达回波特征的量化结果，给出了产生致灾下击暴流的超级单体与非致灾超级单体风暴结构的差异；2）研究给出了中国大范围雷暴大风事件（即Derecho事件）的环流型、环境要素和风暴结构特征，基于典型个例对中尺度对流系统内嵌的极端强风事件形成物理过程进行了分析；3）基于探空资料对比95例极端强风事件和95例普通雷暴天气的环境差异，在此基础上提炼出了30m/s以上极端强风的环境要素特征；4）分析了边界层中尺度系统和风暴活动产生的阵风锋对强风事件的影响，研究了无明显大尺度系统强迫的致灾强风风暴结构特征、发展维持机制和物理过程。本项目对中国致灾下击暴流进行了相对系统的研究，研究成果为下击暴流临近预报预警提供了研究支撑，部分成果通过培训在全国范围内推广应用。