基于最优化理论的双偏振雷达台风降雨反演技术研究

China is frequently influenced by typhoons. To improve the capability of quantitative monitoring of typhoon precipitation is of great significance for meteorological disaster prevention and mitigation. Compared to the conventional weather radar, polarimetric radar can obtain more physical information of rain, which helps to retrieve raindrop size distribution (DSD) and improve quantitative precipitation estimation (QPE). Thus, polarimetric radar is an important approach for typhoon precipitation surveillance. The model error and measurement error are two major factors which affect the accuracy of typhoon rainfall estimation using polarimetric radar data. The objective of this proposal is to establish the statistical shape(μ)-slope(Λ) relationship of gamma distribution for different typhoon regions (inner and outer rainbands), using typhoon observations from the 2D-video disdrometers deployed in east and south China. It will improve the model accuracy of typhoon DSD retrieval and QPE. On this basis, a variational algorithm will be developed for optimized typhoon DSD retrieval and QPE from polarimetric radar measurements. The impact of measurement error will be mitigated in this algorithm. The accuracy of QPE in different regions of landing typhoon (inner and outer rainbands) will be validated against the gauge measurements in specific typhoon cases at last. This study will help to improve the capability of quantitative monitoring of typhoon precipitation, which would lay the foundation for the polarimetry-upgrade of operational weather radar network.

我国受台风影响频繁，提高对登陆台风降水的定量监测能力，对于气象防灾减灾具有重要的意义。双偏振雷达相比于常规雷达可以观测降雨的更多物理信息，可用于反演雨滴谱并获取更准确的降雨估测，是监测台风降水的重要手段。模型误差和观测误差是影响双偏振雷达定量降雨估测精度的两种主要因素。本项目拟基于华东和华南地区的二维视频滴谱仪观测，建立适用于台风不同区域（内、外雨带）的Gamma分布形状参数μ和斜率参数Λ之间的统计关系，优化台风雨滴谱反演和降雨估测模型；并在此基础上，建立基于变分的双偏振台风雨滴谱最优反演方法，以降低观测误差对降雨反演的影响；最后，选择典型登陆台风分析其不同区域（内、外雨带）的降雨估测精度。本项目有利于提高台风降水定量监测能力，为业务天气雷达网的双偏振升级提供技术支撑。

我国受台风影响频繁，提高对登陆台风降水的定量监测能力，对于气象防灾减灾具有重要的意义。双偏振雷达相比于常规雷达可以观测降雨的更多物理信息，可用于反演雨滴谱并获取更准确的降雨估测，是监测台风降水的重要手段。经过三年的研究，建立了基于变分的双偏振雷达雨滴谱反演、降雨估计、比差分相位计算和衰减订正一体化最优模型，并实现了台风雨滴形状特征在降水估计中的实时最优估计，优化台风降雨和微物理特征反演。雷达估测的台风小时降雨量与雨量站观测相关系数超过0.9，均方根误差为2.42 mm。同时，利用沿海双偏振雷达观测，结合 Himawari-8卫星等手段，从统计和个例的角度分别研究了台风的暖雨和冰相微物理过程对降水的作用。统计研究发现，台风内核、内雨带和外雨带中自转化和碰并等暖雨过程是主导的微物理过程，外雨带中凇附等冰相过程对降水量和粒子的增长具有重要作用。针对超强利奇马（2019）降水微物理的非对称结构个例研究发现，在登陆过程中利奇马（2019）台风上风切强降水区域是自转化等暖雨过程主导。由于涡旋罗斯贝波锁相作用在上风切左右两侧作用的差异，上风切右侧相比于左侧上升气流更强，凇附等冰相过程作用显著，与低层暖雨过程一起造成低层强降水。上述研究，一方面改善了双偏振雷达的台风降水定量估测精度，另一方面深化了对台风微物理结构过程及其对降水作用的认识。