夏季青藏高原东移云团引发长江流域暴雨的研究

The heavy rainstorms over the Yangtze River Basin (YRB) frequently associated with the eastward-moving cloud clusters from the Tibetan Plateau (TP) is one of the difficult points in operational weather forecast. It may be the direct reasons that the environmental parameters and thermodynamic mechanism for the mesoscale systems of the YRB heavy rainstorms induced by these cloud clusters are not clearly understood. In this proposal, the data sets issued by observational network and being obtained by the planning stations in the path of these cloud clusters will be used to analyze the macro and micro parameters’ characteristics of the eastward-moving cloud clusters. Using the methods of numerical simulation, thermodynamic diagnoses, and the high-resolution of reanalysis data, the changes of atmospheric environment induced by the eastward-moving cloud clusters will be analyzed. Both typical cases and large-sample statistical results will be used in diagnosing the key thermodynamic factors of the rainstorms triggered by the eastward-moving cloud clusters over the TP. Based on the observation and analyses shown above, a conceptual model containing the thermodynamic key features of the rainstorms triggered by the eastward-moving cloud clusters will be established. Furthermore, the cloud and atmospheric environmental parameters derived from the observation, the diagnostic results, and the mesoscale model parameterization schemes will be investigated thoroughly, so as to determine the best parameterization scheme for the rainstorms triggered by the eastward-moving cloud clusters. A large number of simulations on the historical rainfall cases will be conducted to evaluate the determined parameterization scheme. Finally, the applicability of the rainstorm conceptual model, and the key thermodynamic factors of the heavy rainfall events induced by the eastward-moving cloud clusters over the TP will also be evaluated in detail.

夏季青藏高原云团东移常常引发长江流域强暴雨，这类暴雨的预报是业务难点之一，其直接原因是我们还不清楚高原云团东移引发长江流域暴雨的大气中尺度系统的环境参数和热动力机制。基于此，本项目拟利用高原现有观测网和项目计划增加的云同东移路径上关键点的观测，来分析青藏高原东移云团的宏观和微观云参数特征；结合再分析资料，采用模拟、热动力诊断相结合的方法，分析高原东移云团引发长江流域暴雨的大气环境场特征。在此基础上，个例与统计相结合，诊断高原东移云团引发长江流域暴雨的关键热动力因子，从而建立高原东移云团引发长江流域暴雨的概念模型。并将观测和诊断得到的云团参数及大气环境参数与中尺度模式不同参数化方案给出的结果进行对比，获得云团东移影响长江流域暴雨过程的最佳参数化方案，然后通过数值试验，检验青藏高原东移云团引发长江流域暴雨过程的天气学模型及关键动力热力因子的适用性。

由于夏季青藏高原云团东移常常引发长江流域强暴雨，本项目针对此类暴雨形成机理开展了高原观测试验、云团东移特征、高原山谷风环流、环境条件、云团与高原涡和西南涡相互作用机理、云微物理参数化方案评估和敏感性试验等工作。主要结果如下：1.建立了高原东侧和长江中游2017-2020年科学试验的综合观测数据集，揭示了高原东侧大气层结日变化特征，云垂直分布特征，层云中冻结层和融化带的冰相粒子特征，对比分析了高原与长江中游云宏微观特征的差异。2.揭示了高原东移云团的宏微观属性：云团东移多层云增多，对流云增加，层云下降；统计得到影响长江流域暴雨的高原云团移动路径有三条：东移(41%)、先东南移后折向东北(40%)、先向北后东南移动(39%)。3.合成了高原东移云团影响长江流域暴雨的环境条件，其中在3Km高度存在一支由高原上向东输送到达长江流域的水汽通道(17%)。4.诊断了高原云团东移过程能量转换机制，能量自西向东传播，存在明显的各分项能量向扰动动能转换和波流相互作用。5.建立了山谷风环流模型及其与西南涡(九龙涡)的可能联系，高原东侧存在显著的定常山谷风环流。6.发现了两类高原涡和高原MCS相互作用的高频事件：高原MCS触发新生的高原涡、高原涡与高原MCS的相互作用；诊断了两类事件的动力和热力因子，并凝练了物理概念模型。7.揭示了高原MCS对下游降水及西南低涡影响的机理。8.开展了云微物理参数化方案的评估、敏感性试验及改进和分析工作。重新拟合了雨滴下落末速度和雨滴谱的二项式关系，改进了模式降水预报。9.开展了高原云团东移引发暴雨的云微物理过程研究。比较了移出和未移出四川盆地暴雨的云微物理特征，检验了冰相粒子对该类降水的重要性和过冷水分布的观测特征。10.检验了青藏高原东移云团引发长江流域暴雨的热、动力特征。11.发表相关文章56篇，其中SCI 25篇。项目培养了3名博士，10名人员晋升了职称。