青藏高原大气绕流和爬流三维结构异常变化对下游地区暴雨天气的影响研究

The Tibetan Plateau(TP) is the upstream strong signal area for severe weather in China. The changes of its dynamic structure have important impact on precipitation over its downstream areas. Due to the limitation of observing conditions in the past, the spatial and temporal resolution of sounding and surface observations in TP area is very low. The reliability of foreign reanalysis data in TP area is also not very well due to the complicated terrain effect of TP. These factors directly affected the accuracy of former analyses on the 3D structure features of the flow around and flow over Tibetan Plateau (FFTP) and weather forecast of its effects on rainstorms over its downstream areas as well as on the numerical model simulation and prediction abilities on it. Previous researches on FFTP were mainly based on the climatological analyses and on the effect of its strength change on seasonal precipitation over its downstream areas. Few studies were focused on the effects of the FFTP abnormal structures on rainstorms over its downstream areas. With the development of AWS, GPS and new operational L-band radiosonde observation systems in TP and its surrounding areas, the observational ability over TP was improved remarkably, which can provide more observations with high resolution. Furthermore, the satellite remote sensing data can be variationally corrected by radiosonde data which can provide 3D high resolution observations. The combining of above observational data makes it possible to investigate the detailed 3D structure of FFTP. So by utilizing the above multi-source observations, this project plans to investigate the abnormal spatial-temporal variation of FFTP 3D structures during the process of rainstorms over TP downstream areas, its interaction with thermal forcing of TP as well as the possible impacts of its abnormal changes on rainstorms. Numerical assimilation experiments will further be carried out to investigate the physical mechanism of above phenomena. The aim of this study is to enhance our understanding of the impacts of dynamical and thermal forcing of TP and provide new scientific basis for improving the weather forecast to rainstorm.

青藏高原是中国区域灾害性天气的上游强信号区，其大气动力结构的异常变化对下游降水具有重要的影响。受资料条件限制，以往高原绕流和爬流的研究大多是在气候时间尺度上分析其强度变化对下游季节性降水的影响，针对其异常三维结构对下游灾害性暴雨天气影响方面的研究很少。近年来随着高原自动气象站、周边GPS观测网及新型业务探空站的建成，观测基础得到了极大改善，卫星遥感资料经变分订正再分析可得到三维高分辨率观测数据，以上多源观测资料的综合应用使得高原绕流和爬流三维结构的细致分析成为可能。本项目拟利用青藏高原大量的新观测资料结合卫星遥感再分析数据，针对下游灾害性暴雨天气过程，研究青藏高原大气绕流和爬流三维结构异常变化特征及其与高原热力过程的相互作用，研究其对下游暴雨的影响，并通过数值同化试验探讨这种影响的物理机制。通过上述研究以深化对高原动力、热力作用的认识，并为提高高原下游区域暴雨预报准确率提供新的科学依据。

青藏高原是中国区域灾害性天气的上游强信号区，其大气动力结构的异常变化对下游降水具有重要的影响。受资料条件限制，以往高原绕流和爬流的研究大多是在气候时间尺度上分析其强度变化对下游季节性降水的影响，针对其异常三维结构对下游灾害性暴雨天气影响方面的研究很少。. 针对此问题，项目首先围绕青藏高原地区大气绕流、爬流异常结构特征，对中国东部地区区域持续性暴雨过程进行了统计研究，注意东部地区存在三个典型的区域持续性强降水类型：华南型、江南型和江淮型，且这三种类型区域持续性暴雨过程中，高原及周边地区近地层及中高层大动力及热力结构存在显著的差异。不同的降水类型，高原周边及其主体地区近地层风场的分布特征有所不同，不但风场的强度和位置有所差异，而且在高原主体上空风场辐合上升运动的区域也不尽相同；同时，青藏高原区域的热力状况也有所差异。上述诊断分析结果进一步提高了高原地区绕流、爬流环流结构变化对长江中下游地区的强降水变化影响的认识。. 进一步采用高原及周边地区日益增多的多源观测资料，开展了多源观测资料在数值中的变分同化应用研究。研究注意到，变分订正后的卫星遥感资料比常规再分析资料在高原地区更能真实的反映高原大气实际的层结状况，尤其对湿度场的改进较为明显，为模式提供了与实况更为一致的物理量，可以明显地改进数值模式对高原下游地区暴雨的模拟水平。雷达反射率资料可为模式提供更优初值，不但为初值场中增加逐时降水信息，提高了模式预报效果，且对中小尺度系统演变刻画得更加清晰。L波段高空气象探测数据可以反映更多的大气垂直结构信息，且模拟结果中垂直结构信息能够更有效地改进水汽的输送过程以及强水汽的输送位置的描述。上述研究不但为多源观测资料在数值模式中同化应用开拓了思路，也将通过高分辨率数值模式结果，进一步分析和探讨青藏高原大气绕流和爬流三维结构异常变化特征对其下游地区暴雨影响的物理机制。

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