平流层/对流层相互侵入背景下梅雨锋暴雨的中尺度双雨带结构的形成和维持机制研究

Stratospheric-tropospheric bi-directional intrusion could cause varied types of tropopause folding or breaking, which is an outstanding atmospheric disturbance phenomenon at middle level of atmosphere. It is well known that these disturbances have closed relationship with the occurrence and evolution of the mesoscale convective systems and may be used as an important criterion for severe weather forecasting.This project is designed to study troposphere-stratosphere bi-directional intrusions and their relationship with the rainstorm occurred over Yangtze river areas during Meiyu season on the basis of satellite data, numerical modeling, trajectory analysis and some other diagnostic analysis tools. Specifically, the study will try to answer thee key questions which as follows are: 1)characteristics of intensity and spatial distribution of the stratospheric-tropospheric bi-directional intrusions which related to the meso-scale double rainbands structure; 2)the effects of convetive intrusions in the form and maintanance of the double rainbands; 3) relationship between stratospheric-tropospheric bi-directional intrusions and the strength alternation within two rainbands. To some extent, introducing the new conception of the stratospheric-tropospheric bi-directional intrusion into the study of mechanism of Meiyu front rainstorm, estimating the strength of the stratospheric-tropospheric bi-directional intrusion related to rainstorm based on satellite and numerical modelling,as well as some new physics parameters under moist circurmstance for stratospheric intrusion strength estimation are creative trials. Through this study, it is expected to deepen understandings of the relationship between the turbulence at middle level of atmosphere and rainstorm, as well as to enhance our ability of the satellite data application in objective detection and analysis of the middle-level atmosphere disturbances, by which to improve monitoring and warning capabilities of the severe disasters.

平流层与对流层空气相互侵入可以形成多种形态的对流层顶折叠或断裂。这是一种突出的中层大气扰动现象。它与中尺度对流系统发生发展具有密切关系，可用作强天气预报的重要判据。本项目拟综合应用卫星观测、数值模拟及气流轨迹分析等资料和方法，以梅雨锋中尺度双雨带为对象，重点研究三个关键问题：1）引起中尺度双雨带结构的平流层/对流层相互侵入强度和范围特征；2）对流层向平流层侵入在中尺度双雨带的产生和维持中的作用；3）平流层/对流层相互侵入与梅雨锋中尺度双雨带强弱交替变化特征的关系。本项目在江淮梅雨锋暴雨的机理研究中引入了平流层与对流层空气相互侵入的新观点，基于卫星观测和数值预报资料估算平流层/对流层相互侵入强度，并在与暴雨有关的平流层侵入强度估算中引入湿大气条件下的物理参数等均为创新性尝试。研究有助于深化对中层大气扰动的形态、机理及其与灾害性天气关系的认识，为业务预报提供科学依据和线索。

项目实施4年期间，按照项目计划，围绕项目原定的2项主要研究内容，采用观测资料和数值模式相结合的手段，先后使用了FY、TRMM、MODIS、CALIPSO、OMI等卫星资料、NCEP、ECMWF和GEOS-5/MERRA-2再分析资料、常规资料、飞机AMDAR资料以及数值模拟结果。从定量反演方法、天气气候特征以及形成机理等方面展开。通过研究具体取得的成果，包括：1）创新地基于风云气象卫星成像仪多通道成像特点，结合数值预报资料，利用机器学习的随机森林法，建立了实时估算对流层顶气压、高度以及温度、风场的方法；2）基于卫星反演的动力对流层顶气压，使用气压梯度与对流层顶折叠强度的关系，建立了对流层顶深度以及穿透性对流深度估算模型；3）从统计分析结果看，6-7月我国中纬度地区双雨带结构的暴雨日数占总暴雨日数的56%，发生频次较多，长江中下游地区梅雨锋暴雨期间多出现南北两条双雨带平行分布的现象；4）双雨带北侧雨带相比南侧雨带更强可能与北侧附近的对流层顶折叠强度较强有关。5）通过数值试验初步分析表明对流层顶高度降低以及高层风垂直切变的增加可能是导致双雨带产生的重要的高层动力条件；6）穿透性对流对双雨带结构的产生并没有直接影响，但是穿透性对流产生对所在的雨带的强度增强具有指示意义。7）当发生穿透性对流时，增强的红外云图上常常会出现的一种冷圆环（cold ring）或U/V字形（cold U/V）结构。8）高空急流激发的重力波，在发展过程中破裂可能是导致在对流层顶折叠附近的强对流云团对流加强。在上述研究基础上，项目共发表专著1部，相关论文7篇，其中4篇SCI，1篇核心期刊论文，2篇会议论文，申请2项国家发明专利，建立了一套软件系统。.通过本项目研究，一方面，补充并完善了对我国长江流域夏季梅雨锋暴雨的天气气候特征的认识，从高层大气的影响角度深化了对这类暴雨出现分裂雨带特征的理解，另一方面，项目研究过程中发现的与灾害性天气强度变化有关的大气高层变化特征，特别是在卫星观测资料上的表现，为业务预报提供科学依据和线索。