低频夏季风环流背景下热带西北太平洋天气尺度波列发展的机理研究

A close association between synoptic-scale wave trains (SWTs) and low-frequency summer monsoon circulations over the tropical western North Pacific has been widely documented. In spite of some existing studies in this field, it remains largely unknown regarding key processes responsible for the development of SWT activity under the background of the low-frequency summer monsoon circulations, which leaves us disadvantaged in conducting weather/extended-range forecast..This proposed research is aimed at improved understanding of key physics in regulating SWT by the low-frequency summer monsoonal circulations based on the observations and new modelling database including 27 climate simulations from the MJOTF/GASS (MJO Task Force (MJOTF), under the auspices of the “Year of Tropical Convection” (YOTC) and the Global Energy and Water Cycle Experiment (GEWEX) Atmospheric System Study (GASS)) model evaluation project. Four main objectives of this proposal are: (1) to investigate evolution features of SWT activity on the intra-seasonal time scale, including its propagation, vertical/horizontal structures, and accompanying energy exchange and transport. The relationship between summer monsoon circulations and SWTs on the intra-seasonal time scale will be deeply explored; (2) to assess the capability of 27 climate simulations provided by the MJOTF/GASS project in simulating the SWT activity under the background of low-frequency summer monsoonal circulations. The relative importance of environment factors associated with low-frequency monsoon circulations in affecting the simulations of SWT activity will be characterized; (3) to explore the key dynamical and thermo-dynamical processes closely associated with the low-frequency summer monsoon circulations as well as the SWT activity based upon the theory of tropical dynamics and the diagnosis of energetics evolution; (4) to conduct a series of numerical experiments with ideal cases, sensitive cases and specifically selected observed cases to further reveal the associated mechanisms on the multi-scale interactions between low-frequency summer monsoon circulations and SWT activity..Results of this proposal will greatly improve our understanding of the essential physical processes in modulating SWTs under the background of low-frequency summer monsoon circulations, which provide scientific foundations for the predictability of weather events on intra-seasonal time scales. This study will thus benefit weather/extended-range forecast over the tropical western North Pacific.

项目将基于MJOTF/GASS模式评估项目提供的最新一代27个全球大气环流模式资料集研究低频夏季风环流背景下热带西北太平洋天气尺度波列发展机理。为此，将(1)利用观测资料系统分析低频夏季风环流背景下天气尺度波列的空间结构、传播特征和能量演变过程，揭示夏季风环流和天气尺度波列的季内演变规律及其关联；(2)评估多模式资料对低频夏季风环流背景下天气尺度波列的模拟性能，寻求影响其模拟性能的重要因子和物理过程；(3)结合(1)与(2)的研究结果，应用动力学理论分析和能量诊断方法探讨与季风环流型式有关的物理过程在天气尺度波列季内变化中的作用，揭示影响天气尺度波列季内变化的关键物理过程，并给出物理概念模型；(4)设计一系列数值试验，揭示相关的物理机制。预期项目完成将不仅深化认识热带西北太平洋地区低频夏季风环流背景下天气尺度波列发展的物理本质，同时有助于提高热带西北太平洋地区的天气/延伸期预报水平。

本项目属于台风气候动力学领域，在该国家自然科学面上基金的资助下2017-2020年期间，项目申请人和项目组成员围绕项目研究目标，紧扣研究任务展开研究，取得了一批具有影响力的研究成果，在国际主流SCI期刊Journal of Climate, Climate Dynamics已发表学术论文32篇（SCI论文28篇），其中以项目主持人为第1作者/通讯作者身份发表SCI论文共17篇，相关研究成果被美国科学院院士Emanuel教授、中国科学院院士陈大可教授、中国科学院院士丁一汇研究员等一批国际知名专家及其合作者正面引用。独立指导硕士13名和协助培养博士3名。.项目的研究结果归纳如下：①系统地评估了全球最新27个高时间分辨率的气候模式对天气尺度波列的模拟性能；②揭示了低层季风环流及其正压能量聚集是天气尺度波列发展的关键物理过程。③揭示了多类季内热带波动对天气尺度波列和台风生成的调制作用，指出了低层相对涡度和中层水汽为影响台风生成季节内变化的两个重要因子；④从热带波动大尺度调制作用的角度出发，提出了评估不同热带波动与台风生成关联性的新方法，证实了低频波动本身也可提供台风生成必需的初始扰动；⑤揭示了ENSO不同状态背景下季内振荡对台风生成的调制作用的显著差异，提出了年际尺度边界水汽异常分布对此调制作用的关键作用。⑥揭示了影响台风生成的重要因子和热带洋区海温分布调制台风生成的重要作用，提出了大尺度大气-海洋强迫驱动台风生成和快速加强的可能物理机制。⑦揭示了台风主雨带的精细化结构和台风眼墙极端上升运动特征。.项目研究成果加深了天气尺度波列发展及其发展为台风的本质认识，揭示了季节内热带波动对天气尺度波列和台风生成的调制作用及其可能物理机制，深化认识了台风生成过程中的多尺度相互作用，提高了台风强度和结构精细化认知，获得了热带太平洋气候变迁和跨洋盆相互作用对台风活动气候变化的新认识，为西北太平洋台风生成天气和延伸期预报及其气候预测提供了科学的理论基础，为构建台风生成的延伸期预报模型和气候预测提供了科学依据。