热带外大气季节内振荡与天气涡旋的双向反馈机制研究

Atmospheric circulation in extratropics is featured by the significant intraseasonal oscillation (ISO) with a 20-90d period which is an important predictability source of subseasonal-to-seasonal forecasting. Therefore, it is a key issue to study mechanisms of the extratropical ISO. This project will propose a research on the two-way feedback mechanism between the extratropical ISO and synoptic-scale eddy with a 2-8d period to explain the main characteristics during development and propagation of the extratropical ISO. This proposal aims to reveal key features and mechanisms of the feedback between the extratropical ISO and synoptic eddy employing the approaches including data diagnosis, theoretical analysis, and model experiments. Research will include the contents as follows. Features of eddy feedback statistics and synoptic eddy structure change will be first examined for canonical patterns of the extratropical ISO in boreal winter. Physical mechanism for feedback of synoptic eddy onto development and propagation of the ISO patterns will be then studied. Quantitative diagnostics will be proposed to measure contributions of the eddy feedbacks to the growth and propagation of the ISO. Modulations of mean flow and then baroclinicity variations associated with development and evolution of the ISO to synoptic eddy activity, and their feedback on the ISO itself will also be examined. Finally, a schematic diagram for depicting the closed two-way feedback mechanism between the extratropical ISO and synoptic eddy will be set up. Through this project, it will be expected to increase understanding of mechanisms of the development and evolution of the extratropical ISO phenomenon.

热带外大气环流中存在着显著的20-90天尺度季节内振荡（ISO），是开展次季节-季节（S2S）预报的重要物理基础，研究热带外ISO机制问题一直是学界关注的重点。本项目拟对热带外大气ISO与天气尺度涡旋（2-8天）的双向反馈机制开展研究，以试图解释热带外ISO发展和传播的主要特征。本研究着眼于热带外ISO与天气涡旋双向反馈的特征和机理问题，通过资料诊断、理论分析和数值试验等手段，考察与北半球冬季热带外ISO典型模态相关联的涡旋反馈统计量特征和天气涡旋结构变化特征，研究天气涡旋对ISO模态自身发展和传播特性进行反馈作用的物理机制，发展用于度量涡旋反馈对ISO增长和传播贡献的定量化指标，并考察ISO发展演变过程中相伴随的基本流以及斜压性改变对天气涡旋活动的调制及反馈作用，从而构建热带外大气ISO与天气涡旋之间闭合的双向反馈机制概念模型。通过本项目研究，有望提升对热带外ISO发展演变机制的认识。

热带外大气环流中存在着显著的20-90天尺度季节内振荡（Intra-Seasonal Oscillation, ISO），是开展次季节-季节预报的重要物理基础，研究热带外ISO机制问题一直是学界关注的重点。本项目深入研究了天气涡旋对热带外不同区域ISO的反馈特征和机制。主要研究成果如下：.1）理论分析了涡旋强迫统计量与ISO之间的时空变化关系，并通过资料诊断进行了证实；明确了与北大西洋涛动（North Atlantic Oscillation, NAO）、太平洋-北美型相关联的天气涡旋动力、热力反馈特征以及涡旋反馈对上述热带外ISO主模态发生、发展和传播特性的影响。.2）运用天气涡旋结构分解法，揭示了不同典型空间形态的ISO对天气涡旋结构的运动学调制特征以及由此引起的涡旋动力、热力反馈的运动学机制；并运用线性斜压模式开展敏感性试验进一步验证上述机制；最终构建了热带外大气ISO与天气涡旋之间双向反馈机制的概念模型。.3）发展了用于测度涡旋反馈对ISO增长所做贡献的定量化指标，考察了该指标在涡旋动力、热力以及二者综合反馈情形下的时空特征。.4）对非线性模式模拟的ISO和涡旋反馈统计量进行了评估，以考察模式性能，为模式发展提供参考信息。.5）针对观测中季节内NAO的位相不对称特征，运用涡旋反馈贡献的定量化指标为其提供了动力学和热力学角度的成因解释；并将NAO发展演变过程中伴随的斜压性和涡旋活动性改变与前文的正压运动学机制相结合，进一步阐述了NAO位相不对称性的成因。.项目资助培养了博士2名、硕士6名。项目负责人入选中组部“万人计划”青年拔尖人才、气象高层次科技创新人才计划“气象领军人才”，获得气象科学技术进步二等奖、十佳全国优秀青年气象科技工作者。由课题资助发表的正式期刊文章21篇，其中包括SCI级论文20篇。

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