东亚夏季风环流的齿轮耦合模态年际变化对中国降水多样性的影响

The East Asian summer monsoon (EASM) plays a very import role in the variations of summer rainfall in China. Evidences suggest that the west North Pacific subtropical high (WNPSH), the south Asian high (SAH), and the Mongolian cyclone (MC) are three important dynamic wheels of EASM, their complex interactions on interannual time scales may modulate the intensity of EASM, the moist transporting paths, and the front of cold-warm air interaction, thereby give rise to the interannual diversity of rainfall in China. A number of studies suggest that the vary modes of the EASM circulation is not only related to the interannual variability of the tropical air-sea interaction, but also influenced by the mid-latitude counterpart. However, how to reveal the joint and independent impact of tropical and mid-latitude air-sea interactions, and what is their different impact on the diversity of EASM and summer rainfall in China have not clearly addressed in the previous studies. In this regard, we intend to discuss (1) the interannual multi-modes of summer rainfall in China and its time stability; (2) the relationship between the coupling wheels of EASM and the diversity of rainfall in China, and (3) the possible joint impacts of tropical and mid-latitudes air-sea interactions on the multi-modes of EASM and rainfall on interannual time scale. In this project, we will propose a time-phase EOF (T-EOF) analysis method, and apply this technology to isolate the joint and independent impact of tropical and mid-latitude air-sea interactions. On the basis of data analyses and numerical modeling, we will reveal the physical mechanism behind the interannual diversity of EASM and rainfall in China from the joint impacts of global scale air-sea interactions, and provide some helpful suggestions for the summer monsoon rainfall forecast.

东亚夏季风是影响中国夏季降水的最重要季风系统，环流成员之间存在相互作用。西太平洋副热带高压，南亚高压和蒙古气旋是东亚夏季风环流的主要驱动力和东亚夏季风环流"齿轮耦合"模态的三个重要成员，而齿轮耦合模态的年际变化与中国夏季降水模态的多样性存在密切的关联。其中，热带和中纬度海-气相互作用的协同和相对独立影响很可能是导致东亚夏季风环流齿轮耦合多模态的重要成因。为此，本项目将重点研究如下科学问题：（1）中国夏季降水年际变化的多模态特征及其时间稳定性；（2）东亚夏季风环流多齿轮耦合及其与中国夏季降水多样性关系；（3）热带和中纬度海-气相互作用协同变化对东亚夏季风年际变化影响。本项目将提出和采用相空间经验正交分解（T-EOF）方法，分离热带和中纬度海-气相互作用的协同和独立影响，同时结合资料统计和数值模拟方法，揭示东亚夏季风多齿轮耦合模态和中国夏季降水多样性变化机理。

基于东亚夏季风的三维环流结构和中国副热带锋面降水的特点，本项目探讨了西太副高、南亚高压和蒙古气旋这三个最重要的环流成员在次季节至季节尺度上的齿轮耦合模态变化，及其对中国夏季降水年际变化多样性的影响，揭示了热带太平洋、印度洋和北大西洋海温协同变化对东亚夏季风环流齿轮和中国夏季降水的多模态变化机理。此外，我们将研究范围扩展到冬季，探讨了北极增暖、ENSO等对东亚冬季风次季节至季节尺度变化机理。取得的主要成果有：（1）揭示了东亚夏季风季节进程中南亚高压与西太副高之间的垂直齿轮耦合对南海夏季风的爆发的先兆影响和物理机理，指出了南亚高压、西太副高和蒙古气旋在次季节尺度耦合多模态特征，及其推动中国夏季雨带由南向北推进中的作用；（2）提出了蒙古气旋和南亚高压，以及西太副高和南亚高压两种不同齿轮耦合模态对东亚夏季风和中国夏季雨带的影响，揭示了热带太平洋、印度洋和北大西洋海温协同变化对中国夏季降水年际变化多样性的影响和机理；（3）提出了北极增暖通过加强大气内部变率对东亚冬季极端气温冷暖两极化的影响机理，揭示了超级ENSO事件背景下华南次季节尺度降水对季节降水异常的重要贡献。上述部分研究成果被应用于中国夏季降水预测会商和决策服务中，提供了重要的科学理论参考。本项目发表论文24篇，其中SCI论文15篇，培养硕士和博士研究生7人。