东亚西风急流协同变化与我国东部降水异常的关系及其机理

The variations of the location, shape and intensity of the East Asian Subtropical Westerly Jet (EASWJ) have an important significance of local weather and climate. This project intends to study the collaborative variation between the east-west and north-south position of the EASWJ during rainy seasons, and its relationship with weather and climate anomalies in China and its possible mechanism. By the using of the United States National Center for environmental prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and station observational precipitation data in China, the collaborative variation of the EASWJ in different height is analyzed, including the manifestation, seasons and interannual variation characteristics and its relationship with precipitation anomaly in East Asia. With the statistical methods, such as composite, correlation analysis and linear regression, the important impact of the collaborative variation of the EASWJ in season and interannual scales on the precipitation anomaly over eastern China during flood season is investigated, and revealed its weather and climate significance. From the Land and sea thermal contrast and Tibetan Plateau heating heterogeneity, and by the using of the Maximum Covariance Method and Generalized Equilibrium Feedback Analysis, the underlying surface thermal difference during rainy season impacts on the collaborative change of the EASWJ. Using the dynamic analysis and numerical model simulation, the possible mechanism of east-west and north-south position of collaborative variation of the EASWJ is discussed. The research result will help deepen the understanding of collaborative changes on the different levels of the EASWJ.

东亚副热带高空西风急流位置、形态和强度变化具有重要的天气气候学意义。本项目拟研究汛期东亚副热带西风急流东西和南北协同变化规律，分析其与中国天气气候异常的关系及其可能机制。利用NCEP/NCAR再分析资料和中国台站降水观测资料，分析东亚副热带西风急流东西和南北协同变化在不同高度上的表现形式、季节和年际变化特征，研究西风急流协同变化与东亚降水异常的关系。利用合成、相关分析和线性回归等统计方法，研究对中国东部汛期降水异常有重要影响的西风急流东西和南北协同变化的季节和年际变化规律，并揭示其天气气候学意义。从海陆热力差异和青藏高原加热非均匀性的角度用最大协方差法和广义平衡反馈分析法，研究汛期下垫面热力差异对东亚西风急流东西和南北协同变化的作用。利用动力学分析和数值模式模拟，研究汛期东亚副热带西风急流东西和南北协同变化的可能机制。研究成果将有利于加深对东亚副热带西风急流位置协同变化规律的认识。

东亚副热带高空西风急流位置、形态和强度变化具有重要的天气气候学意义。本项目研究了汛期东亚副热带西风急流东西和南北协同变化律，分析其与中国天气气候异常的关系及其可能机制。研究结果表明：1）东亚副热带西风急流出口区极强的纬向风异常变率预示着东亚副热带西风急流两种分布类型：向东伸展的强急流型和向西收缩的弱急流型。中纬度雨带和热带辐合区在急流东伸时比弱急流西缩时位置偏东和偏南。强、弱急流型更多可能发生在ENSO衰减阶段。在强El Nino冬季非绝热加热和向外长波辐射呈三极子异常型对急流东伸型的形成起着重要作用。这种三极子异常型空间分布使得太平洋的Hadley环流加强且也常出现在弱的El Nino期。而弱急流型时则无此三极子异常型。2）夏季在北半球高层200hPa纬向风异常存在两个主要模态：南北偶极子结构（M1）和在亚洲大陆上四分之一偶极子结构(M2), M1代表亚洲副热带西风急流的经向移动，M2代表西风急流的东北 - 西南倾斜。功率谱分析表明，M1模态具有4.9年的显著周期，而M2模态具有3.6和7.7年的显著周期。与两种模态相对应的大气环流具有准正压结构及其对应的中国降水分别为南北型和东西偶子型。M1型出现在El Nino发展阶段，而M2型则发生在La Nina衰减期。基于观测事实和AGCM敏感试验验证了西风急流这两种型形成的可能物理机理。在中纬度太平洋异常冷海温和热带印度洋和太平洋暖海温是主要驱动M1型的形成。在热带印度洋和太平洋海温异常引起了对流层上层南北温度偶极子的响应。El Nino加热在热带引起对流层温度暖异常，中纬度冷海温异常导致对流层温度冷异常。M2型的形成分为两部分：东部和西部。东部对流层上层反气旋涡度异常主要是受当地北太平洋海温冷异常作用，而西部的气旋异常主要是来自于北大西洋向东亚传播的Rossby波列的作用。