夏季西亚与东亚高空西风急流南北偏移的联系及其机理研究

The predominant mode of the summer upper-level westerly jet stream over Asia mainly manifests as the north-south shift (or meridional displacement) of the jet over West Asia and East Asia ("WJMD" and "EJMD" for short). This mode can explain about half the year-to-year variability of the upper-level zonal wind anomalies. Recently, our preliminary results show that WJMD and EJMD have a significant positive relationship with each other, and several factors, including the Silk Road Pattern, may play a role in setting up this linkage. Considering the profound influences of the WJMD and EJMD on the Eurasian climate change, it is of great necessary to delve into the relationship between the WJMD and EJMD. Therefore, all of the analyses of this project will be based on this WJMD-EJMD relationship. We will mainly focus on the following issues: We will reveal the characters of the WJMD-EJMD relationship, including the horizontal and vertical distribution of the circulation anomalies associated with this relationship, and the time evolution of the relationship; Further, we will identify the factors that influence this relationship and explore the underlying physical mechanisms. With respect to these factors, we will give our emphasis on the mid-high latitudinal circulations and the tropical-subtropical SST and convection activities. Results obtained from this project will contribute to a better understanding about the midlatitude circulation changes and their internal physics, facilitating a more accurate interpretation about reasons for the summer Eurasia climate anomalies, and further provide scientific source for construction of "the Silk Road Economic Belt".

夏季亚洲高空西风急流年际变化的主要模态表现为西亚和东亚急流的南北偏移，这一模态能解释高层纬向风年际变率总方差的一半左右。我们最近的初步结果表明，这两者间存在显著的相关关系，丝绸之路遥相关等可能是这种联系得以建立的原因。考虑到西亚和东亚急流的南北偏移对欧亚大陆广大地区气候的重要影响，有必要对西亚和东亚急流年际变化之间的联系进行深入研究。因此，本项目着眼于西亚、东亚急流南北偏移之间的联系，将重点分析这种联系对应的环流特征和时间演变特征，着重从中高纬度环流、热带和副热带海表温度异常及对流活动等方面揭示对这种联系有影响的因子及物理过程。项目的研究结果将有助于我们更好地理解中高纬大气环流异常机理，准确把握夏季欧亚大陆气候异常的形成原因，进而为“一带一路”战略中丝绸之路经济带的建设提供科技支撑。

亚洲高空急流的变化对中高纬度大气环流和气候异常有重要作用，特别是地处西亚和东亚的高空西风急流与丝绸之路波列相关联，对一带一路沿线国家的气候环境变化有较大影响。.该项目以此为背景，使用最近60年NCEP/NCAR和JRA-55等多套逐日和逐月再分析资料以及降水、海表温度等资料，深入研究了夏季西亚、东亚急流年际变化的特征和联系。结果表明这两个区域急流年际变化的主模态都表现为急流位置的南北偏移，且二者具有统计意义上的显著正相关：西亚急流偏北（南）时，东亚急流也更趋向于偏北（南）。有两个因子对两者的紧密联系起重要作用：丝绸之路遥相关和印度半岛-西北太平洋一带的大范围热带降水。该成果为我们理解西亚到东亚之间、以及热带-副热带环流和气候变化的遥相关关系，都提供了参考。.围绕这一研究主题，我们进一步研究了丝绸之路遥相关在不同时间尺度上的变化特征。结果表明：丝绸之路遥相关存在显著的年代际变化，其年代际解释方差可以解释总方差的30%。对比该遥相关型的年际和年代际分量发现：其年际尺度变异对应横跨欧亚大陆上空清晰的波列状环流异常，并导致下垫面类似的波列状冷暖温度异常，年际的遥相关型更符合罗斯贝波理论；而年代际变化对应的环流异常在欧洲和中亚与年际相似，但在东亚明显减弱，且对应的温度异常也北移到俄罗斯远东地区。此外，丝绸之路遥相关还表现出明显的季节内差异：后夏的遥相关型更强、具有明显的位相锁定特征、和北大西洋涛动有显著相关。这部分成果使丝绸之路遥相关的时空图像更加清晰。