近40年夏季热带中太平洋海温对东亚气候影响的不对称性

The Asymmetry of the Influence of Sea Surface Temperature in the Tropical Central Pacific on the Climate in East Asia in the Past 40 Summers

摘要: 基于1980~2020年CRU、NCEP/NCAR再分析资料等数据，本研究系统分析了夏季热带中太平洋海温异常对于同期东亚气候的调控作用，重点探讨了该影响的不对称性特征及可能的物理机制。通过经验正交函数分解、合成分析、线性回归与T检验等方法，探讨了热带太平洋海温的主要模态及年际变化趋势，并利用统计方法和动力诊断进一步分析了其对东亚气候的影响。结果显示：热带中太平洋海温在近40年时间里持续增暖，中部型厄尔尼诺事件频发，海温暖位相对东亚夏季降水与气温的分布影响强于冷位相，表现为典型的非对称性响应。偏暖年份，西太副高北抬，驱动华南沿岸、长江中下游及东北地区降水增多，中纬度减少，中高纬度呈现“西伯利亚增暖——鄂霍茨克海降温”偶极型；偏冷年副高偏弱位置偏南，响应偏弱，局地性显著，机制上表现为对流位置偏西、热力强迫减弱及遥相关波列激发能力减弱。大气环流和辐射场分析结果表明，海温冷暖位相通过调控热带对流中心位置及沃克环流强度，引发高层南亚高压位置、中层鄂霍茨克海海低涡活动，副高位置变动、低层水汽输送路径，热力强迫差异，对东亚气候产生了显著的非对称性影响。本文为理解ENSO多样化背景下的区域气候异常机制提供了科学依据，有利于提升东亚地区的夏季气候预测能力。

Abstract: Based on multi-source data such as CRU and NCEP/NCAR reanalysis data from 1980 to 2020, this paper systematically analyzed the regulatory effect of summer tropical central Pacific Sea surface temperature (SST) anomalies on the climate of East Asia during the same period, with a focus on the asymmetry characteristics of this influence and its possible physical mechanisms. Through methods such as empirical orthogonal function decomposition, composite analysis, linear regression, and t-test, the main modes and interannual variation trends of SST over the central tropical Pacific were identified. By using a fixed standard deviation threshold to distinguish significantly warm and cold years, further comparative analysis revealed that the SST in the Nino4 region has been continuously warming over the past 40 years, with frequent occurrences of central El Niño. The warm phase of the SST has a much stronger impact on the distribution of summer precipitation and temperature in East Asia than the cold phase, showing a typical asymmetric response. During warm years, the Western Pacific subtropical high shifts northward, driving increased precipitation along the coast of South China, in the middle and lower reaches of the Yangtze River, and in Northeast China, while precipitation decreases in the mid-latitudes. In the mid-high latitudes, a dipole pattern of warming in Siberia and cooling in the Sea of Okhotsk emerges. During cold years, the subtropical high is weaker and located further south, with a weaker response and more local characteristics. Mechanistically, this is manifested as a westward shift of the convection position, weakened thermal forcing, and reduced ability to excite teleconnection wave trains. Further analysis of the atmospheric circulation and radiation indicated that the warm and cold phases of the SST regulate the position of the tropical convection center and the intensity of the Walker circulation, thereby influencing the position of the upper-level South Asian High, the activity of the mid-level Okhotsk Sea low vortex, the position of the subtropical high, the low-level water vapor transport path, and the thermal forcing difference, exerting significant asymmetric impacts on the climate of East Asia. This study provides a scientific basis for understanding the regional climate anomaly mechanisms under the background of diverse ENSO and is conducive to improving the ability to predict summer climates in East Asia.