欧亚大陆夏季地表热力异常与同期中国东部夏季降水的可能联系

摘要

Based on ERA-40 reanalysis, CRU TS3.0 dataset, and observational data, the characteristics of Eurasian land surface thermal anomalies in summer and their relationship with summer rainfall in East China were investigated. The results showed that the large-scale characteristics of Eurasian land surface air temperature and sub-surface soil temperature are basically the same. The leading mode of Empirical Orthogonal Function (EOF) manifests characteristics of reversal change between southwest Eurasia and other regions of the continent and the principal components went through transition in the late 1980s. When a positive summer land surface thermal anomaly happens in North India and central-eastern China, the East Asian summer monsoon tends to be strengthened and the western Pacific subtropical high (WPSH) moves eastward, which benefits stronger southerly winds over East China but less water vapor and weakened ascending motion in the Yangtze–Huaihe River basin, resulting in reduced precipitation over this region. At the same time, more water vapor and intensified ascending motion in the southeast and northeast of China tends to produce more summer precipitation, and vice versa. When a positive summer land surface thermal anomaly occurs in the areas to the east and west of Lake Baikal, but a negative anomaly occurs in northeastern China, the East Asian summer monsoon tends to be strengthened and the WPSH moves westward, which results in less water vapor and weakened ascending motion in the southeast of China and central Inner Mongolia, leading to less precipitation over these regions. Meanwhile, more water vapor and intensified ascending motion are found in the rest of East China, accompanied by more precipitation, and vice versa.%利用ERA-40再分析资料、CRU TS3.0数据集以及中国站点观测数据，分析了欧亚大陆夏季地表热力异常的变化特征，在此基础上探讨了我国东部夏季降水与同期欧亚大陆地表热力异常之间的可能联系。研究发现，欧亚大陆地表气温与浅层土壤温度的大尺度变化特征基本一致：经验正交函数分解第一模态空间型表现为大陆西南部分区域与欧亚大陆其他区域反相变化，对应的时间系数均在20世纪80年代末出现转折。当夏季欧亚中纬度印度以北地区和我国中东部地区地表气温偏高时，东亚夏季风的强度偏强，西太平洋副热带高压位置偏东，我国东部偏南风偏强，江淮流域水汽偏少，且气流上升运动偏弱，降水偏少；华南和北方地区水汽偏多，且气流上升运动偏强，降水偏多；反之亦然。当欧亚大陆中高纬贝加尔湖以东及以西地区夏季地表气温偏高，而我国东北部地区夏季地表气温偏低时，东亚夏季风的强度偏强，西太平洋副热带高压位置偏西，我国东南部地区偏南风异常偏强，有利于水汽向江淮流域输送，东南沿海及内蒙古中部水汽偏少，且气流上升运动偏弱，降水偏少；而东部其余地区水汽偏多，且气流上升运动偏强，降水偏多；反之亦然。