四川盆地夏季降水年际变化的主模态分析

利用1979～2018年四川盆地134站夏季降水观测资料、ERA-Interim再分析资料以及英国气象局哈德莱中心的海表温度及海冰资料，对比分析了四川盆地夏季降水异常主模态及其同期大气环流和前期海温海冰演变特征的差异，以探讨其形成机制及前期预测信号。结果表明:四川盆地夏季降水存在两类优势空间模态:全区一致型和东西反相型，在20世纪80年代多出现东西反相型，90年代到21世纪初以一致型为主，进入21世纪10年代后又多表现为东西反相型。不同模态所对应的大气环流和海温海冰的演变具有明显差异，全区一致型降水分布受低纬系统影响显著，在500 hPa高度场上主要表现为西太平洋副热带高压的位置及强度异常；850 hPa风场为辐合或辐散特征，受到来自孟加拉湾、南海、西太平洋三条水汽通道的共同影响，其中与南海水汽通道的相关性最高，一致型降水多/少年水汽在盆地区域南北边界为同收/同支；环流可能受到前期ENSO事件衰减的显著影响。东西反相型降水分布受中高纬环流的影响较大，在500 hPa高度场上的特征类似于极地欧亚型（POL）遥相关；水汽在区域南北边界为一收一支，西多东少型为南收北支，而西少东多型为北收南支，与西太平洋水汽通道关系显著；环流可能受到前期北极海冰异常的影响。

Interannual Variation of the Leading Modes of Summertime Precipitation in the Sichuan Basin

Based on precipitation observation data from 134 stations in the Sichuan Basin, ERA-Interim reanalysis datasets, sea surface temperature (SST), and sea ice datasets from the Met Office Hadley Centre, this study investigates two major modes of summer precipitation over the Sichuan Basin using empirical orthogonal function (EOF) method and linear regression technique. Results showed that the first mode of EOF (EOF1) exhibits a consistent pattern throughout the region, whereas the second mode of EOF (EOF2) exhibits an inverse pattern between the east and west of the Sichuan Basin. In the 1980s, the dominant mode was an east–west reversed pattern, which remained consistent from the 1990s to early 2000s. The inverse pattern has been restored to the dominant position in recent years. Further investigation shows that the EOF1 of precipitation is substantially influenced by the low-latitude circulation in 500-hPa geopotential height, particularly in the western Pacific subtropical high. Convergent or divergent fields control the 850-hPa wind over the basin. The water vapor budget is influenced by water vapor channels in the Bay of Bengal, South China Sea, and western Pacific. The vapor channel in the South China Sea could be crucial. The amount of precipitation of EOF1 corresponds to the consistent input/output of water vapor at the North–South boundary of the Sichuan Basin. The pre-signal for most cases in EOF1 may come from the decaying phase of the El Ni?o–Southern Oscillation. However, the EOF2 is greatly related to the mid and high latitude circulation at 500 hPa, similar to the Polar/Eurasia pattern. The EOF2 mode, which has been found more rain in the west than in the east of the Sichuan Basin, is linked to the input of the southern border and the output of the northern border, and vice versa. The EOF2 pattern is closely related to the water vapor channel in the western Pacific. The variability of Arctic sea ice may be the source of the pre-signal in most EOF2 cases.