Possible Process for Influences of Winter and Spring Indian Ocean SST Anomalies Interannual Variability Mode on Summer Rainfall over Eastern China
冬季和春季印度洋海温异常年际变率模态对中国东部夏季降水的可能影响过程

The thermal conditions of the Indian Ocean is an important factor that can affect the global climate and Asian monsoon variability. Previous studies have paid much more attention to sea surface temperature (SST) variability in the tropical Indian Ocean than the middle-and high-latitude South Indian Ocean, which limits the overall understanding about the Indian Ocean. This study presents the leading mode of the Indian Ocean sea surface temperature anomalies (SSTA) on interannual time scale and the possible process for its influences on summer rainfall over eastern China, ex- pecting to provide a theoretic basis for climate variations research and prediction. The results indicate that the leading mode of the Indian Ocean SSTA on interannual time scale is characterized by southwest-northeast oriented dipole oscil- lation in the subtropical South Indian Ocean. The western pole is located in the southeast of Madagascar and the eastern pole lies in the west of Australia, varying consistently with the tropical Indian Ocean SSTA. Here, the positive (negative) Indian Ocean SSTA interannual variability mode is defined as positive (negative) SSTA in the western pole and negative (positive) SSTA in the eastern pole and the tropical Indian Ocean. The interannual variability mode, which can persist during winter and spring, is significantly negatively correlated with summer rainfall over the middle reach of the Yangtze River (MYR), but significantly positively correlated with rainfall over South China (SC). The possible mechanism can be described as follows: for positive Indian Ocean SSTA interannual variability mode events during winter and spring, the meridional atmospheric teleconnection of zonal wind anomalies in the Indian Ocean leads to westerly anomalies in the tropical Indian Ocean which depress the convective activities over the Maritime Continent in spring and summer. The depressed convective activities make the western Pacific subtropical high weaken and shift northward and eastward, conducing to increased rainfall over SC and reduced rainfall over MYR, and vice versa. Moreover, the Indian Ocean SSTA interannual variability mode can also influence summer rainfall over MYR by changing its water vapor transport stemming from the Indian Ocean and the Bay of Bengal.