Simulating the Mechanism of the Interannual Variability Mode of the Indian Ocean Sea Surface Temperature Anomalies Impacting on the Summer Rainfall over Eastern China

The ECHAM5 atmospheric general circulation model was used to study how the evolution of the interannual variability mode (IVM) of the Indian Ocean sea surface temperature anomalies (SSTA) from winter to summer influence summer rainfall over eastern China. Observations show that, for positive IVM, the tropical Indian Ocean and the region west of Australia (the west pole) are an anomalous source of water vapor in spring and summer, and provide the water vapor for the region southeast of Madagascar (the east pole) and the continents surrounding the Indian Ocean. In summer, the intensity of Antarctic Oscillation (AAO) over the Indian Ocean region and the Mascarene High increase, whereas the Indian monsoon trough and the South Asia High decrease, which indicates that the Indian summer monsoon circulation weakens. The meridional atmospheric teleconnection of zonal wind anomalies in the Indian Ocean causes westerly anomalies in the tropical Indian Ocean, which depress convective activities over the Maritime Continent but enhance them over the Philippine Sea during summer. This makes the western Pacific subtropical high decrease and shift northeastward. For negative IVM, the observations are the opposite. The model results basically support the abovementioned observations.