Dipole Oscillation in the Southern Indian Ocean and Its Impacts on Climate

Variance and correlation analysis of the Indian Ocean sea surface temperature (SST) indicates that a strong dipole oscillation occurs in the southern Indian Ocean, and then a southern Indian Ocean SST anomalies dipole index (SIODI) is defined. The index in summer and autumn has significant and sustained correlations with the following 500hPa and 100hPa geopotential height anomalies in the tropical regions, which are most significant in winter and next spring and can persist 10 months until the next summer and autumn. The SIODI are closely related to the post-summer rainfall anomalies in China. Corresponding to the positive phase of the SIODI, the western Pacific subtropical high shifts westward and the Tibetan high strengthens and shifts eastward. In addition, Indian and South China Sea summer monsoons weaken, together these anomalous situations lead to more/less rainfall over Yangtze River basin/South China. The reverse occurs during a negative phase scenario. The western Pacific warm pool plays an important role in the relationship between the SIODI and the rainfall anomalies in China. The SIODI seems to be, to a certain extent, independent of ENSO (El Ni˜no-Southern Oscillation).