Contrasting seasonal evolution features of Indian Ocean Dipole accompanied with two-type El Nino

The differences in the seasonal evolution features of Indian Ocean Dipole( IOD) accompanied with two-type El Nino have been investigated based on the observed dataset from 1951 to 2012. Here,this paper focuses on the ocean-atmosphere coupled processes over the tropical Indian Ocean during the evolution of IOD. Results show that,when IOD peaks,the intensity and location of the warming SST anomalies( SSTAs) are different between the IOD co-occurred with EP and CP El Nino. When IOD peaks during EP El Nino,tropical northwestern Indian Ocean warms up and the equatorial southeastern Indian Ocean cools off with a similar intensity,associated with a strong anomalous Walker circulation rising over the western Indian Ocean and sinking over the Maritime Continent. But the warm SSTA locates southward over the central Indian Ocean at the peak of the IOD during CP El Nino,associated with weaker anomalous rising over central Indian Ocean. As to the seasonal evolution of the IOD co-occurred with EP El Nino,the warm and cool SSTAs develop intensely in summer then peak in autumn,which is resulted from the weak southwest summer monsoon over western Indian Ocean and the strong anomalous easterly over eastern Indian Ocean. By comparison,the evolution of IOD during CP El Nino is associated with the strong anomalous easterly over eastern Indian Ocean and anomalous negative vorticity winds in the low troposphere over the central Indian Ocean. The dipole SSTA develops when the west pole of the triple pattern SSTA decays,which is different from the IOD co-occurred with EP El Nino.