Contrasting SST anomalies over the Indian Ocean between the two types of El Niño events during boreal autumn

The present work investigates the different impacts of sea surface temperature (SST) anomalies over the tropical Indian Ocean as associated with two types of El Niño events during boreal autumn, based on the observed data sets from 1951 to 2010. Here, we focus on the relationship between the Indian Ocean Dipole (IOD) and these two types of El Niño. It is shown that the positive IOD-like SST anomaly occurs for both EP and CP El Niño autumns, but with a different probability. Most of EP El Niño events are accompanied by a strong positive IOD-like SST anomaly. However, a weak positive IOD-like SST anomaly appears for only half of the CP El Niño events. It seems that there is a strong relationship between the intensity of IOD and that of EP El Niño. That is, IOD tends to occur during the strong EP El Niño autumns, with a strong sinking current and negative rainfall anomaly over the maritime continent. During the CP El Niño, however, the occurrence of IOD seems to be unrelated with the strength of CP El Niño. The location of the CP El Niño is a possible key effect on the intensity of IOD in autumn. For the CP El Niño autumns when an obvious IOD appears, the warming SST anomaly is located slightly eastward over the central Pacific with a strong sinking current and severe drought over the maritime continent, as well as a significant easterly anomaly over the tropical Indian Ocean. While in the CP El Niño autumns during which no positive IOD-like SST anomaly occurs, the Pacific warming SST anomaly is located relatively further west. The very weak anomalous sinking motion seems limited help to sustain the SST anomaly over the Indian Ocean.