Different influences of two types of El Nios on the Indian Ocean SST variations

By comparing correlation of sea surface temperature (SST) and vertical circulation with canonical El Nio and El Nio Modoki, we find that El Nio Modoki has an effect on the Indian Ocean different from traditional El Nio. There exists obvious Indian Ocean basin mode (IOBM) after canonical El Nio, while insignificant SST anomalies exist in the Indian Ocean after El Nio Modoki. Anomalous downdraft and updraft appear over the eastern and western Indian Ocean, respectively, during canonical El Nio, while anomalous updraft is weak over the Indian Ocean during El Nio Modoki. Besides, the strength of El Nio Modoki is slightly weaker than that of canonical El Nio. According to previous studies, two mechanisms can explain IOBM after canonical El Nio: tropospheric temperature (TT) mechanism and ocean dynamics. However, both of them do not exist during El Nio Modoki. Comparing with the complicated oceanic processes, it is convenient to verify the observed TT anomalies and test the possible mechanism using the simple model. Therefore, we pay more attention on the question why TT mechanism does not work during El Nio Modoki. Using a linear barocinic model (LBM), we demonstrate that the strength of SST anomalies and cold SST anomalies in the eastern Pacific have an influence on TT anomalies. Especially, cold SST anomalies in the eastern Pacific cancel the effects of warm SST anomalies in the central Pacific on TT anomalies. It suggests that the SST anomalies in the eastern Pacific are important for the TT mechanism in two types of El Nio.