Influence of the IOD on the relationship between El Niño Modoki and the East Asian‐western North Pacific summer monsoon

The relationship between El Niño Modoki and the East Asian‐western North Pacific summer monsoon ( EA‐WNPSM ) has been revealed to be under the influence of Indian Ocean Dipole ( IOD ). When a pure El Niño Modoki occurs without a positive IOD , a strong EA‐WNPSM is observed with a significant anomalous low‐level cyclone over the western North Pacific ( WNP ), excessive rainfall there and deficient Meiyu–Baiu rainfall. In contrast, when an El Niño Modoki happens simultaneously with a positive IOD , the anomalous EA‐WNPSM tends to be much weaker. This difference is attributed to a positive IOD effect. The results demonstrate that a positive IOD usually leads to a strong South Asian summer monsoon heating, which further causes easterly anomalies in the western Pacific. These anomalous easterlies tend to strengthen the WNP anticyclonic vorticity leading to a weak EA‐WNPSM . Therefore, a positive IOD weakens the relationship between the El Niño Modoki and the EA‐WNPSM . In addition, numerical experiments verified that the strong low‐level WNP cyclonic anomaly is built through the off‐equatorial heating associated with the local cyclonic circulation. The anomalous WNP anticyclonic vorticity induced by a positive IOD weakens this off‐equatorial heating, thus leading to a weak EA‐WNPSM .