Interdecadal change in the relationship between the boreal winter North Pacific Oscillation and the following summer El Niño

The boreal winter North Pacific Oscillation (NPO) has a significant impact on the tropical Pacific large scale air-sea interaction in the following spring and summer. But it is unclear whether the boreal winter NPO is associated with the El Niño development or decaying during following summer. This study confirms the relationship between the winter NPO-like sea level pressure anomalies and following summertime El Niño and reveals an interdecadal change in this relationship. It tends to promote the development of sea surface temperature anomaly in central equatorial Pacific in the following summer when the subtropical lobe of the NPO located west of its average position. But after a significant eastward shift of NPO’s subtropical lobe, it is more conducive to the development of sea surface temperature anomaly in eastern equatorial Pacific. The eastward shift of the NPO’s subtropical lobe altered both the seasonal foortprint mechanism and the trade wind charging mechanism associated with the NPO, thus profoundly influenced the summertime El Niño. The findings in the present study have implications for a better understanding of the relationship between the boreal winter NPO and the El Niño in developing summer.