On the low‐level circulation over the western north Pacific in relation with the duration of El Niño

We investigate how the low‐level circulation centered at 10°N over the western north Pacific differs between the shorter (SHORT‐E) and longer (LONG‐E) El Niño events based on their duration time. One major difference is the intensity of this circulation. This difference is due to the greater contribution of the 2–3 year quasi‐biennial (QB) signal for the SHORT‐E; strength of the 3–6 year interannual signal is almost the same in a mean sense between the two event types. Further, the amplitude of the QB signal is in phase with that of the interannual signal during the SHORT‐E so that the circulation intensifies and evolves rapidly. The enhanced anticyclonic circulation during the mature stage of SHORT‐E results in shallower thermocline in the equatorial western Pacific, and exerts influence on the duration of the event. During the LONG‐E, the mentioned feature diminishes because of the weak QB. Our analysis further indicates a significant correlation between the zonal SSTA gradient over the Indian Ocean and the intensity of the western north Pacific circulation. A complete understanding of the related mechanism needs further study.