Understanding the Development of the 2018/19 Central Pacific El Niño

A central Pacific (CP) El Niño event occurred in 2018/19. Previous studies have shown that different mechanisms are responsible for different subtypes of CP El Niño events (CP-I El Niño and CP-II El Niño). By comparing the evolutions of surface winds, ocean temperatures, and heat budgets of the CP-I El Niño, CP-II El Niño, and 2018/19 El Niño, it is illustrated that the subtropical westerly anomalies in the North Pacific, which led to anomalous convergence of Ekman flow and surface warming in the central equatorial Pacific, played an important role in the 2018/19 El Niño event as well as in the CP-II El Niño. Although the off-equatorial forcing played a vital role, it is found that the equatorial forcing acted as a driving (damping) term in boreal spring (summer) of the 2018/19 El Niño. The 2018/19 El Niño provides a timely and vivid example that helps illustrate the proposed mechanism of the CP El Niño, which could be leveraged to improve El Niño predictability.