Quantifying the role of tropical Indian Ocean observations to central Pacific El Niño prediction

Abstract Over the past two decades, forecasting the El Niño–Southern Oscillation has become increasingly challenging, primarily due to the inherent difficulty in predicting Central Pacific (CP) El Niño events. In this study, we present a detailed analysis by explicitly quantifying the role of the tropical Indian Ocean (IO) on the initial uncertainty of CP-El Niño predictions. We identify optimal observation sites within the tropical IO that significantly reduce this uncertainty and validate their efficacy through observing system simulation experiments within a fully coupled climate prediction system. Our results demonstrate a remarkable achievement in the root mean squared errors of the prediction initial conditions using Community Earth System Model. This study not only enriches our understanding of the interplay between the tropical IO and CP-El Niño but also offers a concrete strategy for enhancing CP-El Niño forecasts, advancing seasonal prediction capabilities, and bolstering global resilience against the escalating frequency of CP-El Niño events.