The Weakening of the Lagged Relationship between the Indian Ocean Basin Mode and Central Pacific ENSO in Recent Decades: Influence of the Tropical Atlantic Ocean

Abstract The present study examines the interdecadal variability in the lagged relationship between the Indian Ocean Basin (IOB) and central Pacific (CP) ENSO events in recent decades via observational data and phase 6 of the Coupled Model Intercomparison Project (CMIP6) model data. It is found that the teleconnection between the winter-to-spring IOB and CP ENSO a year later has changed since 2000. Prior to 2000, IOB warming (cooling) triggered CP La Niña (El Niño) through wind anomalies over the Indo-Pacific. However, the interbasin connection between the IOB and CP ENSO weakened after 2000 owing to the weak linkage between the IOB and zonal wind anomalies in the tropical western Pacific. Furthermore, sea surface temperature anomalies (SSTAs) in the tropical Atlantic Ocean (TAO) could play a crucial role in the interdecadal variability of the IOB–CP ENSO relationship. Prior to 2000, the tropical Atlantic and Indian Oceans were coupled. The covariability between the IOB and TAO SSTAs has led to an increase in CP ENSO intensity in the ensuing seasons by surface wind variation over the tropical western Pacific. However, after 2000, the tropical Atlantic and Indian Oceans were decoupled, with a weakening contribution to surface wind variation in the western Pacific, resulting in the weakening of the IOB–CP ENSO relationship. These findings are corroborated by CMIP6 model simulations. Significance Statement While the boreal winter-to-spring Indian Ocean Basin (IOB) contributes to the occurrence of central Pacific (CP) ENSO a year later, it remains unclear whether this predictor of CP ENSO has varied over time in recent decades. Moreover, it is uncertain whether a close relationship exists between the sea surface temperature anomalies (SSTAs) in the Atlantic Ocean and the interdecadal variability in the IOB–CP ENSO relationship. This study aims to understand the interdecadal variability in the connection between the IOB and CP ENSO after 1979, as well as the influence of the tropical Atlantic Ocean (TAO). Our analysis demonstrated that the lagged relationship between the IOB and CP ENSO has weakened since 2000. Furthermore, we discovered a close relationship between the SSTAs in the TAO and the interdecadal modulation of the IOB–CP ENSO relationship. These findings emphasize the significance of three-ocean interactions in the interdecadal variability of ENSO prediction.