Abstract
This study explores the response of the Southern Indian Ocean Dipole (SIOD) to the tropical Pacific El Niño‐Southern Oscillation (ENSO) and the underlying mechanisms. Observational analyses reveal a statistically significant correlation ( r = −0.49) between the two modes, which peaks when the Niño3.4 index leads the SIOD index by 2–3 months, indicating a clear guiding role of ENSO. Furthermore, La Niña (El Niño) events exhibit a significant synergistic relationship with positive (negative) SIOD phases during boreal winter (December–January–February, DJF), with both having similar dominant oscillation periods. We elucidate the distinct physical processes through which ENSO influences the SIOD. During La Niña events, an anomalous Walker Circulation triggers upward motion and negative sea level pressure (SLP) anomalies in the northeastern pole of the Positive SIOD (PSIOD). These anomalies, combined with westerly wind anomalies over the tropical Indian Ocean and a localised cyclonic circulation, collectively enhance the spatial structure and the intensity of the sea surface temperature anomalies (SSTAs) associated with the PSIOD. In contrast, El Niño activates the Pacific‐South American (PSA) wave train. Through its modulation of the Southern Annular Mode (SAM), a teleconnection pathway is established that extends into the southern Indian Ocean. Simultaneously, by weakening the Walker Circulation and inducing an anticyclonic circulation, El Niño also modulates the intensity and evolution of the Negative SIOD (NSIOD). Conversely, the development of the NSIOD stimulates northeastward‐propagating Rossby wave trains that provide feedback on ENSO, revealing a bidirectional interaction between the two basins. These multi‐pathway mechanisms have been successfully reproduced by the Community Earth System Model (CESM 1.0.4), validating the complex air‐sea processes connecting ENSO and the SIOD.