Decadal Variability of the Lagged IOD–ENSO Relationship in CMIP6 Models

The Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) are two major modes of interannual climate variability that interact across the Indo-Pacific region. Although the autumn IOD is known to influence ENSO with a lag of about one year, the decadal stability of this relationship remains poorly understood. Here we investigate the decadal variability of the lagged IOD–ENSO relationship using observations and 30 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Observational analyses reveal pronounced non-stationarity in the lagged IOD-ENSO linkage, characterized by a stronger (weaker) relationship during the negative (positive) phase of the Atlantic Multidecadal Oscillation (AMO). CMIP6 models exhibit a wide spread in their ability to reproduce this behavior, with only a subset capturing the observed decadal modulation. The inter-model differences are consistent with variations in the simulated amplitude of AMO variability. Models with more realistic AMO variability tend to better reproduce the observed decadal variability of the lagged IOD-ENSO linkage. These results suggest that AMO variability may be one contributing factor to the modulation of the lagged IOD–ENSO relationship, with potential implications for ENSO prediction.