Sub-seasonal impact of El Niño–Southern Oscillation on development of the Indian Ocean Dipole

The Indian Ocean Dipole exhibits large variations in its evolution depending on the presence of El Niño, with notable changes in intensity, duration, and peak phase. Here, using a simple Indian Ocean Dipole model and observational-reanalysis datasets, we revealed that Indian Ocean Dipole events co-evolving with El Niño exhibit an early-summer growth-disruption, which results from a sudden decrease in Indian Ocean Dipole sensitivity to El Niño in May and June, despite the steadily increasing El Niño’s amplitude. In May and June, as the Intertropical Convergence Zone migrates northward with the onset of South Asian monsoon, El Niño-induced low-level cyclonic circulation causes Ekman upwelling over the western Indian Ocean, which stalls Indian Ocean Dipole development. Moist linear baroclinic model experiments verified that the Intertropical Convergence Zone modulates El Niño–Southern Oscillation’s impact on Indian Ocean Dipole seasonally. This study underscores the importance of understanding sub-seasonal dynamics of Indian Ocean Dipole evolution. The Indian Ocean Dipole events co-evolving with El Niño-Southern Oscillation typically have a double peak and a brief pause in early summer due to a sudden decrease in Dipole sensitivity in May and June, attributed to northward rainfall migration, according to analysis of an Indian Ocean Dipole model with observational-reanalysis datasets.