Tropical volcanic eruptions and low frequency Indo-Pacific variability drive extreme Indian Ocean dipole events

Abstract

Volcanic eruptions can have significant climate impacts and serve as useful natural experiments for better understanding the effects of abrupt, externally forced climate change. Here, we investigate the Indian Ocean Dipole's (IOD) response to the largest tropical volcanic eruptions of the last millennium. Post-eruption composites show a strong negative IOD developing in the eruption year, and a positive IOD the following year. The IOD and El Niño-Southern Oscillation (ENSO) show a long-term damped oscillatory response that can take up to 8 years to return to pre-eruptive baselines. Moreover, the Interdecadal Pacific Oscillation (IPO) phase at the time of eruption controls the IOD response to intense eruptions, with negative (positive) IPO phasing favoring more negative (positive) IOD values via modulation of the background state of the eastern Indian Ocean thermocline depth. These results have important implications for climate risk in low-likelihood, high-impact scenarios, particularly in vulnerable communities unprepared for IOD and ENSO extremes.