Revisiting the Mechanisms of ENSO Response to Tropical Volcanic Eruptions

Stratospheric volcanic aerosol can have major impacts on global climate. Despite a consensus among studies on an El Niño-like response in the first or second post-eruption year, the mechanisms that trigger a change in the state of El Niño-Southern Oscillation (ENSO) following volcanic eruptions are still debated. Here, we shed light on the processes that govern the ENSO response to tropical volcanic eruptions through a series of sensitivity experiments with an Earth System Model where a uniform stratospheric volcanic aerosol loading is imposed over different parts of the tropics. Three tropical mechanisms are tested: the “ocean dynamical thermostat” (ODT); the cooling of the Maritime Continent; and the cooling of tropical northern Africa (NAFR). We find that the NAFR mechanism plays the largest role, while the ODT mechanism is absent in our simulations as La Niña-like rather than El-Niño-like conditions develop following a uniform radiative forcing over the equatorial Pacific.