Tropical explosive volcanic eruptions can trigger El Niño by cooling tropical Africa.

TLDR: It is shown that an El Niño tends to peak during the year following large eruptions in simulations of the Fifth Coupled Model Intercomparison Project (CMIP5), and that a Pinatubo-like eruption cools tropical Africa and drives westerly wind anomalies in the Pacific favouring anEl Niño response.

Abstract: Stratospheric aerosols from large tropical explosive volcanic eruptions backscatter shortwave radiation and reduce the global mean surface temperature. Observations suggest that they also favour an El Nino within 2 years following the eruption. Modelling studies have, however, so far reached no consensus on either the sign or physical mechanism of El Nino response to volcanism. Here we show that an El Nino tends to peak during the year following large eruptions in simulations of the Fifth Coupled Model Intercomparison Project (CMIP5). Targeted climate model simulations further emphasize that Pinatubo-like eruptions tend to shorten La Ninas, lengthen El Ninos and induce anomalous warming when occurring during neutral states. Volcanically induced cooling in tropical Africa weakens the West African monsoon, and the resulting atmospheric Kelvin wave drives equatorial westerly wind anomalies over the western Pacific. This wind anomaly is further amplified by air-sea interactions in the Pacific, favouring an El Nino-like response.El Nino tends to follow 2 years after volcanic eruptions, but the physical mechanism behind this phenomenon is unclear. Here the authors use model simulations to show that a Pinatubo-like eruption cools tropical Africa and drives westerly wind anomalies in the Pacific favouring an El Nino response.