Effects of volcanism on tropical variability

The effects of large tropical volcanic eruptions on Indo-Pacific tropical variability are investigated using 122 historical ensemble members from the Coupled Model Intercomparison Project 5. Radiative forcing due to volcanic aerosols in the stratosphere is found to increase the likelihood of a model climatic response that projects onto both the El Niño-Southern Oscillation and the Indian Ocean Dipole (IOD). Large eruptions are associated with co-occurring El Niño and positive IOD events in the ensemble means that peak 6-12 months after the volcanic forcing peaks, marking a significant increase in the likelihood of each event occurring in the Southern Hemisphere (SH) spring/summer posteruption. There is also an ensemble mean La Niña-like response in the third SH summer posteruption, which coincides with a significant increase in the likelihood of a La Niña occurring. Taken together with the initial cooling, this La Niña-like response may increase the persistence of the cool global average surface temperature anomaly after an eruption.