Volcanic Eruptions Impact Key Atmospheric and Oceanic Parameters Across ENSO States

El Niño Southern Oscillation (ENSO) is a tropical Pacific climate system fluctuation representing Earth's strongest year-to-year climate variations. The influence of volcanic eruptions on ENSO and the effects of ENSO background states on climate responses were analyzed using GISS Model E2.1 simulations. A volc-pinatubo-full procedure from VolMIP with an eruption in the sixth month simulated an explosion case. Parameter responses were evaluated using anomalies from the control period calculated using the difference between perturbed and control simulations. Simple linear regression analysis was performed using a Niño-3.4 index, and a multivariable regression was conducted for atmosphere-ocean carbon flux and seven marine variables. Results suggested that different climate variables respond differently based on geographic regions and ENSO states in the presence of a volcanic eruption. Globally, more CO2 was going into the ocean with increasing volcanic forcing magnitude, with most CO2 uptake happening during a La Niña. Regionally, the Tropical Pacific Ocean absorbed more CO2 after a 3x Pinatubo-sized eruption in both an ENSO+ (El Niño) and ENSO- (La Niña) initial state. Multivariable regressions showed correlations between various marine variables that differ across different regions and ENSO states. Post-eruption, the surface air temperature was also shown to vary in different regions in different coastal regions. The ITCZ (intertropical convergence zone) experienced reduced rainfall post-eruption, most noticeable over Africa. Overall, our model showed no evidence of volcanic eruptions triggering an ENSO event.