ENSO's Response to Volcanism in a Data Assimilation-Based Paleoclimate Reconstruction Over the Common Era

The tropical response to explosive volcanism remains underconstrained in the paleoclimate record. While the atmosphere cools due to aerosol forcing following volcanic eruptions, modeling evidence suggests that the tropical Pacific responds with compensatory warming. Given the rarity of large volcanic eruptions and the short instrumental record, these modeling results require independent verification. Here, we test for links between volcanism and tropical Pacific dynamics using the newly developed Paleo Hydrodynamics Data Assimilation product (PHYDA), which spans the past 2,000 years. Using Pacific sea surface temperature fields from PHYDA and coincident volcanic eruptions, we test the response of the El Nino-Southern Oscillation (ENSO) to large, tropical volcanic eruptions. We identify a weak El Nino-like response of the tropical Pacific in the year following sufficiently large, tropical volcanic eruptions. While the response is not significant at the 95% confidence level using superposed epoch analysis (SEA) and self-organizing maps, a significant result does emerge when employing probability density functions. Our results indicate that the widely used SEA approach, based on composite averaging, may not be sufficiently sensitive to capture an ENSO response in the presence of large internal variability. We additionally conclude that inconsistencies in both the spatial patterns and magnitudes between climate models and PHYDA results indicate that current models overestimate the regional tropical response to volcanic forcing.