Abstract
Proxy-based reconstructions of the past suggest that the Pacific ocean has often shown El Niño-like warming after low-latitude volcanic eruptions, while climate model simulations have suggested diverse responses. Here we present simulations from a coupled ocean–atmosphere model that illuminate the roles of ocean preconditioning, eruption magnitude and timing, and air–sea feedbacks in the El Niño/Southern Oscillation (ENSO) response to these eruptions. A deterministic component of the response, which dominates for boreal summer eruptions, leads to cooler tropical Pacific sea surface temperatures in the eruption year and El Niño-like warming the following year. A stochastic component is also important, especially for boreal winter eruptions. The simulated ENSO response depends nonlinearly on the eruption magnitude and the tropical Pacific conditions before the eruption. We conclude that adequate sampling is critical to accurately assess the ENSO responses in both models and observations.
Highlights
Proxy-based reconstructions of the past suggest that the Pacific ocean has often shown El Niño-like warming after low-latitude volcanic eruptions, while climate model simulations have suggested diverse responses
The deterministic impact—characterized by cooling of the tropical Pacific in the first year after the eruption, followed by El Niño-like warming in the second year—is clearest for June eruptions, while for February eruptions it is obscured by effects of stochastic westerly wind events in the west Pacific during boreal spring
We find that the deterministic responses to April and June eruptions increase with the magnitude of the volcanic aerosol forcing; tripling the eruption magnitude does not triple the Pacific response, and the increase strongly depends on the ocean preconditioning
Summary
Proxy-based reconstructions of the past suggest that the Pacific ocean has often shown El Niño-like warming after low-latitude volcanic eruptions, while climate model simulations have suggested diverse responses. We present simulations from a coupled ocean–atmosphere model that illuminate the roles of ocean preconditioning, eruption magnitude and timing, and air–sea feedbacks in the El Niño/Southern Oscillation (ENSO) response to these eruptions. A deterministic component of the response, which dominates for boreal summer eruptions, leads to cooler tropical Pacific sea surface temperatures in the eruption year and El Niño-like warming the following year. ENSO is a coupled atmosphere-ocean phenomenon describing the anomalous change of trade winds and sea surface temperature (SST) in the equatorial Pacific. CP and EP El Niños involve different physical processes and affect global climate differently[14,15]. Strong volcanic eruptions can suddenly disrupt ENSO on a short time scale (2–5 years) and may serve as a natural experiment in helping to illuminate the mechanisms of ENSO’s sensitivities to external forcings[30,31,32,33,34]
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