Mechanisms of ENSO Sensitivity to Volcanic Forcing and Atmospheric Noise
Abstract
Stratovolcanic eruptions are known to impact El Niño-Southern Oscillation (ENSO), one of the most powerful climate variability modes on Earth. The aerosol plume formed after such eruptions spreads globally in the lower stratosphere affecting the radiative balance of the planet. The redistribution of radiative heating causes complex dynamical responses, which observational and modeling studies suggest favor anomalous warming of the Pacific in the first year or two after an eruption.
We simulated climate impacts of volcanic eruptions of different magnitudes using the GFDL CM2.1 global coupled GCM, to better understand the physical mechanisms affecting ENSO. In our experiments, the ENSO cycle is found to be sensitive to the seasonal timing of the eruption, to the preconditioning of tropical Pacific subsurface temperatures, to model biases in simulating ENSO, and even to atmospheric noise which broadens the distribution of possible ENSO responses. To obtain statistically significant results, we conducted 100-member ensemble simulations spanning multiple types of initial conditions, representing a total of over 16,000 years of simulation. We find that the ENSO response to a volcanic eruption comprises both stochastic and deterministic components. The stochastic component, defined as the response induced by tiny perturbations, is the strongest for eruptions occurring in boreal winter or spring, consistent with the spring "predictability barrier" for ENSO. In contrast, the deterministic response scales with the magnitude of volcanic forcing and emerges more clearly from the stochastic response for eruptions that occur after boreal spring. The main drivers of the ENSO response are the equatorial Pacific ocean dynamical thermostat, and wind changes arising from increased land-ocean temperature gradients, with the former driver being more prolonged and essential than the latter.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGC13E1064P
- Keywords:
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- 0370 Volcanic effects;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 4313 Extreme events;
- NATURAL HAZARDSDE: 8408 Volcano/climate interactions;
- VOLCANOLOGYDE: 8409 Atmospheric effects;
- VOLCANOLOGY