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arXiv · 2608.26767

Detectability of Forced ENSO Changes under Global Warming: Insights from the Recharge Oscillator

Sooman Han·Jérôme Vialard·Alexey V. Fedorov·Soong-Ki Kim
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Abstract

We use perfect-model, large-ensemble nonlinear Recharge Oscillator (RO) simulations to quantify ENSO internal variability and the detectability of forced changes in ENSO characteristics. Fixed-parameter simulations show that linear trends in ENSO standard deviation, period, and skewness as large as those observed since 1955 can arise from internal variability in 10% of simulations. RO parameters estimated from single realizations exhibit spurious drifts even without forcing, underscoring the need for ensembles. Using 100-member ensembles, comparable to the largest climate-model ensembles, we identify detectable parameter trends. For ENSO amplitude, the detectability thresholds for forced changes in underlying processes are 15% per century for stochastic forcing, 25% per century for basin adjustment, and 50% per century for the Bjerknes feedback. For ENSO period, the detectability threshold for forced changes in the underlying recharge--discharge processes and delayed oceanic feedback is 15% per century. These results provide a testbed for interpreting RO-diagnosed ENSO changes in climate-model ensembles.

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Sooman Han, Jérôme Vialard, Alexey V. Fedorov, Soong-Ki Kim. 2026-08-27. Detectability of Forced ENSO Changes under Global Warming: Insights from the Recharge Oscillator. https://arxiv.org/abs/2608.26767

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