Coupling of the El Niño–Southern Oscillation (ENSO) and Indian monsoon (IM) is central to seasonal summer monsoon rainfall predictions over the Indian subcontinent, although a nonstationary relationship between the two nonlinear phenomena can limit seasonal predictability. Radiative effects of volcanic aerosols injected into the stratosphere during large volcanic eruptions (LVEs) tend to alter ENSO evolution; however, their impact on ENSO-IM coupling remains unclear. Here, we investigate how LVEs influence the nonlinear behavior of the ENSO and IM dynamical systems using historical data, 25 paleoclimate reconstructions, last-millennium climate simulations, large-ensemble targeted climate sensitivity experiments, and advanced analysis techniques. Our findings show that LVEs promote a significantly enhanced phase-synchronization of the ENSO and IM oscillations, due to an increase in the angular frequency of ENSO. The results also shed innovative insights into the physical mechanism underlying the LVE-induced enhancement of ENSO-IM coupling and strengthen the prospects for improved seasonal monsoon predictions.

厄尔尼诺—南方涛动（ENSO）和印度季风（IM）的耦合是印度次大陆夏季季风季风预报的核心，尽管这两个非线性现象之间的非平稳关系可能会限制季节性可预报性。大型火山爆发（LVE）期间注入平流层的火山气溶胶的辐射效应往往会改变ENSO的演化；然而，它们对ENSO-IM耦合的影响尚不清楚。在这里，我们使用历史数据，25次古气候重建，近千年气候模拟，大集合目标气候敏感性实验和先进的分析技术，研究LVE如何影响ENSO和IM动态系统的非线性行为。我们的发现表明，由于ENSO角频率的增加，LVE可以大大增强ENSO和IM振荡的相位同步。结果也为LVE引起的ENSO-IM耦合增强的物理机制提供了新颖的见解，并为改进季风季风预报奠定了基础。