講演情報
[U02-P12]Inferring Phase Dynamics of El Niño-Southern Oscillation under Annual Forcing
*荒井 貴光1、河村 洋史1 (1.国立研究開発法人海洋研究開発機構)
キーワード：
エルニーニョ・南方振動、同期現象、位相振動子
The El Niño–Southern Oscillation (ENSO) accounts for a significant fraction of global climate variability on interannual time scales. While the period of ENSO events varies irregularly within the range of 2–7 years, El Niño events often peak in boreal winter. One approach to predicting ENSO events is to examine their synchronization with the annual cycle. Understanding this synchronization is also important for clarifying the underlying climate dynamics. Previous studies report a statistically significant 2:1 phase relationship between ENSO and the annual cycle [1,2].
In this study, we present a preliminary analysis of the synchronization properties between ENSO and the annual cycle by inferring the phase dynamics of ENSO. Recent studies have proposed data-driven methods based on Koopman operator analysis that enable the time evolution of ENSO to be represented using a rectified phase [3]. This phase evolves approximately as a harmonic oscillator. Using the rectified phase, we infer the phase dynamics of ENSO in the form of phase oscillators forced by the annual cycle [4,5]. The resulting equations describe the synchronization between ENSO and the annual cycle, enabling us to assess the strength of the annual forcing and determine whether it gives rise to phase locking at 2:1 or other rational ratios.
[1] K. Stein, A. Timmermann, and N. Schneider, Phase Synchronization of the El Niño-Southern Oscillation with the Annual Cycle, Phys. Rev. Lett. 107, 128501 (2011).
[2] K. Stein, A. Timmermann, N. Schneider, F.-F. Jin, and M. F. Stuecker, ENSO Seasonal Synchronization Theory, Journal of Climate 27, 5285 (2014).
[3] G. Froyland, D. Giannakis, B. R. Lintner, M. Pike, and J. Slawinska, Spectral analysis of climate dynamics with operator-theoretic approaches, Nat. Commun. 12, 6570 (2021).
[4] T. Arai, Y. Kawamura, and T. Aoyagi, Setting of the Poincaré section for accurately calculating the phase of rhythmic spatiotemporal dynamics, Phys. Rev. E 111, 014205 (2025).
[5] K. Ota and T. Aoyagi, Direct extraction of phase dynamics from fluctuating rhythmic data based on a Bayesian approach, arXiv:1405.4126.
In this study, we present a preliminary analysis of the synchronization properties between ENSO and the annual cycle by inferring the phase dynamics of ENSO. Recent studies have proposed data-driven methods based on Koopman operator analysis that enable the time evolution of ENSO to be represented using a rectified phase [3]. This phase evolves approximately as a harmonic oscillator. Using the rectified phase, we infer the phase dynamics of ENSO in the form of phase oscillators forced by the annual cycle [4,5]. The resulting equations describe the synchronization between ENSO and the annual cycle, enabling us to assess the strength of the annual forcing and determine whether it gives rise to phase locking at 2:1 or other rational ratios.
[1] K. Stein, A. Timmermann, and N. Schneider, Phase Synchronization of the El Niño-Southern Oscillation with the Annual Cycle, Phys. Rev. Lett. 107, 128501 (2011).
[2] K. Stein, A. Timmermann, N. Schneider, F.-F. Jin, and M. F. Stuecker, ENSO Seasonal Synchronization Theory, Journal of Climate 27, 5285 (2014).
[3] G. Froyland, D. Giannakis, B. R. Lintner, M. Pike, and J. Slawinska, Spectral analysis of climate dynamics with operator-theoretic approaches, Nat. Commun. 12, 6570 (2021).
[4] T. Arai, Y. Kawamura, and T. Aoyagi, Setting of the Poincaré section for accurately calculating the phase of rhythmic spatiotemporal dynamics, Phys. Rev. E 111, 014205 (2025).
[5] K. Ota and T. Aoyagi, Direct extraction of phase dynamics from fluctuating rhythmic data based on a Bayesian approach, arXiv:1405.4126.