Diagnosing the Linear Periodicity Dynamics of ENSO for Its Two Spatiotemporal Modes

Abstract

AbstractThe El Niño–Southern Oscillation (ENSO) is mainly manifested as the quasi‐biennial (QB) and low‐frequency (LF) coupled modes centered at different longitudes. Based on the recharge oscillator framework, we propose a new method to diagnose the linear periodicity dynamics of spatiotemporally diverse ENSOs, for example, the two coupled modes, to which the traditional Wyrtki index method is ineligible. This method is applied to reanalysis data sets and models and validated by comparisons with the Wyrtki index, which shows that the periodicity of the LF mode is dominated by the thermocline feedback (TH) and effectively reproduced by models, whereas the periodicity of the QB mode is equally driven by the TH and zonal advective feedback (ZA) and poorly simulated in most models due to the insufficient ZA simulations. The new method provides an effective tool for a deeper understanding of the multi‐timescale nature of diverse ENSOs and improving their representations in future models.