Han S. auteur aut IRD Pedorov L. auteur aut IRD Vialard Jérôme auteur aut IRD text journalArticle eng The dynamics of El Ni & ntilde;o-Southern Oscillation (ENSO) are succinctly captured by the recharge oscillator (RO) framework. However, to simulate ENSO realistically, careful choices must be made regarding the RO's key parameters. In particular, nonlinear parameters govern how well the model reproduces ENSO asymmetries El Ni & ntilde;o events tend to be stronger but relatively short, often transitioning into La Ni & ntilde;a, whereas La Ni & ntilde;a events are typically weaker but may last longer. While amplitude asymmetry has been studied within the RO framework, duration and transition asymmetries remain less explored and their causes are debated. In this study, by systematically exploring the RO parameter spacerather than relying on commonly used fitting methods we identify optimal parameter values that successfully capture key linear and nonlinear ENSO characteristics. In doing so, we revisit several foundational elements of the RO framework. First, we analytically derive the phase relationship between temperature and heat content anomalies, showing that it depends on the signs of the Bjerknes feedback and the ocean damping time scale. We show that self-sustained oscillations fail to reproduce the observed kurtosis of Ni & ntilde;o indices. We further derive an analytical expression for the power spectrum and argue that incorporating red noise forcing, rather than white noise, introduces unnecessary complexity. The most realistic yet simplest RO configuration is a strongly damped oscillator, with a decay time scale shorter than the dominant period, forced by multiplicative white noise and influenced by weak deterministic nonlinearities. Identifying these minimal components preserves the RO framework's clarity and isolates the core physical processes underlying ENSO behavior. specialized ENSO Numerical analysis/modeling Idealized models Stochastic models 032 020 39 1 77-101 2026 0894-8755 https://www.documentation.ird.fr/hor/PAR00030643 10.1175/jcli-d-25-0250.1 0894-8755 https://www.documentation.ird.fr/hor/PAR00030643 IRD - Base Horizon / Pleins textes 2026-02-04 2026-02-04 PAR00030643 fre