A Boolean delay equation model of ENSO variability (original) (raw)
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Understanding ENSO variability and its extrema: A delay differential equation approach
2009
Abstract We review and analyze in further detail a simple model of El-Nino/Southern-Oscillation (ENSO) variability. The model is formulated as a forced delay differential equation for sea surface temperature T in the Tropical Pacific, and it combines two key mechanisms that participate in ENSO dynamics: delayed negative feedback and seasonal forcing.
2010
We consider a highly idealized model for El Nino/Southern Oscillation (ENSO) variability, as introduced in an earlier paper. The model is governed by a delay differential equation for sea surface temperature in the Tropical Pacific, and it combines two key mechanisms that participate in ENSO dynamics: delayed negative feedback and seasonal forcing. We perform a theoretical and numerical study of the model in the three-dimensional space of its physically relevant parameters: propagation period of oceanic waves across the Tropical Pacific, atmosphere-ocean coupling, and strength of seasonal forcing. Phase locking of model solutions to the periodic forcing is prevalent: the local maxima and minima of the solutions tend to occur at the same position within the seasonal cycle. Such phase locking is a key feature of the observed El Nino (warm) and La Nina (cold) events. The phasing of the extrema within the seasonal cycle depends sensitively on model parameters when forcing is weak. We al...
Reassessing Conceptual Models of ENSO
Journal of Climate, 2015
The complex nature of the El Niño–Southern Oscillation (ENSO) is often simplified through the use of conceptual models, each of which offers a different perspective on the ocean–atmosphere feedbacks underpinning the ENSO cycle. One theory, the unified oscillator, combines a variety of conceptual frameworks in the form of a coupled system of delay differential equations. The system produces a self-sustained oscillation on interannual time scales. While the unified oscillator is assumed to provide a more complete conceptual framework of ENSO behaviors than the models it incorporates, its formulation and performance have not been systematically assessed. This paper investigates the accuracy of the unified oscillator through its ability to replicate the ENSO cycle modeled by flux-forced output from the Australian Community Climate and Earth-System Simulator Ocean Model (ACCESS-OM). The anomalous sea surface temperature equation reproduces the main features of the corresponding tendency ...
Atmosphere–Ocean Interactions at Strong Couplings in a Simple Model of El Niño
Journal of Climate, 2013
The understanding of the dynamics of the El Niño–La Niña phenomenon in the tropical Pacific has been the subject of an impressive number of works in the last 20 years. The delayed oscillator theory provides an interpretative framework that has allowed enormous advances in understanding. Much evidence that stochastic forcing does play a role in the dynamics of ENSO has been discussed and it is possible to shape a theory of El Niño as a stochastically forced linear system. However, it is still uncertain if El Niño is a self-sustained nonlinear oscillatory system, a chaotic system, or a stochastically forced linear system. The authors propose in this paper that it is possible to have realistic El Niño probability distributions assuming that the system is a nonlinear stochastically forced system. In this paper a simple system is proposed that retains the main characteristics of the El Niño–La Niña variations, such as the skewness and the autocorrelation, and it is shown how solutions fo...