HR: 10:40h
AN: NG32A-02    [Abstracts]
TI: A delay differential model of ENSO variability: parametric instability and the distribution of extremes
AU: * Zaliapin, I
EM: zal@unr.edu
AF: Department of Mathematics and Statistics, University of Nevada, Reno, NV 89557, United States
AU: Ghil, M
EM: ghil@atmos.ucla.edu
AF: Department of Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
AU: Thompson, S
EM: thompson@radford.edu
AF: Department of Mathematics and Statistics, Radford University, Radford, VA 24142, United States
AB: We consider a Delay Differential Equation (DDE) model for El-Nino Southern Oscillation (ENSO) variability. The model combines two key mechanisms that participate in the ENSO dynamics: delayed negative feedback and seasonal forcing. Descriptive and metric stability analyses of the model are performed in a complete 3D space of its physically relevant parameters. Existence of two regimes --- stable and unstable --- is reported. The domains of the regimes are separated by a sharp neutral curve in the parameter space. The detailed structure of the neutral curve become very complicated (possibly fractal), and individual trajectories within the unstable region become highly complex (possibly chaotic) as the atmosphere-ocean coupling increases. In the unstable regime, spontaneous transitions in the mean "temperature" (i.e., thermocline depth), period, and extreme annual values occur, for purely periodic, seasonal forcing. This indicates (via the continuous dependence theorem) the existence of numerous unstable solutions responsible for the complex dynamics of the system. In the stable regime, only periodic solutions are found. Our results illustrate the role of the distinct parameters of ENSO variability, such as strength of seasonal forcing vs. atmosphere ocean coupling and propagation period of oceanic waves across the Tropical Pacific. The model reproduces, among other phenomena, the Devil's bleachers (caused by period locking) documented in other ENSO models, such as nonlinear PDEs and GCMs, as well as in certain observations. We expect such behavior in much more detailed and realistic models, where it is harder to describe its causes as completely.
DE: 3215 Instability analysis
DE: 4410 Bifurcations and attractors
DE: 4445 Nonlinear differential equations
DE: 4522 ENSO (4922)
DE: 4922 El Nino (4522)
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting