El Nino Southern Oscillation Nonlinear modeling, satellite data, and Fourier analysis

摘要

Interaction between the tropical ocean and atmosphere produces interannual climate variability dominated by the El Nino Southern Oscillation (ENSO). We perform a Fourier analysis of the El Nino events, which are characterized by positive sea-surface temperature (SST) anomalies. We consider an elementary nonlinear model for the ENSO phenomenon: the time rate of change of the SST depends on the existence of a strong positive feedback in the coupled ocean-atmosphere system, and on a nonlinear mechanism that limits the growth of unstable perturbations. A key element in this model is the inclusion of the effects of equatorially trapped oceanic waves propagating in a closed basin through a time delayed term. Numerical solution reveals solutions that are self-sustained oscillations. The model is extended by including external influences such as annual forcing, global warming, and stochastic effects. We investigate the range of the parameters that will cause drastic qualitative changes in the climate system, i.e. bifurcation.