A study of self-excited oscillations of the tropical ocean- atmosphere system. Part II: nonlinear cases

Abstract

The coupling from ocean to atmosphere is idealized as a nonlinear relation τ(he) between a wind stress τ of fixed spatial form and he, the thermocline displacement at the eastern end of the equator. A period doubling bifurcation leads from a period of less than two years to 3-4 year one observed in nature. Other principal results are: the resulting period depends on the curvature of the function away from the unstable equilibrium at he = 0, and not solely on its linear instability; at least two Rossby modes must be included in the model for aperiodic oscillations to appear; no stochastic term is needed for this aperiodicity, but it appears more readily if the model background state includes an annual cycle. -from Authors