It has recently been proposed that the broad spectrum of interannual v
ariability in the tropics with a peak around four years results from a
n interaction between the linear low-frequency oscillatory mode of the
coupled system and the nonlinear higher-frequency modes of the system
. In this study we determine the bispectrum of the conceptual model co
nsisting of a nonlinear low-order model coupled to a linear oscillator
for various values of the coupling constants.