q 2000 American Meteorological Society Decadal Variability in a Simplified Wind-Driven Ocean Model

The impact of an unsteady wind forcing on oceanic low-frequency variability is conceptually studied using a reduced-gravity shallow-water model. A time-averaged wind forcing and a simple ocean–atmosphere coupling is completed by a stochastic component (spatially coherent white noise) representing the effect of atmospheric transient eddies. To account for the observed concentration of eddy activity along the North Atlantic and North Pacific storm tracks the variance of the stochastic forcing is chosen to be spatially inhomogeneous. Low-frequency variability of the basin-averaged energetics shows a dominant spectral peak with an amplitude depending on the inhomogeneity of the stochastic forcing and the time-averaged wind stress. The period of the variability is unexpected considering baroclinic Rossby waves forced by the ocean–atmosphere coupling only. This variability can be explained by ‘‘spatial resonance’ ’ of the forced baroclinic Rossby wave and the Reynolds momentum flux induced by the spatially inhomogeneous white noise. 1