Decadal Oceanic Response to Stochastic Wind Forcing

Abstract

The low-frequency linear eigenmodes of the reduced-gravity shallow-water equations with weak friction are calculated numerically and using an analytic approximation. For basins with a large variation of the Coriolis parameter, large-scale eigenmodes emerge: the eigenfrequencies are integer multiples of the frequency for the gravest mode, which, in turn, has a period given by the transit time of the slowest long Rossby wave. The efolding decay times are comparable to the period and independent of friction. These eigenmodes are excited by stochastic wind forcing and this leads to a weak peak in the spectral response near the frequency of the leastdamped eigenmode. This decadal-frequency peak is most evident on the eastern and western boundaries and in the equatorial region of the basin.