Energy transfer between surface and internal waves in the North Pacific Ocean

Abstract

The energy transfer between internal and surface waves is formulated as a scattering process of surface waves by packets of internal waves. For weak internal wave fields, the Born approximation may be used, and this is shown to give the same transfer rate as the “modulation model” of the resonant triad theory for weak nonlinear interactions. For stronger internal wave fields, the eikonal theory of ray paths is used to calculate surface wave scattering. The theory is applied to historical Väisälä frequency profiles and wind data for the North Pacific ocean. Energy transfer rates from the internal wave to the surface wave field in the range of 10−4 W/m2 and higher are found, except during winter months at higher latitudes, where the rates are somewhat lower. For the weaker internal wave fields, the resonant triad theory (or, equivalently, the Born theory) must be used. For the strongest fields observed, the weak interaction theory is not valid and the interaction is described as ray path scattering. There is a region of overlap for which the two theoretical models give comparable results.