Dissipative Losses in Nonlinear Internal Waves Propagating across the Continental Shelf

Abstract

A single nonlinear internal wave tracked more than 100 wavelengths across Oregon?s continental shelf over a 12-h period exhibited nearly constant wave speed, c = 0.75 m s?1, and amplitude, a = 15 m. The wavelength L gradually decreased from 220 m in 170-m water depth to 60 m in 70-m water depth. As the water shallowed beyond 50 m, the wave became unrecognizable as such. The total energy decreased from 1.1 to 0.5 MJ m?1. The rate at which wave energy was lost, ?dE/dt = 14 [7, 22] W m?1, was approximately equal to the energy lost to turbulence dissipation, ?ε = 10 [7, 14] W m?1, as inferred from turbulence measurements in the wave cores plus estimates in the wave-induced bottom boundary layer. The approximate balance, dE/dt = ??ε, differs from the solibore model of Henyey and Hoering in which the potential energy across the wave balances ?ε. However, other evidence suggests that the wave evolved from a solibore-like state to a dissipative solitary wavelike state over the observed propagation path.