Dissipative Losses in Nonlinear Internal Waves Propagating across the Continental Shelf

Abstract

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, ρɛ = 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 = −ρɛ, differs from the solibore model of Henyey and Hoering in which the potential energy across the wave balances ρɛ. However, other evidence suggests that the wave evolved from a solibore-like state to a dissipative solitary wavelike state over the observed propagation path.