Internal hydraulic jumps and solitons at a shelf break region on the Australian North West Shelf

Abstract

A large‐amplitude, shoreward propagating, semidiurnal internal tide has previously been observed at a shelf break region on the Australian North West Shelf. This paper discusses detailed observations of the wave shape as the internal tide shoals over the shelf slope, near the shelf break. The leading face of the internal tide is seen to steepen and form an internal hydraulic jump. The properties of the jump are well described by a two‐layer hydraulic jump model in which the nearly uniform background temperature (density) profile is strongly distorted by the internal tide to an approximately two‐layer stratification just before a jump. The height of the jumps reaches 60 m in 123 m water depth, and the jumps contribute significantly to the strong dissipation of the internal tide that has previously been observed in this region. Following some of the jumps, packets of ∼ 12 internal waves of 20 min period are observed. These are described as solitons, and it is found that a second‐order theory (in wave amplitude) is necessary to describe the wavelength and phase speed. These waves also play an important role in the energy dissipation of the internal tide.