Observations of Shock and Undular Bore Formation in Internal at a Shelf Break
Large amplitude internal waves at semi-diurnal tidal frequency (internal tides) are observed to be generated over the slope region of the Australian North West Shelf and propagate shoreward over shoaling bathymetry. In deep water the waves are nearly linear in shape and are seen to steepen and become strongly non-linear as they propagate. The waves steepen at the leading edge to the point where an internal hydraulic jump or shock forms. The shocks are generally downwards and are weak shocks seen as undular bores. At times a second, and weaker, backward shock forms on the trailing edge of the wave. The undular bores are followed by a train of oscillations that can be reasonably described as solitons. An analytical model using a perturbed extended Korteweg-de Vries equation is used to describe the evolution of an initially sinusoidal wave as it progagates over an exponential depth profile, in the presence of a background current of constant shear, and breaks to form a shock. The model predictions, of the distance the wave propagates before forming a shock, and of the height of the shock as it propagates, compare well with observations.
KeywordsInternal Wave Internal Tide Shelf Break Shock Strength Buoyancy Frequency
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