Bolus degeneration on uniform slopes

Abstract

Shoaling internal solitary waves (ISWs) occur on nearly every coastline worldwide but are difficult to track between moorings as they shoal, fission into boluses and ultimately degenerate. In the present study, experiments in a 18 m long internal wave flume, measured the rate of dissipation of turbulent kinetic energy, as boluses shoaled, in order to parameterize the associated dissipation lengthscale. Dissipation was proportional to incident wave amplitude and wave Reynolds number, from 102 (lab) to 106 (coastal ocean). However, energetics calculations (wave energy/dissipation rate) failed to predict the dissipation lengthscale, which was empirically parameterized as a function of the wave Reynolds number (R2 = 0.84 to 0.96), the wave Froude number (R2 = 0.83) and the internal Iribarren number (R2 = 0.94). These parameterizations may be readily applied to oceanic mooring data, as they only require knowledge of the bulk incident wave properties and the bottom boundary slope. We found that shoaling ISWs propagate significantly further than boluses (∼10 times further in the lab and ∼100 times further in coastal ocean) and, therefore, it is important to distinguish these waveforms when computing dissipation lengthscales from observations.