Dissipation in Internal Tides and Solitary Waves

Abstract

Solitons have been observed and studied on the Scotian Shelf using the vertical microstructure profiler EPSONDE. During one tidal cycle a packet of solitary waves has been sampled four times as it propagated onto the shelf to examine its evolution and decay. Enhanced turbulence and mixing were observed to occur in the strongest shear region of the wave packet as expected. About 20% of the energy lost as the solitary wave packet decayed can be attributed to turbulent dissipation. The effects of nonlinearity, dissipation, and dispersion are explored in terms of the Korteweg-de Vries-Burgers (KdVB) equation. The dispersive timescale is always much shorter than the dissipative timescale, and both decrease as the soliton moves onshelf. The mean dissipation timescale, of 12 h compared to the dispersion timescale of less than 1 h, suggests that the waves are consistent with the KdVB description. Calculated vertical diffusivities are in the range of 10(-5)-10(-4) m(2) s(-1).