Inferred boundary mixing rates from density inversions in the St. Lawrence Estuary

Sutherland, Graig (2010) Inferred boundary mixing rates from density inversions in the St. Lawrence Estuary. Masters thesis, Memorial University of Newfoundland.

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Abstract

When interfacial internal waves shoal over a sloped bottom, a fraction of the wave energy is reflected away while the rest is utilized by such processes as transport, dissipation, and mixing. In this thesis, I investigate the dissipation and mixing parameters inferred from CTD profiles in a region of high shoaling wave activity. This is done by looking at gravitationally unstable portions in the density profiles and sorting them into gravitationally stable ones. The RMS distance the water parcel must travel is referred to as the "Thorpe" scale and this can be used to infer the turbulent dissipation rate and the eddy diffusivity. This method is applied to five days of data, 28 June 2008 to 2 July 2008, obtained off the shore of Ile-aux-Lièvres in the St. Lawrence Estuary. In this region, internal waves predominantly occur between 1 and 3 hours after the local low water during the flood tide. Therefore, the variability of the inferred turbulent and mixing parameters are investigated as a function of tidal phase to determine whether these are concurrent with the increase of shoaling internal waves. The dissipation and mixing parameters associated with a couple of the larger shoaling events are individually presented in higher detail.

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