Tidal energy conversion in a global hot spot: On the 3‐D dynamics of baroclinic tides at the Celtic Sea shelf break

Abstract

Globally, the Celtic Sea shelf break is ranked highest as an energetic ''hot spot'' of tidal energy conversion, therefore making it the most significant contributor to global internal tidal energy flux. In this paper, the three-dimensional dynamics of baroclinic tides in the shelf-slope area of the Celtic Sea was investigated numerically and using observational data collected on the 376th cruise of the RV ''RRS Discovery'' in June 2012. The time series recorded at a shelf break mooring showed that semidiurnal internal waves were accompanied by packets of internal solitary waves with maximum amplitudes up to 105 m, the largest internal waves ever recorded in the Celtic Sea, and ranking among the largest observed in the global ocean. The observed baroclinic wavefields were replicated numerically using the Massachusetts Institute of Technology general circulation model. A fine-resolution grid with 115 m horizontal and 10 m vertical steps allowed the identification of two classes of short-scale internal waves. The first classification was generated over headlands and resembles spiral-type internal waves that are typical for isolated underwater banks. The second classification, generated within an area of several canyons, revealed properties of quasi-planar internal wave packets. The observed in situ intensification of tidal bottom currents at the shelf break mooring is explained in terms of a tidal beam that was formed over supercritical bottom topography at the mooring location.

The Whittard Canyon – A case study of submarine canyon processes

“…The semi-diurnal tide has been observed to drive 28-48W m -1 of energy on-shelf , with the positive on-shelf energy flux modulated by nonlinear interaction between the vertical velocity associated with the semi-diurnal internal tide, and the vertical shear of inertial oscillations, leading to an increase of 25-43% in the energy flux. Internal solitary waves with amplitudes reaching a maximum of 105 m have also been reported (Vlasenko et al, 2014). The internal tide generated at the shelf break has been observed as a coherent signal up to 170 km onto the Celtic Sea shelf (Inall et al, 2011).…”

Nonlinear interfacial wave formation in three dimensions

“…The calculations are motivated by recent field observations ) and numerical ocean modelling calculations (Vlasenko et al 2013(Vlasenko et al , 2014. Using the linear long-wave speed c 0 as the velocity scale, the tidal ellipse observed in the field becomes in non-dimensional terms (u 1 , u 2 )/c 0 = (0.5, 0.8).…”

“…Palmer et al (2013). A wave amplitude up to 105 m in shallow parts of the Celtic Sea has been measured (Vlasenko et al 2014).…”

Long ring waves in a stratified fluid over a shear flow

“…Tidal generation of internal waves in the Celtic Sea has been modelled by Vlasenko et al (2013Vlasenko et al ( , 2014 and Grue (2015). We note that the waves generated in the Strait of Gibraltar are nearly annular (see figure 1), as are the waves generated near a sea mountain in the Celtic Sea (see Vlasenko et al (2014, figure A1)). …”