Spectral-element-based simulation of a model internal swash zone

Internal swash zones (ISZs) (Emery and Gunnerson 1973 ) are regions which develop along sloping oceanic boundaries through the action of periodically incident internal waves (IWs) in a manner analogous to a surface swash zone on the beach, albeit at slower timescales (O(10 minutes) or longer) and over longer wavelengths (O(10 km) or longer). Moreover, such waves drive mixing of near-boundary fluid and energize the bottom boundary layer. We examine the design and implementation of a numerically simulated ISZ in a two-layer continuous stratification. The setup and computational investigations are motivated by an on-going field project which focuses on the ISZ energized by the internal seiche in seasonally stratified Cayuga lake in NY state (Schweitzer 2015). The lake ISZs are an efficient proxy for equivalent physical processes driven by the lower-mode internal tide on the oceanic continental slope.

We will first present a two-dimensional study of the interaction of finite-amplitude incident periodic waves with a linearly sloping boundary over 3 wave periods for different values of wavelengths, Froude numbers and stratification choices. We will highlight the importance of the choice of the sea-bed boundary condition (no-slip/free-slip) in the breaking mechanisms. We will also present the preliminary results of three-dimensional simulations of internal-wave-induced transition to turbulence on the sloping boundary.