Numerical experiments of internal wave generation by strong tidal flow across a finite amplitude bank edge

TLDR

The study is motivated by the need to understand complex internal wave phenomena observed on Georges Bank and other strong tidal forcing sites. The authors use a two‑dimensional, fully nonlinear, nonhydrostatic Boussinesq model on an f‑plane with observation‑based forcings and uniform stratification, exploring sensitivity to slope, current strength, stratification, and initialization. The model reproduces a large depression, a hydraulic jump over the bank edge, two on‑bank propagating depressions per tidal cycle, and an undular bore, with rotational effects driving the second on‑bank depression.

Abstract

Results of some idealized numerical experiments of strong tidal flow of a stratified fluid across a finite amplitude bank edge are presented. These experiments were motivated by a need to develop an understanding of some of the complex internal wave phenomena observed on Georges Bank (Loder et al., 1992) and at other locations where tidal forcing is strong. The numerical model solves the fully nonlinear, nonhydrostatic Boussinesq equations on an ƒ plane. The model is two‐dimensional, with spatial variation in the vertical and cross‐bank directions only. Model forcings are based on the Georges Bank observations. A horizontally uniform stratification is used. The model successfully reproduces some observed features including the formation of a large depression and a hydraulic jump over the bank edge during off‐bank flow and two on‐bank propagating depressions every tidal period. An undular bore propagating away from the bank is in agreement with other observations (La Violette et al., 1990). Rotational effects are shown to be responsible for the formation of the second of the on‐bank propagating depressions. Sensitivity of the results to the topographic slope, tidal current strength, stratification, and model initialization is explored.