Numerical investigation on the generation and evolution of nonlinear internal waves in the southern Strait of Georgia

Abstract

The generation and subsequent evolution of nonlinear internal waves (NLIWs) in the Strait of Georgia (British Columbia, Canada) is investigated with both remote sensing images and a three-dimensional regional non-hydrostatic numerical simulation. Many satellite images depict clear snapshots of two successive NLIWs propagating northward about 1 h or 4 km apart during the flood tides. In the model results, local energy budget analysis demonstrates that the generation processes of internal waves are dominated by the energy conversion from barotropic tides to internal tides, while propagation processes are dominated by high-frequency NLIWs after radiating away the Boundary Pass. To further investigate the generation mechanisms of local internal waves, sensitivity studies with different tidal forcing are carried out. In the standard spring tide experiment, the rank-order NLIW packets have relatively large leading waves (∼15 m amplitude) and small trailing waves radiating from the Boundary Pass, related to a complex evolution of an internal Froude number over the sill. The internal Froude number analysis also demonstrates that only when the diurnal (D1) and semidiurnal (D2) tides act in phase can paired NLIW packets be formed. However, either single D1 or D2 tides, or D1 and D2 tides not in phase, are not able to generate NLIWs, as condition of the flow remain subcritical at all times. Moreover, a series of sensitivity experiments demonstrate that the role of non-hydrostatic mode is crucial in the high-resolution model but less important in the coarse-resolution model, via comparing wave properties and wave energetics in non-hydrostatic and hydrostatic models.