|  |
Program |
 |
| |
 |
Special Session 6: The ocean¡¯s energy cascade and mixing |
| |
|
|
Numerical simulations of shoaling internal solitary waves of elevation
Wednesday 11th @ 1500-1520
Multi-function Hall
Chengzhu Xu* , University of Waterloo
Christopher Subich, Environment Canada
Marek Stastna, University of Waterloo
Presenter Email: c2xu@uwaterloo.ca
|
| Internal solitary waves are commonly observed in the Earth¡¯s atmosphere and oceans. Depending on the density stratification and background current, these waves may attain extremely large amplitudes, and in some cases form a recirculating, or trapped, core, transporting mass and energy as the waves propagate. While the majority of past work has examined waves of depression as they are commonly observed in oceans and deep lakes, waves of elevation, which occur when the pycnocline is below the mid-depth, are more typical of shallow waters such as near-coastal regions. We will present high-resolution, two-and three-dimensional direct numerical simulations of large amplitude internal solitary waves of elevation on the laboratory scale, shoaling onto and over a small-amplitude shelf. The three-dimensional, mapped coordinate, spectral collocation method used for the simulations allows for accurate modelling of both the shoaling waves and the bottom boundary layer. In order to understand the interaction between the wave and the bottom boundary, numerical experiments were performed with both smooth and corrugated bottom boundaries. On a smooth bottom boundary, the shoaling of the waves is characterized by the formation of a quasi-trapped core which undergoes a spatially growing stratified shear instability at its edge and a lobe-cleft instability in its nose. Both of these instabilities develop and three-dimensionalize concurrently, leading to strong bottom shear stress. With a corrugated bottom boundary, boundary layer separation is found during the waves' shoaling process. This more complex boundary layer phenomenology precludes the formation of the lobe-cleft instability almost completely and hence provides a different mechanism for fluid and material exchange across the bottom boundary layer. Our analyses suggest that all of these wave-induced instabilities can lead to enhanced turbulence in the water column and increased shear stress on the bottom boundary. Through the generation and evolution of these instabilities, the shoaling of internal solitary waves of elevation is likely to provide systematic mechanisms for material mixing, cross-boundary layer transport, and sediment resuspension. |
|
|
|
|