Generation of internal solitary waves over a large sill: From Knight Inlet to Luzon Strait

Abstract

A fully nonlinear, nonhydrostatic numerical model is utilized to investigate the generation of Internal Solitary Waves (ISWs) upstream of the Knight Inlet sill. While an upstream hydraulic jump initiates the ISW generation and both hydraulic jump and upstream influence contribute to the generation, it is found that upstream influence is dominant and the hydraulic jump is not necessary for the ultimate generation of ISWs. Decreasing the tidal forcing or upstream sill width may render the flow subcritical (i.e., the hydraulic jump disappears) and ISWs can be generated by nonlinear steepening of long wave disturbances induced by upstream influence. Increasing the tidal forcing or upstream sill width may generate a hydraulic jump blocking strong upstream propagating disturbances. The jump subsequently becomes a turbulent bore and later disperses into a train of ISWs as the tide relaxes. Further increase in the tidal forcing may sweep the turbulent bore downstream and a train of ISWs is emitted upstream toward the end of waning tide. By reducing the stratification strength by 1 order of magnitude, the near‐sill flow is in the transcritical regime and ISWs are resonantly generated over the lee side slope. Connections to the internal tide release mechanism at Luzon Strait and to the unsteady lee wave model are also discussed. The present work provides some more insights into the ISW generation process at Knight Inlet and the connection between the generation mechanism at Knight Inlet and that at Luzon Strait is identified.

A nonhydrostatic oceanic regional model, ORCTM v1, for internal solitary wave simulation

“…Furthermore, the maximum topographic Froude number is just 0.3362 around the east ridge with the approach to the regime transition value 1/3, which ensures that the nonlinear hydraulic jump can grow with lee waves on the east of the east ridge. All of the above can explain the generation of the internal tide beam and hydraulic jump well in our simulation and confirm the mixed tidal lee wave regime in the Luzon Strait (Chen et al, 2017).…”

“…A significant hydraulic jump can appear with the isotherm fluctuation up to roughly 200 m on the eastern side, which indicates the formation of lee waves to a certain extent. The above internal wave generation due to tide-topography interactions can be described with the below nondimensional parameters at the source: (1) the tidal excursion parameter ε = U 0 /Lω, which can be associated with the generation of an internal tide beam under critical or supercritical topography, where U 0 is barotropic current amplitude from the far field and L is the characteristic length for topography (Garret and Kunze, 2007;Chen et al, 2017); (2) the Froude number F r = U/c and its topographic form F r z = ω/N (dH /dx), in which c is the mode-1 linear speed for the eigenvalue problem (Legg and Adcroft, 2003; see Appendix B). Specifically, Legg and Klymak (2008) found that the nonlinear hydraulic jump will develop with lee wave generation when F r z < 1/3.…”

The Influence of ENSO on the Structure of Internal Tides in the Xisha Area

“…We classified the warm and cold episodes of the ENSO events following the method described by Chu et al (2017) 2014). Numerical experiments and observations have both revealed that the structure of stratification affects the generation of ITs (Chen et al, 2017;Guo et al, 2012;Jeon et al, 2014). To explore the impact of stratification on the vertical structure of ITs, we plotted year-averaged HKE of different modes in El Niño and La Niña years (Figures 7b-7e).…”

Internal Waves Along the Malvinas Current: Evidence of Transcritical Generation in Satellite Imagery

“…In the framework of resonant generation, this characteristic length is considered here as a proxy for the interfacial disturbances originating near forcing bathymetry as a result of the stratified flow. Note that the characteristic length of these interfacial disturbances usually compares with the already developed packets rather than with their individual waves (e.g., see Farmer andArmi, 1999, andChen et al, 2017). Nonetheless, changing this length scale results in changes at most of about 0.1 m s -1 in c in Equation 1 (when considering a depth of 500 m, where most of the observations were made).…”