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Abstract Using an idealized channel representative of a coastal plain estuary, we conducted numerical simulations to investigate the generation of internal lee waves by lateral circulation. It is shown that the lee waves can be generated across all salinity regimes in an estuary. Since the lateral currents are usually subcritical with respect to the lowest mode, mode-2 lee waves are most prevalent but a hydraulic jump may develop during the transition to subcritical flows in the deep channel, producing high energy dissipation and strong mixing. Unlike flows over a sill, stratified water in the deep channel may become stagnant such that a mode-1 depression wave can form higher up in the water column. With the lee wave Froude number above 1 and the intrinsic wave frequency between the inertial and buoyancy frequency, the lee waves generated in coastal plain estuaries are nonlinear waves with the wave amplitude Δ h scaling approximately with , where V is the maximum lateral flow velocity and is the buoyancy frequency. The model results are summarized using the estuarine classification diagram based on the freshwater Froude number Fr f and the mixing parameter M . The Δ h decreases with increasing Fr f as stronger stratification suppresses waves, and no internal waves are generated at large Fr f . The Δ h initially increases with increasing M as the lateral flows become stronger with stronger tidal currents, but decreases or saturates to a certain amplitude as M further increases. This modeling study suggests that lee waves can be generated over a wide range of estuarine conditions.
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Secondary generation of breaking internal waves in confined basins by gravity currents
In confined stratified basins, wind forcing is an important mechanism responsible for the onset and generation of internal waves and seiches. Previous observations have also found that gravity currents in stratified environments can also initiate internal waves. We conducted a series of laboratory experiments to investigate the generation of internal motions due to such dense gravity currents on an incline entering a two-layer stratification, focusing in particular on the interaction between the onset of internal motions and topography and diapycnal mixing due to breaking internal waves. The baroclinic response of the ambient stratification to the gravity current is found to be analogous to a system forced by a surface wind stress, and the response as characterized by a Wedderburn-like number was found to be linearly proportional to the initial gravity current Richardson number. The generated internal motions are characterized as having a low-frequency internal surge and higher-frequency progressive internal waves. The overall mixing efficiency of the breaking internal wave was calculated and found to be low compared with similar previous studies.
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- Award ID(s):
- 2022930
- PAR ID:
- 10273227
- Date Published:
- Journal Name:
- Journal of Fluid Mechanics
- Volume:
- 917
- ISSN:
- 0022-1120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/jfm.2021.309
