More Like this

1. The impact of outer‐bar alongshore variability on inner‐bar rip dynamics

   https://doi.org/10.1002/esp.70086  

   Fritzbøger_Christensen, Drude; Raubenheimer, Britt; Elgar, Steve (May 2025, Earth Surface Processes and Landforms)

   Abstract A field‐calibrated morphodynamic model (MIKE21) is used to investigate the importance of the dimensions of a rip channel across an outer sand bar to the hydrodynamics and morphological evolution of an inner sand bar and rip channel for a range of initial bathymetries and wave conditions. The model was driven with offshore wave conditions and idealized bathymetry representative of field conditions near Duck, NC, USA during which strong rips and associated channel erosion were observed to occur over an inner bar. Consistent with prior results, the strength of the hydro‐morphological coupling between the two bars depends on the dimensions of the outer‐bar perturbation, as well as the wave forcing. The results suggest that in double‐barred systems, a single moderate‐scale perturbation (O(0.1 m deep, 10 m wide)) in the outer‐bar elevation can lead to the generation of a rip current and associated erosion of a rip channel across the inner bar. The simulations suggest that the magnitude of the inner‐bar rip flow, the depth to which the inner‐bar channel is eroded, and the alongshore position of the inner‐bar rip relative to the outer‐bar perturbation depend on the non‐dimensional outer‐bar channel depth, the transverse rip‐channel slope, and the wave height, period and directional spreading. For deep and narrow outer‐bar channels, the outer‐inner bar coupling is strong. In contrast, for shallow and wide outer‐bar channels, the system may alternate between being coupled and uncoupled with unstable locations of the inner‐bar rip. 

   more » « less
2. Rip current likelihood as a function of incident wave conditions for different bathymetries

   https://doi.org/10.1016/j.apor.2025.104727  

   Choi, Junwoo; Elgar, Steve; Kirby, James T (September 2025, Applied Ocean Research)

   The likelihood of rip currents as a function of water depth (tidal level), incident wave height, period, direction, and spectral spreading in both frequency and direction is investigated with a Boussinesq numerical model (FUNWAVE) for alongshore uniform, moderately variable, and strongly variable bathymetry, providing two- dimensional probability distributions of rip-current occurrence along the coast. The simulations suggest that over strongly irregular alongshore bathymetry rip-current likelihood increases with longer wave periods and narrower directional spectra. In contrast, over more uniform alongshore bathymetry, rip current likelihood in- creases with shorter wave periods and broader directional spectra. The simulations suggest that as bathymetric variability increases, the effects of different incident wave fields decreases. 

   more » « less
3. A Regime Diagram for Internal Lee Waves in Coastal Plain Estuaries

   https://doi.org/10.1175/JPO-D-21-0261.1  

   Li, Renjian; Li, Ming (December 2022, Journal of Physical Oceanography)

   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. 

   more » « less
4. Reabsorption of Lee-Wave Energy in Bottom-Intensified Currents

   https://doi.org/10.1175/JPO-D-22-0058.1  

   Wu, Yue; Kunze, Eric; Tandon, Amit; Mahadevan, Amala (October 2022, Journal of Physical Oceanography)

   Abstract While lee-wave generation has been argued to be a major sink for the 1-TW wind-work on the ocean’s circulation, microstructure measurements in the Antarctic Circumpolar Currents find dissipation rates as much as an order of magnitude weaker than linear lee-wave generation predictions in bottom-intensified currents. Wave action conservation suggests that a substantial fraction of lee-wave energy can be reabsorbed into bottom-intensified flows. Numerical simulations are conducted here to investigate generation, reabsorption and dissipation of internal lee waves in a bottom-intensified, laterally confined jet that resembles a localized abyssal current over bottom topography. For the case of monochromatic topography with | kU 0 | ≈ 0.9 N , where k is the along-stream topographic wavenumber, | U 0 | near-bottom flow speed and N buoyancy frequency, Reynolds-decomposed energy conservation is consistent with linear wave action conservation predictions that only 14% of lee-wave generation is dissipated, with the bulk of lee-wave energy-flux reabsorbed by the bottom-intensified flow. Thus, water column reabsorption needs to be taken into account as a possible mechanism for reducing the lee-wave dissipative sink for balanced circulation. 

   more » « less
5. Generation of Internal Lee Waves by Lateral Circulation in a Coastal Plain Estuary

   https://doi.org/10.1175/JPO-D-18-0142.1  

   Xie, Xiaohui; Li, Ming (July 2019, Journal of Physical Oceanography)

   Recent mooring observations at a cross-channel section in Chesapeake Bay showed that internal solitary waves regularly appeared during certain phases of a tidal cycle and propagated from the deep channel to the shallow shoal. It was hypothesized that these waves resulted from the nonlinear steepening of internal lee waves generated by lateral currents over channel-shoal topography. In this study numerical modeling is conducted to investigate the interaction between lateral circulation and cross-channel topography and discern the generation mechanism of the internal lee waves. During ebb tides, lateral bottom Ekman forcing drives a counterclockwise (looking into estuary) lateral circulation, with strong currents advecting stratified water over the western flank of the deep channel and producing large isopycnal displacements. When the lateral flow becomes supercritical with respect to mode-2 internal waves, a mode-2 internal lee wave is generated on the flank of the deep channel and subsequently propagates onto the western shoal. When the bottom lateral flow becomes near-critical or supercritical with respect to mode-1 internal waves, the lee wave evolves into an internal hydraulic jump. On the shallow shoal, the lee waves or jumps evolve into internal bores of elevation. 

   more » « less