Surface Wave Effects on High-Frequency Currents over a Shelf Edge Bank

2013 ◽  
Vol 43 (8) ◽  
pp. 1627-1647 ◽  
Author(s):  
H. W. Wijesekera ◽  
D. W. Wang ◽  
W. J. Teague ◽  
E. Jarosz ◽  
W. E. Rogers ◽  
...  
Keyword(s):  
Surface Wave ◽  
Kinetic Energy ◽  
Mixed Layer ◽  
High Frequency ◽  
Pressure Sensors ◽  
Stokes Drift ◽  
Langmuir Circulation ◽  
Temperature Conductivity ◽  
Wave Focusing ◽  
Wave Effects

Abstract Several acoustic Doppler current profilers and vertical strings of temperature, conductivity, and pressure sensors, deployed on and around the East Flower Garden Bank (EFGB), were used to examine surface wave effects on high-frequency flows over the bank and to quantify spatial and temporal characteristic of these high-frequency flows. The EFGB, about 5-km wide and 10-km long, is located about 180-km southeast of Galveston, Texas, and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface. Three-dimensional flows with frequencies ranging from 0.2 to 2 cycles per hour (cph) were observed in the mixed layer when wind speed and Stokes drift at the surface were large. These motions were stronger over the bank than outside the perimeter. The squared vertical velocity w2 was strongest near the surface and decayed exponentially with depth, and the e-folding length of w2 was 2 times larger than that of Stokes drift. The 2-h-averaged w2 in the mixed layer, scaled by the squared friction velocity, was largest when the turbulent Langmuir number was less than unity and the mixed layer was shallow. It is suggested that Langmuir circulation is responsible for the generation of vertical flows in the mixed layer, and that the increase in kinetic energy is due to an enhancement of Stokes drift by wave focusing. The lack of agreement with open-ocean Langmuir scaling arguments is likely due to the enhanced kinetic energy by wave focusing.

scholarly journals Surface Wave Effects on the Wind-Power Input to Mixed Layer Near-Inertial Motions

2017 ◽  
Vol 47 (5) ◽  
pp. 1077-1093 ◽  
Author(s):  
Guoqiang Liu ◽  
William Perrie ◽  
Colin Hughes
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Wind Power ◽  
Mixed Layer ◽  
Single Point ◽  
Storm Track ◽  
Power Input ◽  
Momentum Fluxes ◽  
Wave Effects ◽  
Evolving Surface

AbstractOcean surface waves play an essential role in a number of processes that modulate the momentum fluxes through the air–sea interface. In this study, the effects of evolving surface waves on the wind-power input (WPI) to near-inertial motions (NIMs) are examined by using momentum fluxes from a spectral wave model and a simple slab ocean mixed layer model. Single-point numerical experiments show that, without waves, the WPI and the near-inertial kinetic energy (NI-KE) are overestimated by about 20% and 40%, respectively. Globally, the overestimate in WPI is about 10% during 2005–08. The largest surface wave effects occur in the winter storm-track regions in the midlatitude northwestern Atlantic, Pacific, and in the Southern Ocean, corresponding to large inverse wave age and rapidly varying strong winds. A relatively low frequency of occurrence of wind sea is found in the midlatitudes, which implies that the influence of evolving surface waves on WPI is intermittent, occurring less than 10% of the total time but making up the dominant contributions to reductions in WPI. Given the vital role of NIMs in diapycnal mixing at the base of the mixed layer and the deep ocean, the present study suggests that it is necessary to include the effects of surface waves on the momentum flux, for example, in studies of coupled ocean–atmosphere dynamics or climate models.

Surface wave effects on submesoscale fronts and filaments

2018 ◽  
Vol 843 ◽  
pp. 479-517 ◽  
Author(s):  
James C. McWilliams
Keyword(s):  
Surface Wave ◽  
Turbulent Mixing ◽  
Wind Wave ◽  
Surface Wind ◽  
Stokes Drift ◽  
Momentum Balance ◽  
Surface Wind Stress ◽  
Time Scale Separation ◽  
Complementary Effect ◽  
Wave Effects

A diagnostic analysis is made for the ageostrophic secondary circulation, buoyancy flux and frontogenetic tendency (SCFT) in upper-ocean submesoscale fronts and dense filaments under the combined influences of boundary-layer turbulent mixing, surface wind stress and surface gravity waves. The analysis is based on a momentum-balance approximation that neglects ageostrophic acceleration, and the surface wave effects are represented with a wave-averaged asymptotic theory based on the time scale separation between wave and current evolution. The wave’s Stokes-drift velocity $\boldsymbol{u}_{st}$ induces SCFT effects that are dominant in strong swell with weak turbulent mixing, and they combine with Ekman and turbulent thermal wind influences in more general situations near wind–wave equilibrium. The complementary effect of the submesoscale currents on the waves is weak for longer waves near the wind–wave or swell spectrum peak, but it is strong for shorter waves.

scholarly journals Large-Eddy Simulation of Langmuir Turbulence in Pure Wind Seas

2008 ◽  
Vol 38 (7) ◽  
pp. 1542-1562 ◽  
Author(s):  
Ramsey R. Harcourt ◽  
Eric A. D’Asaro
Keyword(s):  
Surface Layer ◽  
Surface Wave ◽  
Mixed Layer ◽  
Wave Spectrum ◽  
Vertical Component ◽  
Phase Speed ◽  
Relative Magnitude ◽  
Stokes Drift ◽  
Wave Age ◽  
Large Eddy

Abstract The scaling of turbulent kinetic energy (TKE) and its vertical component (VKE) in the upper ocean boundary layer, forced by realistic wind stress and surface waves including the effects of Langmuir circulations, is investigated using large-eddy simulations (LESs). The interaction of waves and turbulence is modeled by the Craik–Leibovich vortex force. Horizontally uniform surface stress τ0 and Stokes drift profiles uS(z) are specified from the 10-m wind speed U10 and the surface wave age CP/U10, where CP is the spectral peak phase speed, using an empirical surface wave spectra and an associated wave age–dependent neutral drag coefficient CD. Wave-breaking effects are not otherwise included. Mixed layer depths HML vary from 30 to 120 m, with 0.6 ≤ CP/U10 ≤ 1.2 and 8 m s−1 < U10 < 70 m s−1, thereby addressing most possible oceanic conditions where TKE production is dominated by wind and wave forcing. The mixed layer–averaged “bulk” VKE 〈w2〉/u*2 is equally sensitive to the nondimensional Stokes e-folding depth D*S/HML and to the turbulent Langmuir number Lat = u*/US, where u* = |τ0|/ρw in water density ρw and US = |uS|z=0. Use of a D*S scale-equivalent monochromatic wave does not accurately reproduce the results using a full-surface wave spectrum with the same e-folding depth. The bulk VKE for both monochromatic and broadband spectra is accurately predicted using a surface layer (SL) Langmuir number LaSL = u*/〈uS〉SL, where 〈uS〉SL is the average Stokes drift in a surface layer 0 > z > − 0.2HML relative to that near the bottom of the mixed layer. In the wave-dominated limit LaSL → 0, turbulent vertical velocity scales as wrms ∼ u*La−2/3SL. The mean profile (z) of VKE is characterized by a subsurface peak, the depth of which increases with D*S/HML to a maximum near 0.22HML as its relative magnitude /〈w2〉 decreases. Modestly accurate scalings for these variations are presented. The magnitude of the crosswind velocity convergence scales differently from VKE. These results predict that for pure wind seas and HML ≅ 50 m, 〈w2〉/u*2 varies from less than 1 for young waves at U10 = 10 m s−1 to about 2 for mature seas at winds greater than U10 = 30 m s−1. Preliminary comparisons with Lagrangian float data account for invariance in 〈w2〉/u*2 measurements as resulting from an inverse relationship between U10 and CP/U10 in observed regimes.

scholarly journals Langmuir–Submesoscale Interactions: Descriptive Analysis of Multiscale Frontal Spindown Simulations

2014 ◽  
Vol 44 (9) ◽  
pp. 2249-2272 ◽  
Author(s):  
Peter E. Hamlington ◽  
Luke P. Van Roekel ◽  
Baylor Fox-Kemper ◽  
Keith Julien ◽  
Gregory P. Chini
Keyword(s):  
Surface Wave ◽  
Mixed Layer ◽  
Potential Vorticity ◽  
Mixed Layer Depth ◽  
Descriptive Analysis ◽  
Boussinesq Equations ◽  
Stokes Drift ◽  
Small Scale ◽  
Langmuir Turbulence ◽  
Layer Depth

Abstract The interactions between boundary layer turbulence, including Langmuir turbulence, and submesoscale processes in the oceanic mixed layer are described using large-eddy simulations of the spindown of a temperature front in the presence of submesoscale eddies, winds, and waves. The simulations solve the surface-wave-averaged Boussinesq equations with Stokes drift wave forcing at a resolution that is sufficiently fine to capture small-scale Langmuir turbulence. A simulation without Stokes drift forcing is also performed for comparison. Spatial and spectral properties of temperature, velocity, and vorticity fields are described, and these fields are scale decomposed in order to examine multiscale fluxes of momentum and buoyancy. Buoyancy flux results indicate that Langmuir turbulence counters the restratifying effects of submesoscale eddies, leading to small-scale vertical transport and mixing that is 4 times greater than in the simulations without Stokes drift forcing. The observed fluxes are also shown to be in good agreement with results from an asymptotic analysis of the surface-wave-averaged, or Craik–Leibovich, equations. Regions of potential instability in the flow are identified using Richardson and Rossby numbers, and it is found that mixed gravitational/symmetric instabilities are nearly twice as prevalent when Langmuir turbulence is present, in contrast to simulations without Stokes drift forcing, which are dominated by symmetric instabilities. Mixed layer depth calculations based on potential vorticity and temperature show that the mixed layer is up to 2 times deeper in the presence of Langmuir turbulence. Differences between measures of the mixed layer depth based on potential vorticity and temperature are smaller in the simulations with Stokes drift forcing, indicating a reduced incidence of symmetric instabilities in the presence of Langmuir turbulence.

scholarly journals Wave-turbulence scaling in the ocean mixed layer

2012 ◽  
Vol 9 (6) ◽  
pp. 3761-3793
Author(s):  
G. Sutherland ◽  
K. H. Christensen ◽  
B. Ward
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Stokes Drift ◽  
Near Surface ◽  
Oceanic Boundary Layer

Abstract. Microstructure measurements were collected using an autonomous freely rising profiler under a variety of different atmospheric forcing and sea states in the open ocean. Here, profiles of turbulent kinetic energy dissipation rate, ε, are compared with various proposed scalings. In the oceanic boundary layer, the depth dependence of ε was found to be consistent with that expected for a purely shear-driven wall layer. This is in contrast with many recent studies which suggest higher rates of turbulent kinetic energy dissipation in the near surface of the ocean. However, many dissipation profiles scaled with a Stokes drift-generated shear, suggesting there may be occasions where the shear in the mixed layer are dominated by wave-induced currents, which often causes turbulence to extend beyond the mixed layer depth. Integrating ε in the mixed layer yielded results that 1% of the wind power referenced to 10 m is being dissipated here.

scholarly journals Rapid Mixed Layer Deepening by the Combination of Langmuir and Shear Instabilities: A Case Study

2010 ◽  
Vol 40 (11) ◽  
pp. 2381-2400 ◽  
Author(s):  
Tobias Kukulka ◽  
Albert J. Plueddemann ◽  
John H. Trowbridge ◽  
Peter P. Sullivan
Keyword(s):  
Mixed Layer ◽  
Spatial Scales ◽  
Stokes Drift ◽  
Vertical Shear ◽  
Upper Ocean ◽  
Temperature Perturbation ◽  
Langmuir Circulation ◽  
Wind Event ◽  
Shear Instabilities ◽  
Upper Ocean Response

Abstract Langmuir circulation (LC) is a turbulent upper-ocean process driven by wind and surface waves that contributes significantly to the transport of momentum, heat, and mass in the oceanic surface layer. The authors have previously performed a direct comparison of large-eddy simulations and observations of the upper-ocean response to a wind event with rapid mixed layer deepening. The evolution of simulated crosswind velocity variance and spatial scales, as well as mixed layer deepening, was only consistent with observations if LC effects are included in the model. Based on an analysis of these validated simulations, in this study the fundamental differences in mixing between purely shear-driven turbulence and turbulence with LC are identified. In the former case, turbulent kinetic energy (TKE) production due to shear instabilities is largest near the surface, gradually decreasing to zero near the base of the mixed layer. This stands in contrast to the LC case in which at middepth range TKE production can be dominated by Stokes drift shear. Furthermore, the Eulerian mean vertical shear peaks near the base of the mixed layer so that TKE production by mean shear flow is elevated there. LC transports horizontal momentum efficiently downward leading to an along-wind velocity jet below LC downwelling regions at the base of the mixed layer. Locally enhanced vertical shear instabilities as a result of this jet efficiently erode the thermocline. In turn, enhanced breaking internal waves inject cold deep water into the mixed layer, where LC currents transport temperature perturbation advectively. Thus, LC and locally generated shear instabilities work intimately together to facilitate strongly the mixed layer deepening process.

A single dataset Joint Domain Localized Algorithm for clutter suppression in shipborne High Frequency Surface Wave Radar

2020 ◽  
Author(s):  
Liang Guo ◽  
Xin Zhang ◽  
Qiang Yang ◽  
Lin Wang ◽  
Jiazhi Zhang ◽  
...  
Keyword(s):  
Surface Wave ◽  
High Frequency ◽  
Clutter Suppression ◽  
Wave Radar ◽  
Localized Algorithm ◽  
Single Dataset

Multiple Targets Tracking with Compact High-Frequency Surface Wave Radar

2020 ◽  
Author(s):  
Xianpu Zeng ◽  
Mengmeng Zhang ◽  
Hui Zhang
Keyword(s):  
Surface Wave ◽  
High Frequency ◽  
Multiple Targets ◽  
Wave Radar

Recent advances in high-frequency surface-wave methods

2015 ◽  
Author(s):  
Jianghai Xia ◽  
Lingli Gao ◽  
Yudi Pan ◽  
Chao Shen
Keyword(s):  
Surface Wave ◽  
High Frequency ◽  
Recent Advances ◽  
Wave Methods
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