scholarly journals Roles of breaking waves and Langmuir circulation in the surface boundary layer of a coastal ocean

2013 ◽  
Vol 118 (10) ◽  
pp. 5173-5187 ◽  
Author(s):  
Shuang Li ◽  
Ming Li ◽  
Gregory P. Gerbi ◽  
Jin-Bao Song
Keyword(s):  
Boundary Layer ◽  
Breaking Waves ◽  
Coastal Ocean ◽  
Surface Boundary ◽  
Langmuir Circulation ◽  
Surface Boundary Layer

scholarly journals Measurements of Enhanced Near-Surface Turbulence under Windrows

2020 ◽  
Vol 50 (1) ◽  
pp. 197-215
Author(s):  
Seth F. Zippel ◽  
Ted Maksym ◽  
Malcolm Scully ◽  
Peter Sutherland ◽  
Dany Dumont
Keyword(s):  
Boundary Layer ◽  
Surface Flux ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Surface Turbulence ◽  
Order Of Magnitude ◽  
Convergence Zones ◽  
Shallow Bay

AbstractObservations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counterrotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

scholarly journals Observations of Turbulence Mixing and Vorticity in a Littoral Surface Boundary Layer

2008 ◽  
Vol 38 (3) ◽  
pp. 648-669 ◽  
Author(s):  
R-C. Lien ◽  
B. Sanford ◽  
W-T. Tsai
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Surface Waves ◽  
Turbulence Kinetic Energy ◽  
Surface Boundary ◽  
Vertical Profiles ◽  
Langmuir Circulation ◽  
Surface Boundary Layer ◽  
Turbulence Mixing ◽  
Shear Turbulence

Abstract Measurements of small-scale vorticity, turbulence velocity, and dissipation rates of turbulence kinetic energy ɛ were taken in a littoral fetch-limited surface wave boundary layer. Drifters deployed on the surface formed convergence streaks with ∼1-m horizontal spacing within a few minutes. In the interior, however, no organized pattern of velocity, vorticity, or turbulence mixing intensity was found at a similar horizontal spatial scale. The turbulent Langmuir number La was 0.6–1.3, much larger than the 0.3 of the typical open ocean, suggesting comparable importance of wind-driven turbulence and Langmuir circulation. Observed ɛ are explained by the wind-driven shear turbulence. The production rate of turbulence kinetic energy associated with the vortex force is about 10−7 W kg−1, slightly smaller than that generated by the wind-driven turbulence. The rms values of the streakwise component of vorticity σζ|| and the vertical component of vorticity σζz have a similar magnitude of ∼0.02 s−1. Vertical profiles of ɛ, σζ||, and σζz showed a monotonic decrease from the surface. Traditionally, surface convergence streaks are regarded as signatures of Langmuir circulation. Two large-eddy simulations with and without Stokes drift were performed. Both simulations produced surface convergence streaks and vertical profiles of ɛ, vorticity, and velocity consistent with observations. The observations and model results suggest that the presence of surface convergence streaks does not necessarily imply the existence of Langmuir circulation. In a littoral surface boundary layer where surface waves are young, fetch-limited, and weak, and La = O(1), the turbulence mixing in the surface mixed layer is primarily due to the wind-driven shear turbulence, and convergence streaks exist with or without surface waves.

scholarly journals The Role of Whitecapping in Thickening the Ocean Surface Boundary Layer

2015 ◽  
Vol 45 (8) ◽  
pp. 2006-2024 ◽  
Author(s):  
Gregory P. Gerbi ◽  
Samuel E. Kastner ◽  
Genevieve Brett
Keyword(s):  
Boundary Layer ◽  
Initial Conditions ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Length Scale ◽  
Surface Boundary ◽  
Transfer Velocity ◽  
Surface Boundary Layer ◽  
Turbulent Length Scale ◽  
Shear Production

AbstractThe effects of wind-driven whitecapping on the evolution of the ocean surface boundary layer are examined using an idealized one-dimensional Reynolds-averaged Navier–Stokes numerical model. Whitecapping is parameterized as a flux of turbulent kinetic energy through the sea surface and through an adjustment of the turbulent length scale. Simulations begin with a two-layer configuration and use a wind that ramps to a steady stress. This study finds that the boundary layer begins to thicken sooner in simulations with whitecapping than without because whitecapping introduces energy to the base of the boundary layer sooner than shear production does. Even in the presence of whitecapping, shear production becomes important for several hours, but then inertial oscillations cause shear production and whitecapping to alternate as the dominant energy sources for mixing. Details of these results are sensitive to initial and forcing conditions, particularly to the turbulent length scale imposed by breaking waves and the transfer velocity of energy from waves to turbulence. After 1–2 days of steady wind, the boundary layer in whitecapping simulations has thickened more than the boundary layer in simulations without whitecapping by about 10%–50%, depending on the forcing and initial conditions.

scholarly journals Parameterization of Wave-Induced Mixing Using the Large Eddy Simulation (LES) (I)

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 207 ◽  
Author(s):  
Haili Wang ◽  
Changming Dong ◽  
Yongzeng Yang ◽  
Xiaoqian Gao
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Global Climate Models ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wave Induced

Turbulent motions in the thin ocean surface boundary layer control exchanges of momentum, heat and trace gases between the atmosphere and ocean. However, present parametric equations of turbulent motions that are applied to global climate models result in systematic or substantial errors in the ocean surface boundary layer. Significant mixing caused by surface wave processes is missed in most parametric equations. A Large Eddy Simulation model is applied to investigate the wave-induced mixed layer structure. In the wave-averaged equations, wave effects are calculated as Stokes forces and breaking waves. To examine the effects of wave parameters on mixing, a series of wave conditions with varying wavelengths and heights are used to drive the model, resulting in a variety of Langmuir turbulence and wave breaking outcomes. These experiments suggest that wave-induced mixing is more sensitive to wave heights than to the wavelength. A series of numerical experiments with different wind intensities-induced Stokes drifts are also conducted to investigate wave-induced mixing. As the wind speed increases, the influence depth of Langmuir circulation deepens. Additionally, it is observed that breaking waves could destroy Langmuir cells mainly at the sea surface, rather than at deeper layers.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals A global perspective on Langmuir turbulence in the ocean surface boundary layer

2012 ◽  
Vol 39 (18) ◽  
Author(s):  
Stephen E. Belcher ◽  
Alan L. M. Grant ◽  
Kirsty E. Hanley ◽  
Baylor Fox-Kemper ◽  
Luke Van Roekel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Global Perspective ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer
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