scholarly journals Observations of the Transfer of Energy and Momentum to the Oceanic Surface Boundary Layer beneath Breaking Waves

2016 ◽  
Vol 46 (6) ◽  
pp. 1823-1837 ◽  
Author(s):  
Malcolm E. Scully ◽  
John H. Trowbridge ◽  
Alexander W. Fisher
Keyword(s):  
Vertical Velocity ◽  
Wave Breaking ◽  
Momentum Flux ◽  
Surface Flux ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Wave Band ◽  
Surface Boundary Layer ◽  
Order Of Magnitude ◽  
Energy And Momentum

AbstractMeasurements just beneath the ocean surface demonstrate that the primary mechanism by which energy from breaking waves is transmitted into the water column is through the work done by the covariance of turbulent pressure and velocity fluctuations. The convergence in the vertical transport of turbulent kinetic energy (TKE) balances the dissipation rate of TKE at first order and is nearly an order of magnitude greater than the sum of the integrated Eulerian and Stokes shear production. The measured TKE transport is consistent with a simple conceptual model that assumes roughly half of the surface flux of TKE by wave breaking is transmitted to depths greater than the significant wave height. During conditions when breaking waves are inferred, the direction of momentum flux is more aligned with the direction of wave propagation than with the wind direction. Both the energy and momentum fluxes occur at frequencies much lower than the wave band, consistent with the time scales associated with wave breaking. The largest instantaneous values of momentum flux are associated with strong downward vertical velocity perturbations, in contrast to the pressure work, which is associated with strong drops in pressure and upward vertical velocity perturbations.

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.

Wave Breaking and Ocean Surface Layer Thermal Response

2004 ◽  
Vol 34 (3) ◽  
pp. 693-698 ◽  
Author(s):  
George Mellor ◽  
Alan Blumberg
Keyword(s):  
Surface Layer ◽  
Wave Breaking ◽  
Thermal Response ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Surface Temperatures ◽  
Charnock Constant ◽  
Ocean Surface Layer

Abstract The effect of breaking waves on ocean surface temperatures and surface boundary layer deepening is investigated. The modification of the Mellor–Yamada turbulence closure model by Craig and Banner and others to include surface wave breaking energetics reduces summertime surface temperatures when the surface layer is relatively shallow. The effect of the Charnock constant in the relevant drag coefficient relation is also studied.

scholarly journals Sea spray aerosol as a unique source of ice nucleating particles

2015 ◽  
Vol 113 (21) ◽  
pp. 5797-5803 ◽  
Author(s):  
Paul J. DeMott ◽  
Thomas C. J. Hill ◽  
Christina S. McCluskey ◽  
Kimberly A. Prather ◽  
Douglas B. Collins ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Strong Increase ◽  
Sea Spray ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Surface Areas ◽  
Order Of Magnitude ◽  
Sea Spray Aerosol

Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratory-generated SSA, when normalized to typical total aerosol number concentrations in the marine boundary layer, agree well with measurements from diverse regions over the oceans. Data in the present study are also in accord with previously published INP measurements made over remote ocean regions. INP number concentrations active within liquid water droplets increase exponentially in number with a decrease in temperature below 0 °C, averaging an order of magnitude increase per 5 °C interval. The plausibility of a strong increase in SSA INP emissions in association with phytoplankton blooms is also shown in laboratory simulations. Nevertheless, INP number concentrations, or active site densities approximated using “dry” geometric SSA surface areas, are a few orders of magnitude lower than corresponding concentrations or site densities in the surface boundary layer over continental regions. These findings have important implications for cloud radiative forcing and precipitation within low-level and midlevel marine clouds unaffected by continental INP sources, such as may occur over the Southern Ocean.

scholarly journals Observations of Turbulence in the Ocean Surface Boundary Layer: Energetics and Transport

2009 ◽  
Vol 39 (5) ◽  
pp. 1077-1096 ◽  
Author(s):  
Gregory P. Gerbi ◽  
John H. Trowbridge ◽  
Eugene A. Terray ◽  
Albert J. Plueddemann ◽  
Tobias Kukulka
Keyword(s):  
Boundary Layer ◽  
Diffusion Coefficient ◽  
Kinetic Energy ◽  
Wave Breaking ◽  
Ocean Surface ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Rigid Boundary ◽  
Surface Boundary Layer ◽  
Buoyancy Forcing

Abstract Observations of turbulent kinetic energy (TKE) dynamics in the ocean surface boundary layer are presented here and compared with results from previous observational, numerical, and analytic studies. As in previous studies, the dissipation rate of TKE is found to be higher in the wavy ocean surface boundary layer than it would be in a flow past a rigid boundary with similar stress and buoyancy forcing. Estimates of the terms in the turbulent kinetic energy equation indicate that, unlike in a flow past a rigid boundary, the dissipation rates cannot be balanced by local production terms, suggesting that the transport of TKE is important in the ocean surface boundary layer. A simple analytic model containing parameterizations of production, dissipation, and transport reproduces key features of the vertical profile of TKE, including enhancement near the surface. The effective turbulent diffusion coefficient for heat is larger than would be expected in a rigid-boundary boundary layer. This diffusion coefficient is predicted reasonably well by a model that contains the effects of shear production, buoyancy forcing, and transport of TKE (thought to be related to wave breaking). Neglect of buoyancy forcing or wave breaking in the parameterization results in poor predictions of turbulent diffusivity. Langmuir turbulence was detected concurrently with a fraction of the turbulence quantities reported here, but these times did not stand out as having significant differences from observations when Langmuir turbulence was not detected.

Direct numerical simulation of wind turbulence over breaking waves

2018 ◽  
Vol 850 ◽  
pp. 120-155 ◽  
Author(s):  
Zixuan Yang ◽  
Bing-Qing Deng ◽  
Lian Shen
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Wave Breaking ◽  
Momentum Flux ◽  
Breaking Waves ◽  
Wave Age ◽  
Wave Surface ◽  
Turbulence Statistics ◽  
Large Wave ◽  
Wind Turbulence

We study wind turbulence over breaking waves based on direct numerical simulation (DNS) of two-fluid flows. In the DNS, the air and water are simulated as a coherent system, with the interface captured using the coupled level-set and volume-of-fluid method. Because the wave breaking is an unsteady process, we use ensemble averaging over 100 runs to define turbulence statistics. We focus on analysing the turbulence statistics of the airflow over breaking waves. The effects of wave age and wave steepness are investigated. It is found that before wave breaking, the turbulence statistics are largely influenced by the wave age. The vertical gradient of mean streamwise velocity is positive at small and intermediate wave ages, but it becomes negative near the wave surface at large wave age as the pressure force changes from drag to thrust. Furthermore, wave-coherent motions make increasingly important contributions to the momentum flux and kinetic energy of velocity fluctuations (KE-F) as the wave age increases. During the wave breaking process, spilling breakers do not influence the wind field significantly; in contrast, plunging breakers alter the structures of wind turbulence near the wave surface drastically. It is observed from the DNS results that during wave plunging, a high pressure region occurs ahead of the wave front, which further accelerates the wind in the downstream direction. Meanwhile, a large spanwise vortex is generated, which greatly disturbs the airflow around it, resulting in large magnitudes of Reynolds stress and turbulence kinetic energy (TKE) below the wave crest. Above the crest, the magnitude of KE-F is enhanced during wave plunging at small and large wave ages, but at intermediate wave age, the transient enhancement of KE-F is absent. The effect of wave breaking on the magnitude of KE-F is further investigated through the analysis of the KE-F production. It is discovered that at small wave age, the transient enhancement of KE-F is caused by the appearance of a local maximum in the profile of total momentum flux; but at large wave age, it results from the change in the sign of the KE-F production from negative to positive, due to the sign change in the wave-coherent momentum flux. At intermediate wave age, neither of these two processes is present, and the transient growth of KE-F does not take place.

Energy and momentum flux around comet 67P throughout the Rosetta mission

2020 ◽  
Author(s):  
Hans Nilsson ◽  
Hayley Williamson ◽  
Gabriella Stenberg Wieser ◽  
Ingo Richter ◽  
Charlotte Götz
Keyword(s):  
Solar Wind ◽  
Energy Flux ◽  
Momentum Flux ◽  
Population Based ◽  
Ion Fluxes ◽  
Relative Contribution ◽  
Rosetta Mission ◽  
Order Of Magnitude ◽  
Energy And Momentum ◽  
Comet 67P

<p>We calculate the momentum and energy flux of ions measured by the Ion Composition Analyzer (ICA) on the Rosetta mission at comet 67P/Churyumov-Gerasimenko. We find that the total ion energy and momentum flux stay roughly constant over the mission, but the relative contribution of solar wind ions and cometary ions changes drastically depending on the spacecraft position in the ionosphere and distance from the comet to the sun. We also see that the magnetic pressure, calculated from the magnetic field measured by the Rosetta magnetometer, is on the order of the total ion momentum flux and roughly corresponds with the cometary ion momentum flux. Near both the beginning and end of the mission, solar wind momentum and energy flux are roughly two orders of magnitude larger than the corresponding heavy cometary ion fluxes. When the spacecraft enters the solar wind ion cavity near the comet’s periapsis, the solar wind energy and momentum flux drop drastically, mainly due to reduced density. Meanwhile, the cometary energy flux increases to be roughly equal to the solar wind flux earlier in the mission and the cometary momentum flux as measured by ICA becomes roughly an order of magnitude higher than previous and later solar wind fluxes. We also examine the changes in flux on two excursions, one on the dayside and one on the nightside of the comet, and see that during the nightside excursion, the cometary ion fluxes drop off roughly with the square of the distance from the comet. During the dayside excursion the flux was approximately constant, indicating that the excursion distance was small compared to the region where the observed ions were produced. ICA does not measure the lowest energy ions, so we also discuss the energy and momentum of the full ion population based on density estimates from the LAP and MIP instruments.</p>

Effect of surface wave breaking on the surface boundary layer of temperature in the Yellow Sea in summer

2011 ◽  
Vol 38 (3-4) ◽  
pp. 267-279 ◽  
Author(s):  
Zhang Xuefeng ◽  
Han Guijun ◽  
Wang Dongxiao ◽  
Li Wei ◽  
He Zhongjie
Keyword(s):  
Boundary Layer ◽  
Surface Wave ◽  
Yellow Sea ◽  
Wave Breaking ◽  
The Yellow Sea ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Effect Of Surface

A Comparative Study of Wave Breaking Models in a High-Order Spectral Model

2017 ◽  
Author(s):  
Betsy R. Seiffert ◽  
Guillaume Ducrozet
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Boundary Conditions ◽  
Wave Breaking ◽  
Water Surface ◽  
Eddy Viscosity ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Diffusion Term ◽  
Surface Boundary Conditions

We examine the implementation of two different wave breaking models into the nonlinear potential flow solver HOS-NWT. HOS-NWT is a computationally efficient, open source code that solves for surface elevation in a numerical wave tank using the High-Order Spectral (HOS) method [1]. The first model is a combination of a kinematic wave breaking onset criteria proposed by Barthelemey, et al. [2] and validated by Saket, et al. [3], and an energy dissipation mechanism proposed by Tian, et al. [4, 5]. The wave breaking onset parameter is based on the ratio of local energy flux velocity to the local crest velocity. Once breaking is initiated, an eddy viscosity parameter is estimated based on the pre-breaking local wave geometry, as described in [4, 5]. This eddy viscosity is then added as a diffusion term to the kinematic and dynamic free surface boundary conditions for the duration of wave breaking. Results implementing this wave breaking mechanism in HOS-NWT have shown that the model can successfully calculate the surface elevation and corresponding frequency spectra, as well as the energy dissipation associated with breaking waves [6–8]. The second model implemented to account for wave breaking in HOS-NWT is based on the method proposed by Chalikov, et al. [9–11]. This model defines wave breaking onset by the curvature of the water surface and defines the wave as broken if it exceeds a certain value. A diffusion term is added to the kinematic and dynamic free surface boundary conditions which dissipates energy based on the local curvature of the water surface, which is consequently not constant in space nor time. Calculations made using the two models are compared with large scale experimental measurements conducted at the Hydrodynamics, Energetics and Atmospheric Environment Lab (LHEEA) at Ecole Centrale de Nantes. Comparison of calculations with measurements suggest that both models are successful at predicting wave breaking onset and energy dissipation. However, the model proposed by Barthelemy, et al. [2] and Tian, et al. [4] can be applied without knowing anything about the breaking waves a priori, whereas the model proposed by Chalikov [9] requires tuning to specific conditions.

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.

Sign in / Sign up

Export Citation Format

Share Document