Breaking waves and their effects on near surface sound speed

2002 ◽  
Author(s):  
E. Terrill ◽  
K. Melville
Keyword(s):  
Sound Speed ◽  
Breaking Waves ◽  
Near Surface

scholarly journals Field Measurements of Surface and Near-Surface Turbulence in the Presence of Breaking Waves

2015 ◽  
Vol 45 (4) ◽  
pp. 943-965 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Field Experiments ◽  
North Pacific Ocean ◽  
Large Fraction ◽  
Field Measurements ◽  
Breaking Waves ◽  
Sea Surface ◽  
Near Surface ◽  
Wave Energy Dissipation ◽  
Eddy Simulation ◽  
The North

AbstractWave breaking removes energy from the surface wave field and injects it into the upper ocean, where it is dissipated by viscosity. This paper presents an investigation of turbulent kinetic energy (TKE) dissipation beneath breaking waves. Wind, wave, and turbulence data were collected in the North Pacific Ocean aboard R/P FLIP, during the ONR-sponsored High Resolution Air-Sea Interaction (HiRes) and Radiance in a Dynamic Ocean (RaDyO) experiments. A new method for measuring TKE dissipation at the sea surface was combined with subsurface measurements to allow estimation of TKE dissipation over the entire wave-affected surface layer. Near the surface, dissipation decayed with depth as z−1, and below approximately one significant wave height, it decayed more quickly, approaching z−2. High levels of TKE dissipation very near the sea surface were consistent with the large fraction of wave energy dissipation attributed to non-air-entraining microbreakers. Comparison of measured profiles with large-eddy simulation results in the literature suggests that dissipation is concentrated closer to the surface than previously expected, largely because the simulations did not resolve microbreaking. Total integrated dissipation in the water column agreed well with dissipation by breaking for young waves, (where cm is the mean wave frequency and is the atmospheric friction velocity), implying that breaking was the dominant source of turbulence in those conditions. The results of these extensive measurements of near-surface dissipation over three field experiments are discussed in the context of observations and ocean boundary layer modeling efforts by other groups.

scholarly journals Ocean bubbles under high wind conditions. Part 1: Bubble distribution and development

2021 ◽  
Author(s):  
Helen Czerski ◽  
Ian M. Brooks ◽  
Steve Gunn ◽  
Robin Pascal ◽  
Adrian Matei ◽  
...  
Keyword(s):  
Void Fraction ◽  
Breaking Waves ◽  
Surface Flow ◽  
Stokes Drift ◽  
Gas Transfer ◽  
Langmuir Circulation ◽  
Near Surface ◽  
Wind Speeds ◽  
Void Fractions ◽  
Bubble Plumes

Abstract. The bubbles generated by breaking waves are of considerable scientific interest due to their influence on air-sea gas transfer, aerosol production, and upper ocean optics and acoustics. However, a detailed understanding of the processes creating deeper bubble plumes (extending 2–10 metres below the ocean surface) and their significance for air-sea gas exchange is still lacking. Here, we present bubble measurements from the HiWinGS expedition in the North Atlantic in 2013, collected during several storms with wind speeds of 10–27 m s−1. A suite of instruments was used to measure bubbles from a self-orienting free-floating spar buoy: a specialised bubble camera, acoustical resonators, and an upward-pointing sonar. The focus in this paper is on bubble void fractions and plume structure. The results are consistent with the presence of a heterogeneous shallow bubble layer occupying the top 1–2 m of the ocean which is regularly replenished by breaking waves, and deeper plumes which are only formed from the shallow layer at the convergence zones of Langmuir circulation. These advection events are not directly connected to surface breaking. The void fraction distributions at 2 m depth show a sharp cut-off at a void fraction of 10−4.5 even in the highest winds, implying the existence of mechanisms limiting the void fractions close to the surface. Below wind speeds of 16 m s−1 or RHw = 2 × 106, the probability distribution of void fraction at 2 m depth is very similar in all conditions, but increases significantly above either threshold. Void fractions are significantly different during periods of rising and falling winds, but there is no distinction with wave age. There is a complex near-surface flow structure due to Langmuir circulation, Stokes drift, and wind-induced current shear which influences the spatial distribution of bubbles within the top few metres. We do not see evidence for slow bubble dissolution as bubbles are carried downwards, implying that collapse is the more likely termination process. We conclude that the shallow and deeper bubble layers need to be studied simultaneously to link them to the 3D flow patterns in the top few metres of the ocean. Many open questions remain about the extent to which deep bubble plumes contribute to air-sea gas transfer. A companion paper (Czerski, 2021) addresses the observed bubble size distributions and the processes responsible for them.

scholarly journals Coastal Aerosol Profiling with a Camera Lidar and Nephelometer

2011 ◽  
Vol 28 (3) ◽  
pp. 418-425 ◽  
Author(s):  
N. C. Parikh Sharma ◽  
John E. Barnes ◽  
Trevor B. Kaplan ◽  
Antony D. Clarke
Keyword(s):  
Boundary Layer ◽  
Phase Function ◽  
Marine Boundary Layer ◽  
Breaking Waves ◽  
Aerosol Sampling ◽  
Near Surface ◽  
Average Value ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Wide Angle Camera

Abstract A bistatic lidar configuration of a wide-angle camera (100°) and vertically pointed laser (532 nm) was used to profile aerosols at a coastal site. Aerosol profiles were measured on two evenings from the surface through the boundary layer. The site, on the eastern tip of the Big Island of Hawaii, is influenced by both marine boundary layer aerosols and breaking waves. Two nephelometers, located at 7 and 25 m above sea level, were compared directly with the 0.5-m-altitude resolution of the camera lidar (clidar). At 7 m, changes in aerosol were tracked quite well by the clidar. At 25 m the aerosol was fairly constant and a useful comparison could only be made with averaged values. The clidar results showed a steep gradient (decreasing with altitude) in the aerosol extinction from 7 to about 35 m. The gradient continued to 200 m at a lower rate. This demonstrated the use of the clidar in characterizing the environment for the in situ aerosol sampling. Both a measured and a NASA Aerosol Robotic Network (AERONET)-derived aerosol phase function, representing similar marine conditions but from different locations, were used to convert the single-angle clidar scatter to extinction. The measured function gave the best fit to the near-surface nephelometer data. The extinction/backscatter ratio, derived by comparing the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth to the integrated clidar profile, was higher than the long-term average value from the AERONET aerosol phase function.

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 Effects of Wave Breaking on the Near-Surface Profiles of Velocity and Turbulent Kinetic Energy

2004 ◽  
Vol 34 (2) ◽  
pp. 490-504 ◽  
Author(s):  
Arne Melsom ◽  
Øyvind SÆtra
Keyword(s):  
Surface Stress ◽  
Wave Breaking ◽  
Traditional Approach ◽  
Surface Region ◽  
Breaking Waves ◽  
Stokes Drift ◽  
Surface Velocity ◽  
Momentum Exchange ◽  
Near Surface ◽  
The Mean

Abstract A theoretical model for the near-surface velocity profile in the presence of breaking waves is presented. Momentum is accumulated by growing waves and is released upon wave breaking. In effect, such a transition is a process involving a time-dependent surface stress acting on the mean current. In this paper, conventional theory for the Stokes drift is expanded to fourth-order accuracy in wave steepness. It is shown that the higher-order terms lead to an enhancement of the surface Stokes drift and a slight retardation of the Stokes volume flux. Furthermore, the results from the wave theory are used to obtain a bulk parameterization of momentum exchange during the process of wave breaking. The mean currents are then obtained by application of a variation of the “level 2.5” turbulence closure theory of Mellor and Yamada. When compared with the traditional approach of a constant surface stress, the mean Eulerian current exhibits a weak enhancement in the near-surface region, compensated by a negative shift deeper in the water column. However, it is found that the results of Craig and Banner and the results of Craig are not significantly affected by the present theory. Hence, this study helps to explain why the Craig and Banner model agrees well with observations when a realistic, time-varying surface stress acts on the drift currents.

Detection and Characterization of Microscale Breaking Waves

2003 ◽  
Author(s):  
M. H. Kamran Siddiqui ◽  
Mark R. Loewen
Keyword(s):  
Wind Speed ◽  
Water Surface ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Skin Layer ◽  
Wave Crest ◽  
Gas Transfer ◽  
Near Surface ◽  
Wind Speeds ◽  
The Waves

Microscale breaking waves are short wind-generated waves that break without air entrainment. At low to moderate wind speeds microscale breaking waves play an important role in enhancing air-water heat and gas transfer. We report on a series of experiments conducted in a wind-wave flume at Harris Hydraulics Laboratory (University of Washington, Seattle) designed to investigate the importance of microscale breaking waves in generating near-surface turbulence and in enhancing air-sea gas and heat transfer rates. Non-invasive experiments were performed at wind speeds ranging from 4.5 m/s to 11 m/s and at a fetch of 5.5 m. The skin-layer or water surface temperature was measured using an infrared (IR) imager and digital particle image velocimetry (DPIV) was used to obtain simultaneous measurements of the two-dimensional velocities immediately below the water surface. Analysis of the simultaneous DPIV and infrared datasets revealed that microscale breaking waves generate strong vortices in their crests that disrupt the cool skin layer at the water surface and create thermal wakes that are visible in the infrared images. While non-breaking waves do not generate strong vortices and hence do not disrupt the skin layer. We developed a scheme based on the magnitude of vorticity in the wave crest to identify microscale breaking waves. The results show that at a wind speed of 4.5 m/s, 11% of the waves broke. The percentage of breaking waves increased with wind speed and at a wind speed of 11 m/s, 91% of the waves were microscale breaking waves. Comparison of different geometric and flow properties of microscale breaking and non-breaking waves revealed that microscale breaking waves are steeper, larger in amplitude and generate more turbulent kinetic energy compared to non-breaking waves.

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