Energy dissipation of wind‐generated waves and whitecap coverage

Hwang, Paul A.; Sletten, Mark A.

doi:10.1029/2007jc004277

Cited by 61 publications

(71 citation statements)

References 35 publications

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“…This threshold for spume production is significantly greater than the value of (0.013 to 0.038 Wm À2 ) for whitecap fraction found by Hwang and Sletten [2008]. This is consistent with observations that the wind speed threshold for whitecapping is lower than for spume droplet production.…”

Section: Analysis Of Breaking Surface Energy Fluxsupporting

confidence: 76%

Investigation of the physical scaling of sea spray spume droplet production

Fairall¹,

Banner²,

Peirson³

et al. 2009

J. Geophys. Res.

104

129

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[1] In this paper we report on a laboratory study, the Spray Production and Dynamics Experiment (SPANDEX), conducted at the University of New South Wales Water Research Laboratory in Australia. The goals of SPANDEX were to illuminate physical aspects of spume droplet production and dispersion; verify theoretical simplifications used to estimate the source function from ambient droplet concentration measurements; and examine the relationship between the implied source strength and forcing parameters such as wind speed, surface turbulent stress, and wave properties. Observations of droplet profiles give reasonable confirmation of the basic power law profile relationship that is commonly used to relate droplet concentrations to the surface source strength. This essentially confirms that, even in a wind tunnel, there is a near balance between droplet production and removal by gravitational settling. The observations also indicate considerable droplet mass may be present for sizes larger than 1.5 mm diameter. Phase Doppler Anemometry observations revealed significant mean horizontal and vertical slip velocities that were larger closer to the surface. The magnitude seems too large to be an acceleration time scale effect. Scaling of the droplet production surface source strength proved to be difficult. The wind speed forcing varied only 23% and the stress increased a factor of 2.2. Yet, the source strength increased by about a factor of 7. We related this to an estimate of surface wave energy flux through calculations of the standard deviation of small-scale water surface disturbance, a wave-stress parameterization, and numerical wave model simulations. This energy index only increased by a factor of 2.3 with the wind forcing. Nonetheless, a graph of spray mass surface flux versus surface disturbance energy is quasi-linear with a substantial threshold.

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Section: Analysis Of Breaking Surface Energy Fluxsupporting

confidence: 76%

Investigation of the physical scaling of sea spray spume droplet production

Fairall¹,

Banner²,

Peirson³

et al. 2009

J. Geophys. Res.

104

129

View full text Add to dashboard Cite

show abstract

“…The whitecap coverage fraction obtained from such imagery routinely serves as a basis for parameterizations of a variety of air-sea exchange processes, including the turbulent dissipation rate in the upper ocean [5]. Additionally, visible imagery often reveals the tendency for surface foam and bubbles to congregate in long streaks or windrows.…”

Section: Visible Light Methodsmentioning

confidence: 99%

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

et al. 2018

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This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1-14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.Keywords: airborne remote sensing; ocean surface currents; upper ocean turbulence BackgroundCapabilities for spatial measurements of ocean surface turbulence are highly desirable for a wide variety of needs ranging from basic studies of upper ocean mixing processes to data assimilation into high-resolution coastal and ocean circulation models. On the global scale, presently available observations of the ocean currents are provided by satellite altimeters, which are limited to mesoscales and resolve only the geostrophic component of the surface current. Much anticipated launches of the

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“…The net wave growth is controlled by the wind input and wave-breaking dissipation terms because the nonlinear waveÁwave interaction only causes energy exchange among wave spectral components. It has been shown that the net wave growth is one order of magnitude smaller than the wind input (Hasselmann et al, 1973;Resio, 1981;Hwang and Sletten, 2008). To the firstorder approximation, we scale F with R dis (R dis 0r w F), and eq.…”

Section: Turbulent Dissipation Rate In Wave-breaking Layermentioning

confidence: 99%

“…Attempts have been made to relate the breaking wave-energy dissipation rates to both wind and wave parameters (Guan et al, 2007;Hwang and Sletten, 2008;Kitaigorodskii, 2009). Zhao and Toba (2001), suggesting that the windÁsea Reynolds number R B is an effective parameter describing the breaking wave characteristics in terms of whitecap coverage.…”

Section: Turbulent Dissipation Rate In Wave-breaking Layermentioning

confidence: 99%

Gas transfer velocity in the presence of wave breaking

Zhao

2016

Tellus B: Chemical and Physical Meteorology

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A B S T R A C T Wave breaking is known to cause air entrainment and enhancement of the near-surface turbulence. Thus, it intensifies the gas exchange across the airÁsea interface. Based on the combination of the vertical distribution of the turbulence in the wave-affected layer and the breaking wave-energy dissipation rate in the wave-breaking layer, we proposed a composite model for the gas transfer velocity in the presence of wave breaking. The gas transfer velocity was calculated as a function of the air frictional velocity, wave age, and whitecap coverage. The model was validated by the dependences on winds and wave ages by field and laboratory measurements. The results supported the hypothesis that the large uncertainties in the traditional gas transfer velocities based on wind speed alone at moderate-to-high wind speeds can be ascribed to the neglect of the windÁwave effect, which is mainly attributed to the whitecap coverage as a function of the windÁsea Reynolds number.

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Energy dissipation of wind‐generated waves and whitecap coverage

Cited by 61 publications

References 35 publications

Investigation of the physical scaling of sea spray spume droplet production

Investigation of the physical scaling of sea spray spume droplet production

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

Gas transfer velocity in the presence of wave breaking

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