On the Nature of the Turbulent Energy Dissipation Beneath Nonbreaking Waves

Abstract

Here we have determined the nature of turbulent flow associated with oceanic nonbreaking waves, which are on average much more prevalent than breaking waves in most wind conditions. We found this flow to be characterized by a low turbulence microscale Reynolds number of 30 < Re < 100. We observed that the turbulent kinetic energy dissipation rate associated with nonbreaking waves , ranged to 3 • 10 −4 W/kg for a wave amplitude 50 cm. The , under nonbreaking waves, was consistent with = 2 T (S i) 2 ; S ij is the large-scale (energy-containing scales) wave-induced mean flow stress tensor. The turbulent Reynolds stress associated with nonbreaking waves was consistent with experimental data when parameterized by an amplitude independent constant turbulent eddy viscosity, 10 times larger than the molecular value. Given that nonbreaking waves typically cover a much larger fraction of the ocean surface (90-100%) than breaking waves, this result shows that their contribution to wave dissipation can be significant. Plain Language Summary Considering that surface waves cover most of the ocean, the precise determination of the rate at which surface waves dissipate energy is necessary to properly quantify climate, weather, or ocean dynamic processes at the air-sea interface and within the upper layer of the ocean. The upper-ocean mixing intensity is often related to breaking surface waves, while the turbulence generated by nonbreaking surface waves is poorly understood and thus not well represented. Our laboratory experiments used microstructure and optical measurements to observe micro velocity shears and temperature fluctuations associated with passing nonbreaking solitary surface waves. Here we report measurements of the energy dissipation associated with these nonbreaking surface waves. We present an analytical approach to quantify the nonbreaking wave turbulence strength from large-scale (energy-containing) flow measurements. The analysis by Teixeira and Belcher (2002) demonstrated that the main mechanism responsible for NBSW turbulence is associated with Stokes drift tilting the small-scale vortex structures, followed by their RESEARCH LETTER

Laboratory Quantification of the Relative Contribution of Staghorn Coral Skeletons to the Total Wave-Energy Dissipation Provided by an Artificial Coral Reef

“…WW1 and UDM1 as well as WW2 and UDM2 were paired before and after the reef model to ensure the quality of the signals recorded as UDMs may present errors when wave breaking occurs due to the splash of water in the air. Moreover, having two distinct measurements allows also separating incident and reflected waves [31][32][33]. Figure 3 illustrates the experimental setup for this study with the location of the wave gauges.…”

“…Wave heights calculated following the aforementioned process are, however, biased by wave reflection from the artificial parabolic perforated steel beach present at the end of the SUSTAIN flume. Therefore, in this study, incident and reflected waves are separated numerically from their combined signal following [31,32] as the artificial beach in Filtered water-level data were analyzed according to short-term wave theory to calculate wave heights [37,55]. In short-term wave analysis, wave heights are described as the vertical distance between the maximum (wave crest) and minimum (wave trough) water levels between two successive zero-up or down crossings.…”

“…Wave heights calculated following the aforementioned process are, however, biased by wave reflection from the artificial parabolic perforated steel beach present at the end of the SUSTAIN flume. Therefore, in this study, incident and reflected waves are separated numerically from their combined signal following [31,32] as the artificial beach in SUSTAIN cannot be approximated by typical surfaces and slopes found in literature. The separation process explores the water-level measurements of the combined wave signal from two wave gauges positioned at a distance ∆x from each other with water elevations modeled as two harmonic signals:…”

Asymmetric Frontal Response across the Gulf of Mexico Front in Winter 2016

“…Following the standard assumption that the oceanic flow can be approximated by idealized homogenous and isotropic turbulence, the TKED (or ) can be derived from the VMP200 measured shear spectrum Ψ(K) as [25,26]…”

Observations and Parametrization of the Turbulent Energy Dissipation Beneath Non-Breaking Waves

“…The ν T parametrization in terms of measured flow variables permits the effective inclusion of non-breaking waves in models. The experiments of Bogucki et al [11] demonstrated that within the investigated range of wave amplitudes and wavelengths, ν T ≈ 10ν (ν the water molecular kinematic viscosity). Bogucki et al [11] attributed the observed scatter of ν T to the variability of the background turbulent flow but did not provide a parametrization of ν T .…”