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Bubbles directly link sea surface structure to the dissipation rate of turbulence in the ocean surface layer through wave breaking, and they are an important vehicle for air–sea transfer of heat and gases and important for understanding both hurricanes and global climate. Adequate parameterization of bubble dynamics, especially in high winds, requires simultaneous measurements of surface waves and breaking-induced turbulence; collection of such data would be hazardous in the field, and they are largely absent from laboratory studies to date. We therefore present data from a series of laboratory wind-wave tank experiments designed to observe bubble size distributions in natural seawater beneath hurricane conditions and connect them to surface wave statistics and subsurface turbulence. A shadowgraph imager was used to observe bubbles in three different water temperature conditions. We used these controlled conditions to examine the role of stability, surface tension, and water temperature on bubble distributions. Turbulent kinetic energy dissipation rates were determined from subsurface ADCP data using a robust inertial-subrange identification algorithm and related to wind input via wave-dependent scaling. Bubble distributions shift from narrow to broadbanded and toward smaller radius with increased wind input and wave steepness. TKE dissipation rate and shear were shown to increase with wave steepness; this behavior is associated with a larger number of small bubbles in the distributions, suggesting shear is dominant in forcing bubbles in hurricane wind-wave conditions. These results have important implications for bubble-facilitated air–sea exchanges, near-surface ocean mixing, and the distribution of turbulence beneath the air–sea interface in hurricanes. Significance Statement: Bubbles are a vehicle for the flux of heat, momentum, and gases between the atmosphere and ocean. These fluxes contribute to the energy budgets of hurricanes, climate, and upper-ocean biology. Few to no simultaneous measurements of surface waves, bubbles, and turbulence have been made in hurricane conditions. To improve numerical model representation of bubbles, we performed laboratory experiments to parameterize bubble size distributions using physical variables including wind and waves. Bubble distributions were found to become broadbanded and shift toward smaller radius with increased wind stress and wave steepness. Turbulence dissipation rate and shear were shown to increase with wave steepness. Our results give the first physically based bubble distribution parameterization from naturally breaking waves in hurricane-force conditions. [ABSTRACT FROM AUTHOR]

Here, for non-breaking short surface waves, we have experimentally determined the value of the turbulent eddy viscosity ν T or its ratio ν T * ≡ ν T / ν , where ν is the water kinematic viscosity. The non-breaking wave-generated turbulent eddy viscosity ν T was found to depend on the ratio of the wave period, T, to the microscale Kolmogorov time scale, τ η . Our observations were consistent with ν T * = 1.46 · (T / τ η) − 2.6 when (T / τ η) < 0.9 . That implied that the ν T * ∝ ϵ − 1.3 , where ϵ is the background turbulent energy dissipation rate. The near-surface turbulent flow associated with non-breaking waves was characterized by a short inertial subrange. The background turbulence appears to modulate the amount of energy the non-breaking waves dissipate locally and, consequently, the wave's decay rate. Our results imply that the background turbulent flow acts as a lubricant, permitting waves to propagate further when traveling over a more energetic turbulent background flow. Our results have implications for the modeling of oceanic wave propagation or the air–sea exchange processes. [ABSTRACT FROM AUTHOR]

Short-range infrared (IR) observations of ocean surface reveal complicated spatially varying and evolving structures. Here we present an approach to use spatially correlated time series IR images, over a time scale of one-tenth of a second, of the water surface to derive underlying surface velocity and turbulence fields. The approach here was tested in a laboratory using grid-generated turbulence and a heater assembly. The technique was compared with in situ measurements to validate our IR-derived remotemeasurements. The IR-measured turbulent kinetic energy (TKE) dissipation rateswere consistent with in situ--measured dissipation using a vertical microstructure profiler (VMP). We used measurements of the gradient of the velocity field to calculate TKE dissipation rates at the surface. Based on theoretical and experimental considerations, we have proposed two models of IR TKE dissipation rate retrievals and designed an approach for oceanic field IR applications. [ABSTRACT FROM AUTHOR]

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 < Reλ < 100. We observed that the turbulent kinetic energy dissipation rate associated with nonbreaking waves ϵ, ranged to 3 · 10−4 W/kg for a wave amplitude 50 cm. The ϵ, under nonbreaking waves, was consistent with ϵ=2νTSij2; Sij 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. Key Points: Nonbreaking surface waves magnify background turbulent fluctuationsNonbreaking wave‐enhanced turbulence is characterized by a relatively low Reynolds numberThe dissipation caused by nonbreaking waves is proportional to the square of the mean wave flow stress tensor [ABSTRACT FROM AUTHOR]

This study analyzes high-resolution ship data collected in the Gulf of Mexico during the Lagrangian Submesoscale Experiment (LASER) from January to February 2016 to produce the first reported measurements of dissipative heating in the explicitly nonhurricane atmospheric surface layer. Although typically computed from theory as a function of wind speed cubed, the dissipative heating directly estimated via the turbulent kinetic energy (TKE) dissipation rate is also presented. The dissipative heating magnitude agreed with a previous study that estimated the dissipative heating in the hurricane boundary layer using in situ aircraft data. Our observations that the 10-m neutral drag coefficient parameterized using TKE dissipation rate approaches zero slope as wind increases suggests that TKE dissipation and dissipative heating are constrained to a physical limit. Both surface-layer stability and sea state were observed to be important conditions influencing dissipative heating, with the stability determined via TKE budget terms and the sea state determined via wave steepness and age using direct shipboard measurements. Momentum and enthalpy fluxes used in the TKE budget are determined using the eddy-correlation method. It is found that the TKE dissipation rate and the dissipative heating are largest in a nonneutral atmospheric surface layer with a sea surface comprising steep wind sea and slow swell waves at a given surface wind speed, whereas the ratio of dissipative heating to enthalpy fluxes is largest in near-neutral stability where the turbulent vertical velocities are near zero. [ABSTRACT FROM AUTHOR]

This paper is dedicated to wave-induced turbulence unrelated to wave breaking. The existence of such turbulence has been foreshadowed in a number of experimental, theoretical, and numerical studies. The current study presents direct measurements of this turbulence. The laboratory experiment was conducted by means of particle image velocimetry, which allowed estimates of wavenumber velocity spectra beneath monochromatic nonbreaking unforced waves. Observed spectra intermittently exhibited the Kolmogorov interval associated with the presence of isotropic turbulence. The magnitudes of the energy dissipation rates due to this turbulence in the particular case of 1.5-Hz deep-water waves were quantified as a function of the surface wave amplitude. The presence of such turbulence, previously not accounted for, can affect the physics of the wave energy dissipation, the subsurface boundary layer, and the ocean mixing in a significant way. [ABSTRACT FROM AUTHOR]

The interaction of cold-vertically stratified (CVS) Mississippi River water with warm-horizontally stratified (WHS) Gulf of Mexico water resulted in a front that affected the oceanic surface layer. Our cross-frontal observations demonstrated two vertical layers. The cross-frontal deep layer (9–30 m) averaged a temperature dissipation rate (TD) varied by a factor of 1000 and was larger on the CVS side. The near-surface layer (0–9 m) averaged TD did not vary significantly across the front. The deep layer frontal asymmetry coincided with depths where the Thorpe scale was large. The situation was similar for the layer averaged turbulent kinetic energy dissipation rate (TKED). Within both layers, the averaged-TKED values were 10–30 times larger on the CVS side. The surface turbulent heat flux was up to 4 times larger on the WHS side. The observed asymmetric response of the turbulence across the front could play a significant role in the ocean-atmosphere climate system. [ABSTRACT FROM AUTHOR]

We have carried out an experimental study of the turbulence kinetic energy dissipation rate (ϵ), temperature dissipation rate (χ), and turbulent heat flux (THF) within the water surface layer in the presence of non-breaking wave, surface convection, and horizontal heat and eddy fluxes that play a prominent role in the front. We noted that the non-breaking wave dominates ϵ values within the surface layer. While analyzing the vertical ϵ variability, the presence of a wave-affected layer from the water surface to a depth of z ≈ 1.25 λ w is observed, where λ w is the wavelength. ϵ associated with non-breaking waves ranged to 4.9 × 10 − 6 – 7 × 10 − 6 m2/s3 for the wavelength range of 0.038 m < λ w < 0.098 m categorized as the gravity and gravity-capillary wave regimes. ϵ values increase for longer λ w and non-breaking wave ϵ values represent their significant contribution to the ocean energy budget and dynamic of surface layer considering that the non-breaking wave covers the large fraction of ocean surface. We also found that the surface mean square slope (MSS) and wave generated ϵ have the same order of magnitude, i.e., MSS ∼ ϵ . Besides, we have documented that the small-scale temperature fluctuation change (i.e., χ) is consistent with the large-scale temperature gradient change (i.e., d < T > / d z ). The value of the THF is approximately constant within the surface layer. It represents that the measured THF near the water surface can be considered a surface water THF, challenging to measure directly. [ABSTRACT FROM AUTHOR]