Field observations of turbulent dissipation rate profiles immediately below the air‐water interface

Wang, Binbin; Qian, Lei

doi:10.1002/2015jc011512

Cited by 19 publications

(16 citation statements)

References 45 publications

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“…Our observations support a depth dependency of ϵ described by b = −1.29 above z t , which is less than that proposed by T96 ( b = −2), which was supported by observations in Lake Michigan (Wang & Liao, ), in the Pacific Ocean at depths below approximately one H s (Sutherland & Melville, ), and in the laboratory (Siddiqui & Loewen, ) at depths below 0.4 H s . For measurements in coastal waters of the South China Sea, Shuiqing and Dongliang () find an even more gentle slope with b = −2.11.…”

Section: Discussionsupporting

confidence: 83%

“…The “breaking layer” would then be the depth at which half of the wind energy input has dissipated. Some studies find shallower depth levels for this “breaking depth,” e.g., z b = 0.4 H s (Jones & Monismith, ; Siddiqui & Loewen, ; Wang & Liao, ), z b = 0.25 H s (Young & Babanin, ) and z b = 0.01 H s (Thomson et al, , for a wave‐following reference frame). However, these studies observe ϵ closer to the surface than ϵ could be determined from ASIP measurements.…”

Section: Discussionmentioning

confidence: 99%

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Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

et al. 2018

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Direct observations of the dissipation rate of turbulent kinetic energy, ϵ, under open ocean conditions are limited. Consequently, our understanding of what chiefly controls dissipation in the open ocean, and its functional form with depth, is poorly constrained. In this study, we report direct open ocean measurements of ϵ from the Air‐Sea Interaction Profiler (ASIP) collected during five different cruises in the Atlantic Ocean. We then combine these data with ocean‐atmosphere flux measurements and wave information in order to evaluate existing turbulence scaling theories under a diverse set of open ocean conditions. Our results do not support the presence of a “breaking” or a “transition layer,” which has been previously suggested. Instead, ϵ decays as |z|−1.29 over the depth interval, which was previously defined as “transition layer,” and as |z|−1.15 over the mixing layer. This depth dependency does not significantly vary between nonbreaking or breaking wave conditions. A scaling relationship based on the friction velocity, the wave age, and the significant wave height describes the observations best for daytime conditions. For conditions during which convection is important, it is necessary to take buoyancy forcing into account.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

et al. 2018

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“…saline water), similar conditions of supercooling and turbulence are necessary for frazil ice production to begin. In polar regions, there are two common sets of conditions that produce different types of ice cover in the ocean (Weeks, 2010). The first is calm winds, cold air temperatures, and little swell and, in this case, frazil ice starts to form and freeze together into continuous skim ice on the sea surface.…”

Section: Introductionmentioning

confidence: 99%

“…The first is calm winds, cold air temperatures, and little swell and, in this case, frazil ice starts to form and freeze together into continuous skim ice on the sea surface. The second set of conditions that produce frazil ice are cold air temperatures with appreciable swell, waves, wind and blowing snow (Weeks, 2010). As ice production begins, frazil ice forms a slurry layer on the surface and as more ice is added to the layer, the viscosity of the layer continually increases.…”

Section: Introductionmentioning

confidence: 99%

Laboratory study of the properties of frazil ice particles and flocs in water of different salinities

2019

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Abstract. Measurements of the size and shape of frazil ice particles and flocs in saline water and of frazil ice flocs in freshwater are limited. This study consisted of a series of laboratory experiments producing frazil ice at salinities of 0 ‰, 15 ‰, 25 ‰ and 35 ‰ to address this lack of data. The experiments were conducted in a large tank in a cold room with bottom-mounted propellers to create turbulence. A high-resolution camera system was used to capture images of frazil ice particles and flocs passing through cross-polarizing lenses. The high-resolution images of the frazil ice were processed using a computer algorithm to differentiate particles from flocs and determine key properties including size, concentration and volume. The size and volume distributions of particles and flocs at all four salinities were found to fit log-normal distributions closely. The concentration, mean size, and standard deviation of flocs and particles were assessed at different times during the supercooling process to determine how these properties evolve with time. Comparisons were made to determine the effect of salinity on the properties of frazil ice particles and flocs. The overall mean size of frazil ice particles in saline water and freshwater was found to range between 0.52 and 0.45 mm, with particles sizes in freshwater ∼13 % larger than in saline water. However, qualitative observations showed that frazil ice particles in saline water tend to be more irregularly shaped. The overall mean size of flocs in freshwater was 2.57 mm compared to a mean size of 1.47 mm for flocs in saline water. The average growth rate of frazil particles was found to be 0.174, 0.070, 0.033, and 0.024 mm min−1 and the average floc growth rate was 0.408, 0.118, 0.089, and 0.072 mm min−1 for the 0 ‰, 15 ‰, 25 ‰, and 35 ‰, respectively. Estimates for the porosity of frazil ice flocs were made by equating the estimated volume of ice produced based on thermodynamic conditions to the estimated volume of ice determined from the digital images. The estimated porosities of frazil ice flocs were determined to be 0.86, 0.82, 0.8 and 0.75 for 0 ‰, 15 ‰, 25 ‰ and 35 ‰ saline water, respectively.

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“…This and further global quadratic relations feature a zero intercept [ Nightingale et al ., ; Sweeney et al ., ], which leads to the assumption of zero gas exchange at low wind speeds. It is known, however, that buoyancy effects, chemical enhancement, surface waves, and micro breaking events force gas exchange to occur even at low wind speeds [e.g., Sutherland and Melville , ; Wang and Liao , ]. McGillis et al .…”

Section: Introductionmentioning

confidence: 99%

Parameterizing air‐sea gas transfer velocity with dissipation

et al. 2017

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The air‐sea gas transfer velocity k is frequently estimated as an empirical function of wind speed. However, it is widely recognized that k depends on processes other than wind speed alone. The small‐eddy model, which describes periodic events of small eddies disturbing the sea surface with water from below, suggests a direct relation between k and the dissipation rate of turbulent kinetic energy ϵ at the air‐sea interface. This relation has been proven both in laboratories and in the field in various freshwater and coastal environments, but to date has not been verified in open ocean conditions. Here, concurrent North Atlantic field observations of ϵ and eddy covariance measurements of DMS and CO2 air‐sea gas flux are presented. Using ϵ measurements, we compare the small‐eddy model at various depths to previously published observations. Extrapolating the measured ϵ profiles to the thickness of the viscous sublayer allows us to formulate a function of k that depends solely on the water side friction velocity u∗w, which can be inferred from direct eddy covariance measurements of the air‐side friction velocity u∗a. These field observations are generally consistent with the theoretical small‐eddy model. Utilizing a variable Schmidt number exponent in the model, rather than a constant value of 12 yields improved agreement between model and observations.

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Field observations of turbulent dissipation rate profiles immediately below the air‐water interface

Cited by 19 publications

References 45 publications

Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

Laboratory study of the properties of frazil ice particles and flocs in water of different salinities

Parameterizing air‐sea gas transfer velocity with dissipation

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