Search

An adequate description of the interaction between the atmosphere and ocean remains one of the most important problems of modern oceanology and climatology. The extremely wide variety of physical processes occurring in the coupled layers, large range of scales, and moving boundary all significantly complicate the creation of models that would allow calculating the physical characteristics in both media with the necessary accuracy. In this paper the temporal variability of dynamic parameters in the driving layer of the atmosphere and in the near-surface layer of the sea on small and submesoscales from one to several tens of hours is considered. The experimental data show a very high correlation between the friction wind velocity and turbulence intensity in the upper sea layer on all scales recorded. One important distinguishing feature of all measured physical quantities in both media is the presence of quasi-periodic oscillations with different periods. For a more accurate description of momentum and energy fluxes from the atmosphere, a nonstationary model of turbulent exchange in the near-surface layer of the sea is proposed. It takes into account quasi-periodicity in the intensity of dynamic interaction between the atmosphere and the sea at these scales. In the model we use the equations of momentum and turbulent energy balance, the system of equations is solved numerically, and the calculation results are compared with other models and with experimental data. It is shown that taking into account the nonstationarity of the wind strain improves the correspondence between the calculations and the experimental data. It is noted that, in the nonstationary case, the energy and momentum flux from the atmosphere and the turbulence intensity increases compared to the action of a constant average wind of the same duration. Therefore, the strong averaging often used in global models may markedly underestimate the intensity of the dynamic interaction between the atmosphere and ocean. [ABSTRACT FROM AUTHOR]

We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (e) and of thermal/salinity/tracer variance (c), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable. [ABSTRACT FROM AUTHOR]

The coupling of three-level giant atoms with one-dimensional waveguides can show interesting phenomena of transmission and reflection. Since the non-waveguide mode can cause the dissipation of external atoms, we consider the effect of the dissipation rate on the scattering of single photons in the system with giant atom–waveguide coupling. We find that as the dissipation rate of giant atoms increases, the transmission rate of a single photon increases and the reflection rate decreases. In addition, by varying the phase difference and decay rate, the giant atoms are able to achieve perfect transmission and total reflection over the entire frequency range. We also find and show the conditions for the conversion of the optimal frequency. When the cumulative phase of photons reaches a certain value, the system can achieve perfect transmission, which is independent of frequency. This model of coupling giant atoms with waveguides has a promising application in quantum communication and quantum information processing. [ABSTRACT FROM AUTHOR]

We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (ϵ) and of thermal/salinity/tracer variance (χ), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable. [ABSTRACT FROM AUTHOR]

The eddy diffusivity in the ocean pycnocline K N = γ ε / N 2 is analyzed based on field measurements of the turbulent kinetic energy (TKE) dissipation rate ε z and buoyancy frequency N z profiles and an assumed mixing efficiency of γ = 0.2 . The microstructure measurements were taken between 2013 and 2019 in various regions of the Bay of Bengal (BoB) as well as the central Gulf Stream (GS) and deep waters of the Southern California Bight (SCB). The space–time variability of K N z , t observed in the pycnocline of the southeastern BoB is likely related to internal-wave generated turbulence, identified by its following of MacKinnon–Gregg scaling (MacKinnon and Gregg in J Phys Oceanogr 33(7):1476–1492, 2003). The probability distribution function of diffusivity CDF K N could be well fitted by generalized extreme value distribution (GEVD) for all regions of BoB and other oceans. Mixing rates in the upper pycnocline of BoB during extended southwestern monsoon period tend to be larger in the southern parts of the Bay compared to central and northern parts. Statistics of K N in the GS and SCB waters appear to be similar to those in the southern BoB with a characteristic median value ~ 2 × 10 - 6 m2/s, suggesting relatively low intensity of vertical mixing therein compared to the canonical pycnocline diffusivity of K N ≈ 10 - 5 m2/s. Article Highlights: Internal wave instabilities appear to be a dominant mechanism of generating energetic mixing events in the Bay of Bengal (BoB). Mixing rates (diffusivities) in the upper pycnocline tends to be larger in the southern BoB than in the northern part of the Bay. Generalized extreme value distribution approximates well the probability functions of the diffusivity in all tested regions of BoB as well as in the other oceans. [ABSTRACT FROM AUTHOR]

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10−10 to 4.18 × 10−7 W·kg−1. In the surface mixed layer, high values of ε (10−9∼10−8 W·kg−1) were observed toward the water surface. In the thermocline, ε was 10−9.5∼10−9 W·kg−1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations. [ABSTRACT FROM AUTHOR]

In the simulation of compressible turbulent flows via a high-order flux reconstruction framework, the artificial viscosity model plays an important role to ensure robustness in the strongly compressible region. However, the impact of the artificial viscosity model in under-resolved regions on dissipation features or resolving ability remains unclear. In this work, the performance of a dilation-based (DB) artificial viscosity model to simulate under-resolved turbulent flows in a high-order flux reconstruction (FR) framework is investigated. Comparison is conducted with results via several typical explicit subgrid scale (SGS) models as well as implicit large eddy simulation (iLES) and their impact on important diagnostic quantities including turbulent kinetic energy, total dissipation rate of kinetic energy, and energy spectra are discussed. The dissipation rate of kinetic energy is decomposed into several components including those resulting from explicit SGS models or Laplacian artificial viscosity model; thus, an explicit evaluation of the dissipation rate led by those modeling terms is presented. The test cases consist of the Taylor-Green vortex (TGV) problem at R e = 1600 , the freely decaying homogeneous isotropic turbulence (HIT) at M a t 0 = 0.5 (the initial turbulent Mach number), the compressible TGV at Mach number 1.25 and the compressible channel flow at R e b = 15,334 (the bulk Reynolds number based on bulk density, bulk velocity and half-height of the channel), Mach number 1.5. The first two cases show that the DB model behaves similarly to the SGS models in terms of dissipation and has the potential to improve the insufficient dissipation of iLES with the fourth-order-accurate FR method. The last two cases further demonstrate the ability of the DB method on compresssible under-resolved turbulence and/or wall-bounded turbulence. The results of this work suggest the general suitability of the DB model to simulate under-resolved compressible turbulence in the high order flux reconstruction framework and also suggest some future work on controlling the potential excessive dissipation caused by the dilation term. [ABSTRACT FROM AUTHOR]

Nonstationary convection forced by distributed buoyancy sources is a fundamental environmental fluid mechanics process, particularly in ice-covered freshwater waterbodies. In this paper, we present novel field-based results that characterise the diurnal evolution of the main energetics of radiatively-driven convection in ice-covered lakes that is the radiatively-induced buoyancy flux, B, and the kinetic energy dissipation rate, ε . To estimate the spatiotemporal distribution of ε , we applied scale similarity of the velocity structure functions to identify the fine turbulence scales from high-frequency velocity measurements. The field study was carried out at Lake Vendyurskoe, Russia, in April 2016. Small-scale velocity fluctuations were measured using acoustic Doppler current profiler in a 2 m layer beneath the ice cover. The method was proven to be valid for low-energy convection without mean shear. The inertial subrange, covering order of magnitude in the spatial domain, was identified by fitting the 2 / 3 scaling power law to the structure function method, thus confirming the regime of fully developed turbulence. The calculated rate of dissipation of turbulent kinetic energy ε reaches values up to 3 × 10 - 9 m 2 s - 3 . Although a strong correlation between ε and B was observed, ε picks up about 1 h later after the onset of the heating-phase. This delay roughly corresponds to the turnover time of the energy containing eddies. We finally observed a decay of ε at night, during the relaxation-phase, but, interestingly, the level remained above the statistical error. [ABSTRACT FROM AUTHOR]

A system of edge cracks was applied to polished (010) surfaces of K-rich gem-quality alkali feldspar by diffusion-mediated cation exchange between oriented feldspar plates and a Na-rich NaCl–KCl salt melt. The cation exchange produced a Na-rich layer at and beneath the specimen surface, and the associated strongly anisotropic lattice contraction lead to a tensile stress state at the specimen surface, which induced fracturing. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth. The cracks nucleated with non-uniform spacing on the sample surface and quickly attained nearly uniform spacing below the surface by systematic turning along their early propagation paths. In places, conspicuous wavy cracks oscillating several times before attaining their final position between the neighboring cracks were produced. It is shown that the evolution of irregularly spaced towards regularly spaced cracks including the systematic turning and wavyness along the early propagation paths maximizes the rate of free energy dissipation in every evolutionary stage of the system. Maximization of the dissipation rate is suggested as a criterion for selection of the most probable evolution path for a system undergoing chemically induced diffusion mediated fracturing in an anisotropic homogeneous brittle material. [ABSTRACT FROM AUTHOR]

The global diapycnal transport in the ocean interior is one of the significant branches to return the deep water back toward near-surface. However, the amount of the diapycnal transport and the seasonal variations are not determined yet. This paper estimates the dissipation rate and the associated diapycnal transports at 500 m, 750 m and 1 000 m depth throughout the global ocean from the wide-spread Argo profiles, using the finescale parameterizations and classic advection-diffusion balance. The net upwelling is ~5.2±0.81 Sv (Sverdrup) which is approximately one fifth in magnitude of the formation of the deep water. The Southern Ocean is the major region with the upward diapycnal transport, while the downwelling emerges mainly in the northern North Atlantic. The upwelling in the Southern Ocean accounts for over 50% of the amount of the global summation. The seasonal cycle is obvious at 500 m and vanishes with depth, indicating the energy source at surface. The enhancement of diapycnal transport occurs at 1 000 m in the Southern Ocean, which is pertinent with the internal wave generation due to the interaction between the robust deep-reaching flows and the rough topography. Our estimates of the diapycnal transport in the ocean interior have implications for the closure of the oceanic energy budget and the understanding of global Meridional Overturning Circulation. [ABSTRACT FROM AUTHOR]

The present paper uses Langevin dynamics (LD) to investigate the aggregation of soot nano-particles in turbulent flows. Interparticle forces are included, and the computation of the individual particles by LD is retained even after aggregate formation such that collision events and locations can be based on center-to-center particle distances without invoking any modelling assumptions of aggregate shape and/or collision frequency. We focus on the interactions between the specific hydrodynamic conditions and the particle properties and their effect on the resulting agglomerates' morphologies. The morphology is characterized by the fractal dimension, D . Computations of particle aggregation in homogeneous isotropic turbulence and in shear flows dominated by counter-rotating vortices with a wide range of turbulence intensities and particle sizes indicate that the evolution of the agglomerates' shapes can be adequately parameterized by the size of the agglomerates and the Knudsen and Péclet numbers, the latter being based on the smallest turbulence scales. The computations further suggest that the shapes of agglomerates of certain sizes are relatively independent of time and relatively insensitive to larger turbulence structures. The fractal dimensions are modelled as functions of radius of gyration, Kn and Pe. The fitted expressions show good agreement with the LD simulations and represent the entire growth process of the agglomerates. A direct comparison of selected aggregates with experimental data shows very good qualitative agreement. A thorough quantitative validation of the evolution of the computed aggregate characteristics is, however, presently hindered by the challenges for and therefore lack of suitable experiments under appropriately controlled conditions. [ABSTRACT FROM AUTHOR]

Soft marine deposits are widely distributed in the coastal region of China. The marine soft clays have high water content and high sensitivity, which shows high compressibility and low strength. The installation of precast piles for wind turbines over soft marine clay will generate high excess pore water pressure (EPWP) with very low dissipation rate, resulting in low bearing capacity and large postconstruction settlement, which will affect long-term stability. This study investigated the generation and dissipation of the EPWP correlated with the change in soil structure during the installation of pile foundations in a project of 100 MW wind-power generation in Lianyungang, Jiangsu, China. The results show that the marine soft clay soils feature strong natural structures based on the intrinsic compression concept. The EPWP decreases with increasing distance from the pile, whose influence reaches a distance of 6 m (about 10 times the pile side length). The structural strength of natural sedimentary clay has a remarkable impact on the generated EPWP. The dissipation rate of the EPWP is very slow in mucky clay with more than half the residual value after 30 days, which is mainly attributed to the sharp decline of consolidation coefficient induced by the disturbance of natural clay soils from pile driving. Moreover, hydraulic fracturing can well explain the dissipation characteristics of the EPWP in clay. This phenomenon is actually an ongoing process especially in marine soft clay soils with a strong cementation effect. [ABSTRACT FROM AUTHOR]

The upper boundary layer of the sea is most affected by the atmosphere, and the motions formed there have a significant influence on the horizontal and vertical fluxes of heat, momentum, and other substances. The vertical turbulent exchange in this layer is determined by the action of several mechanisms at once, one of which is the surface wave. Estimates of the contribution of a wave to the overall generation of turbulence have been made by many researchers using a variety of approaches. To verify the proposed turbulence generation models, experimental data on the intensity of turbulent velocity fluctuations in the near-surface sea layer obtained on an oceanographic platform are used. The turbulent energy dissipation rate is calculated using the vertical component of velocity vector fluctuations using the Kolmogorov hypothesis and Taylor's frozen turbulence hypothesis. A comparison of model and experimental data of dissipation rate values show the validity of the basic assumption that the intensity of wave-induced turbulence depends on the energy characteristics of the wave. At the same time, in situ data decrease with depth much slower than calculated data. A possible explanation could be the influence of turbulent diffusion and shear effects, as well as the inadequate parameterization of the wave energy transformation into turbulence. [ABSTRACT FROM AUTHOR]

In this paper, a Reynolds number increase transition from self-oscillations close to single-frequency ones to the temporally chaotic regime in the flow in a cylindrical channel driven by a spatially periodic force with four half-periods is experimentally investigated. The parameter ε proportional to the mean rate of the kinetic energy dissipation in unit mass per unit time associated with perturbations in the fluid is used as a basic characteristic of self-oscillations. The Reynolds number dependence ε(Re) for single frequency self-oscillations is considered theoretically. [ABSTRACT FROM AUTHOR]

The vertical structure of internal tide dissipation rate ϵ is essential to the parameterization of the internal tide‐induced mixing, yet its diversity has always been oversimplified in ocean circulation models. Based on a high‐vertical‐resolution (10 m) simulation around the exits of the Indonesian throughflow, the diversity in ϵ profiles near both the bottom and the thermocline was investigated by a hierarchical clustering classification. Five typical near‐bottom vertical structures of ϵ were found, of which the bottom‐intensified structure is dominant. From the maximum dissipation depths to the shallower water, all five profiles obey the same decaying function. There are three typical near‐thermocline structures of ϵ: one menifests the thermocline‐intensified pattern and the other two feature a surface‐intensified pattern characterized by a monotonic increase from 500‐m depth to the surface. All three vertical structures near thermocline could be scaled by the reciprocal of the Richardson number. Plain Language Summary: Tidal currents flow over the uneven seafloor back and forth every day, causing mixing between adjacent vertical layers in the ocean. This process, known as tidal mixing, occurs in the whole ocean and is strong around the exits of the Indonesian throughflow (ITF). The vertical distribution of the tidal mixing is one of the primary elements that shapes the profiles of temperature and salinity and modulates the transports in the Indonesian seas. Previous studies suggested that tidal mixing is intensified at the bottom and the thermocline without considering its diversity in the real ocean. The diversity in the profiles of the tidal mixing around the exits of the ITF is explored. We found that, adjacent to the bottom topography, the mixing is intensified not only at the bottom but also at depths of hundreds of meters above the bottom and all of profiles obey the same decaying law from the maximum mixing depths to the shallower water. Near the thermocline, the tidal mixing is thermocline‐intensified away from the archipelago and surface‐intensified near the archipelago. These findings shed light on the vertical structures of tidal mixing in the ocean and are potentially valuable to improve the performance of ocean circulation models. Key Points: Diversity in the profiles of tide‐induced dissipation rate around the exits of the Indonesian throughflow is investigatedFive typical profiles are revealed near the bottom, obeying the same decaying law from the maximum dissipation depths to shallower waterThree typical profiles near the thermocline are also revealed, all of which can be scaled with the reciprocal of the Richardson number [ABSTRACT FROM AUTHOR]

From April 24 to October 25, 2011, an Acoustic Doppler Velocimeter (ADV) continually running for 185 d was mounted on the smooth ridge at the edge of Monterey Canyon to observe turbulence in the bottom boundary layer. The ADV was set at 1.4 m above the bed bottom, continuously run for 1 min with a 2-minute interval with sampling frequency 64 Hz. The long-time continual observation is significant to reveal variations of turbulent characteristics and show some differences from the classic traditional turbulent theory. Eliminating the noise by the 'Phase-Space Thresholding Method', rotating the coordinate and low-pass filtering the velocity were applied for data processing. This paper was mainly to estimate the turbulent kinetic energy dissipation rate by the inertial dissipation method, friction velocity, drag coefficient and significant periods of the turbulent characteristics with the ADV data. The results show that there is a strong, rotating bottom flow up to 0.398 m s with predominantly semidiurnal period and less significantly diurnal and semilunar period. The turbulent kinetic energy dissipation rate ranges from 1.09×10 W kg to 6.62×10 W kg, which can vary with 2 or 3 orders of magnitude in one day. The daily averaged variations of friction velocity and drag coefficient are 6.50×10-2.32×10 m s and 6.30×10-4.36×10, respectively. All the characteristics have a remarkable semidiurnal period. In the bottom boundary layer with a rotating tide, the parameterized coefficients to describe ɛ- u* and ɛ- E relationships are much smaller than the traditional value. [ABSTRACT FROM AUTHOR]

In the Arctic Ocean, limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong. However, mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to Arctic Ocean state are poorly understood. We present measurements from the shelf north of Svalbard that show abrupt isopycnal vertical displacements of 10–50 m and intense dissipation associated with cross‐isobath diurnal tidal currents of ∼0.15 m s−1. Energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water. During a 6‐hr turbulent event, high‐frequency internal waves were present, the full 300‐m depth water column became turbulent, dissipation rates increased by a factor of 100, and turbulent heat flux averaged 15 W m−2 compared with the background rate of 1 W m−2. Plain Language Summary: Turbulent mixing in the Arctic Ocean water column affects sea ice variability through transport of subsurface heat toward the surface. This turbulent mixing is concentrated along the margins, mainly driven by tidal flow over sloping topography. However, processes of energy transfer from tides to turbulence in the Arctic are poorly understood, and the magnitudes and locations of mixing are poorly constrained. Here we present detailed measurements from the shelf north of Svalbard, showing a turbulent event driven by moderate tidal currents. The energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent. Our observations imply that this process is an important source of mixing in the Arctic Ocean. Key Points: Cross‐isobath diurnal currents generate nonlinear internal waves north of SvalbardFlow becomes supercritical during maximum off‐shelf tidal flowTime‐averaged turbulent heat fluxes increase by a factor of 4 when the turbulent period is included [ABSTRACT FROM AUTHOR]

Accurate estimation of dissipation rate is important in understanding and analyzing turbulent flows found in environment and engineering processes. Many previous studies have focused on measuring the local dissipation rate at a single point or averaged dissipation rate over a suitable area. Since coherent Doppler lidar is capable of providing multi-point measurements covering a large spatial extent, it is well-suited for examining the distribution of dissipation in the atmosphere. In this paper, an approach is presented that is based on retrieving the dissipation rate from coherent Doppler lidar data using large-eddy simulation. Two Coherent Doppler lidars performed range height indicator (RHI) scans of a vertical/cross-barrier plane during the Terrain-induced Rotor Experiment (T-REX). Two-dimensional velocity vectors were retrieved using a least squares method. The velocity vectors retrieved from co-planar RHI scans are used to estimate subgrid scale (SGS) quantities through a known SGS parameterization. For the T-REX datasets analyzed, the dissipation rate was found to increase in the presence of rotors, subrotors, and, as expected, in regions of high wind shear. Owing to the presence of sharper gradients in subrotors, their dissipation rate is generally larger than that of rotors. [ABSTRACT FROM AUTHOR]

The adsorption process is a highly efficient and widely applied fundamental technique in the field of Geo-environmental engineering. Most existing adsorption models are empirical or semi-empirical and lack a consistent and unified scientific theoretical basis. In this work, a new adsorption kinetic model with dispersion-type (D-type) has been proposed within the framework of irreversible thermodynamics for investigating the adsorption behavior of a single ionic species onto a solid adsorbent. Based on Ziegler's maximal rate of dissipation, an expression for mass exchange rate was determined after a detailed theoretical deviation by defining the thermodynamic force and thermodynamic flow; and by formulating two dispersion-type free energy functions and a dispersion-type dissipation rate density function. The mass exchange rate expression was introduced into the mass balance equation as further validation of the D-type adsorption kinetic model for a single system. Comparing the adsorption process predicted by the presented model with the tested adsorption processes of Pb2+ and Cd2+ onto beidellite and Pb2+ on bentonite, the results reveal good agreement with experimental data. The D-type adsorption kinetic model could provide a correct description of the kinetics of adsorption process for single ionic species onto solid adsorbent. [ABSTRACT FROM AUTHOR]

The study of heat transfer on shear flows around an obstacle presents a great interest in determination of the influence of water on buildings and port infrastructures. The variation of the inlet temperatures and the influence of an obstacle placed at the bottom of a channel were analyzed. The obtained results supported by numerical simulations have shown that the doubling of the fluid inlet temperature significantly modifies all the dynamic characteristics of the shear flow. Pressure distribution, turbulent kinetic energy, dissipation rate, turbulent viscosity, and strain rate in the water channel were exposed. These results can help us to better exploit the flow of hot water discharged by power plants. [ABSTRACT FROM AUTHOR]

Discontinuity of the dissipation rate associated with the temperature variance at the fluid-solid interface is analyzed in a turbulent channel flow at a Reynolds number, based on the friction velocity of 395 and a Prandtl number of 0.71. The analysis is performed with a wall-resolved Large Eddy Simulation and the results are used to derive a regression for the dissipation rate discontinuity, which depends only on the fluid-solid thermal diffusivity and conductivity ratios. Wall-resolved Large Eddy Simulations at a higher Reynolds number and a higher Prandtl number are used to investigate the validity of two correlations derived from the regression for the selected thermal properties ratios. The present results are obtained with the open-source Computational Fluid Dynamics solver Code_Saturne, and use the fully conservative fluid-solid thermal coupling capability introduced by the authors in version 5.0. [ABSTRACT FROM AUTHOR]

This paper focuses on the impact of an oscillating low-speed current on the structure and dynamics of the bottom-boundary layer (BBL) in a small stratified basin. A set of high-resolution current profile measurements in combination with temperature-microstructure measurements were collected during a complete cycle of the internal oscillation (`seiching') in the BBL of Lake Alpnach, Switzerland. It was found that even a relatively long seiching period of 24 hours significantly changed the form of the near-bottom current profiles as well as the dynamics of the turbulent dissipation rate compared to the steady-state law-of-the-wall. A logarithmic fit to the measured current profiles starting at a distance of 0.5 m above the sediment led to inconsistent estimates of both friction velocity and roughness length. Moreover, a phase lag between the current and the turbulent dissipation of 1.5 hours and a persistent maximum in the current profile at a height of 2.5 to 3 m above the sediment were observed. The experimental findings were compared to the results of a k-ε turbulence model and showed good agreement in general. Specifically, the inconsistent logarithmic fitting results and the observed phase lag were reproduced well by the model. [ABSTRACT FROM AUTHOR]

The probability distribution of turbulent kinetic energy dissipation rate in stratified ocean usually deviates from the classic lognormal distribution that has been formulated for and often observed in unstratified homogeneous layers of atmospheric and oceanic turbulence. Our measurements of vertical profiles of micro-scale shear, collected in the East China Sea, northern Bay of Bengal, to the south and east of Sri Lanka, and in the Gulf Stream region, show that the probability distributions of the dissipation rate [ABSTRACT FROM AUTHOR]

Measurements of the turbulent kinetic energy dissipation rate ( ε), velocity, temperature, and salinity were obtained for the upper ocean of the central South China Sea (14.5° N, 117.0° E) during an experimental campaign from May 11 to 13, 2010. Dissipation in the diurnal mixed layer showed a diurnal variability that was strongly affected by the surface buoyancy flux. Dissipation was enhanced ( ε ∼ 10 W kg) at night due to the convective mixing and was weakened ( ε ∼ 10 W kg) in daytime due to the stratification. Dissipation in the thermocline varied with time under the influence of internal waves. Shear from high-frequency internal waves (period ∼8 h) played an important role in enhancing the turbulent mixing in the thermocline. In the period of strong high-frequency internal waves, the shear from high-frequency internal waves became strong and the depth-averaged ε in the thermocline was elevated by almost one order of magnitude. Compared with the dissipation in the thermocline, dissipation below was weaker (the time-averaged ε ∼ 10 W kg). The observation indicates that the dissipation rates during the measurements can be parameterized by the MacKinnon-Gregg model that is widely used in the continental shelf but are not in agreement with the Gregg-Henyey model used for the open ocean. [ABSTRACT FROM AUTHOR]

The friction velocity (u*) and the sensible heat flux density (H) determined with a displaced-beam small aperture scintillometer (DBSAS) and a hot-film eddy correlation system are compared. Random errors in the DBSAS are relatively small, compared to scatter found with two eddy-correlation systems. Assuming that the hot-film system yields the `true' fluxes, the DBSAS appears to overestimate u* when u* is less than ≈0.2 m s-1 and to underestimate u* at high wind speeds. This implies that the DBSAS measurements of the inner scale length of turbulence, l0, a direct measure for the dissipation rate of kinetic turbulent energy, are biased. Possible causes for these results are discussed in detail. A correction procedure is presented to account for effects of random noise and of so-called inactive turbulence or sensor vibrations. The errors in u* cause errors in the DBSAS measurements of the structure parameter of temperature CT2. The derived H appears to be less sensitive to errors in l0 and CT2, because errors in these quantities tend to cancel out. [ABSTRACT FROM AUTHOR]

Measurements for long-term ocean turbulence observation are obtained from a mooring line deployed in the South China Sea. The measurements were made at a single level of 250-m depth in the water column for about three-month duty cycle. We concentrate on the shear velocity measurements and processing. The correlation between the vibration noise and the motion of the platform is analyzed. A multivariate correction procedure is applied to remove vehicle motion and vibration contamination from the estimates of the turbulent kinetic energy (TKE) terms. These time-extended measurements of TKE have yielded a valuable database. Based on advanced spectral methods, the evolution processes of ocean turbulence in the South China Sea are illustrated by the dissipation time series. The distribution patterns of dissipation in different time scales reveal the multiscale evolution and time dependence over the tidal cycle. The extended observations of dissipation will contribute to improving our understanding of the ocean evolution processes in the South China Sea. [ABSTRACT FROM AUTHOR]

Chlorothalonil and azoxystrobin, as efficient and broad-spectrum fungicides, are two widely used fungicides to control downy mildew and anthracnose on cabbage. For the safe and rational use of these two pesticides on cabbage, their residues and dissipation were studied under field conditions. The trial results showed that chlorothalonil and azoxystrobin residues were affected by the frequency and dosage of application, and the weather condition post-application. Chlorothalonil and azoxystrobin dissipated rapidly in cabbage with the mean half-live of 1.7 and 0.4 days at three geographical experimental plots in China, respectively. The terminal residues of chlorothalonil and azoxystrobin in cabbage at harvest time were all below the maximum residue limit (MRL, 6 mg kg−1for chlorothalonil and 5 mg kg−1for azoxystrobin) established by Codex Alimentarius Commission. It suggested that this formulation of chlorothalonil and azoxystrobin (560 g L−1, SC) may be safer under the recommended dosage. Given that in China no MRL has been set for chlorothalonil and azoxystrobin in cabbage, this study could provide a guidance for establishing MRL, and the safe and rational use of these two pesticides. [ABSTRACT FROM PUBLISHER]

Estimation of the turbulent dissipation rate in a boundary layer is a very involved process. Experimental determination of either the dissipation rate or the Taylor microscale, even in isotropic turbulence, which may occur in a portion of the turbulent boundary layer, is known to be a difficult task. For constant pressure boundary layers, a model for the turbulent dissipation rate is proposed here in terms of the local mean flow quantities. Comparable agreement between the estimated Taylor microscale and Kolmogorov length scale with other data in the logarithmic region suggests usefulness of this model in obtaining these quantities experimentally. [ABSTRACT FROM AUTHOR]

Turbulent mixing in the upper ocean (30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature, salinity and microstructure data obtained during February 2014. Vertical thermohaline structures are distinct due to geographic features and sea ice distribution, resulting in that turbulent dissipation rates ( ε) and turbulent diffusivity ( K) are vertically and spatially non-uniform. On the shelf north of Antarctic Peninsula and Philip Ridge, with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m, both ε and K show significantly enhanced values in the order of O(10)- O(10) W/kg and O(10)- O(10) m/s respectively, about two or three orders of magnitude higher than those in the open ocean. Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau, where ε decreases with depth from O(10) to O(10) W/kg, while K changes vertically in an inverse direction relative to ε from O(10) to O(10) m/s. In the marginal ice zone, K is vertically stable with the order of 10 m/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer. Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions, our results indicate weak relationship between K and wind stress or tidal kinetic energy. Instead, intensified mixing occurs with large bottom roughness, demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing. In addition, geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing. [ABSTRACT FROM AUTHOR]

A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order of magnitude larger than that in the open ocean at that low latitude. Enhanced eddy diffusivities by strong shears and sharp changes in topography were observed. The strongest eddy diffusivity occurred in the mixed layer, and it reached O(10 m/s). Strong stratification in the thermocline inhibited the penetration of surface eddy diffusivities through the thermocline, where the mixing was weakest. Below the thermocline, where the background eddy diffusivity was approximately O(10 m/s), the eddy diffusivity increased with depth, and its largest value was O(10 m/s). [ABSTRACT FROM AUTHOR]

A new moored microstructure recorder (MMR) is designed, developed, tested, and evaluated. The MMR directly measures the high-frequency shear of velocity fluctuations, with which we can estimate the dissipation rate of turbulent kinetic energy. We summarize and discuss methods for estimating the turbulent kinetic energy dissipation rate. Instrument body vibrations contaminate the shear signal in an ocean field experiment, and a compensating correction successfully removes this contamination. In both tank test and ocean field experiment, the dissipation rate measured with the MMR agreed well with that measured using other instruments. [ABSTRACT FROM AUTHOR]

Structure functions of sound speed and local entropy in the turbulent atmosphere are analyzed. By long-term measurements in the atmospheric boundary layer the power dependence of these characteristics in the inertial sub-range is significantly diverged from the '2/3 law'. Behavior of structure functions indicates deviation from the asymptotic Kolmogorov-Obukhov law on scales, which significantly exceed Taylor microscale. The exponent of 2/3 is regarded as the limit value, which can be reached under different synoptic conditions. Analytical expressions for the internal and 'energy' scales of entropy fluctuations, as well as for relation of these scales with entropy dissipation rate and energy of adiabatic fluctuations are proposed. [ABSTRACT FROM AUTHOR]

The along-coast, offshore turbulence structure of the Bora flow that occurred on 7 November 1999 during the Mesoscale Alpine Programme (MAP) Intensive Observation Period 15 is examined. In this analysis we employ the aircraft and dropsonde data obtained over the Adriatic Sea, where the turbulence structure is determined by estimating turbulent kinetic energy (TKE) and its dissipation rate along the flight legs. The turbulence characteristics of Bora in the lee of the Dinaric Alps is greatly influenced by the mesoscale Bora flow structure over the Adriatic Sea, which in the cross-wind direction features an interchange of jets and wakes related to mountain gaps and peaks. In order to establish the origin of turbulence, the Weather Research and Forecasting-Advanced Research WRF (WRF-ARW) numerical model is used and its results are compared to the measurements. All five TKE-prediction parametrization schemes available in the model show reasonable agreement with the measured values. Since these parametrization schemes do not have horizontal advection included, they suggest that the along-flight structure of the Bora turbulence is principally generated by the local vertical wind shear. Further evidence is needed to support this hypothesis. [ABSTRACT FROM AUTHOR]

Tethered Lifting System (TLS) estimates of the dissipation rate of turbulent kinetic energy $${(\varepsilon)}$$ are reasonably well correlated with concurrent measurements of vertical velocity variance $${(\sigma_{w}^{2})}$$ obtained from sonic anemometers located on a nearby 60-m tower during the CASES-99 field experiment. Additional results in the first 100 m of the nocturnal stable boundary layer confirm our earlier claim that the presence of weak but persistent background turbulence exists even during the most stable atmospheric conditions, where $${\varepsilon}$$ can exhibit values as low as 10 m s. We also present a set of empirical equations that incorporates TLS measurements of temperature, horizontal wind speed, and $${\varepsilon}$$ to provide a proxy measurement for $${\sigma_{w}^{2}}$$ at altitudes higher than tower heights. [ABSTRACT FROM AUTHOR]

The energy dissipation rate is an important concept in the theory of turbulence. Doering-Constantin’s variational principle characterizes the upper bounds (maximum) of the time-averaged rate of viscous energy dissipation. In the present study, an optimization theoretical point of view was adopted to recast Doering-Constantin’s formulation into a minimax principle for the energy dissipation of an incompressible shear flow. Then, the Kakutani minimax theorem in the game theory is applied to obtain a set of conditions, under which the maximization and the minimization in the minimax principle are commutative. The results explain the spectral constraint of Doering-Constantin, and confirm the equivalence between Doering-Constantin’s variational principle and Howard-Busse’s statistical turbulence theory. [ABSTRACT FROM AUTHOR]

Experimental investigations have been devoted to the study of scaling law of coarse-grained dissipation rate structure function for velocity and temperature fluctuation of non-isotropic and inhomogeneous turbulent flows at moderate Reynolds number. Much attention has been paid to the case of turbulent boundary layer, which is typically the nonistropic and inhomogeneous trubulence because of the dynamically important existence of organized coherent structure burst process in the near wall region. Longitudinal velocity and temperature have been measured at different vertical positions in turbulent boundary layer over a heated and unheated flat plate in a wind tunnel using hot wire anemometer. The influence of non-isotropy and inhomogeneity and heating the wall on the scaling law of the dissipation rate structure function is studied because of the existence of organized coherent structure burst process in the near wall region. The scaling law of coarse-grained dissipation rate structure function is found to be independent of the mean velocity shear strain and the heating wall boundary condition. The scaling law of the dissipation rate structure function is verified to be in agreement with the hierarchical structure model that has been verified valid for isotropic and homogeneous turbulence. [ABSTRACT FROM AUTHOR]

We prove spatial analyticity for solutions of the stochastically forced Navier–Stokes equation, provided that the forcing is sufficiently smooth spatially. We also give estimates, which extend to the stationary regime, providing strong control of both of the expected rate of dissipation and fluctuations about this mean. Surprisingly, we could not obtain non-random estimates of the exponential decay rate of the spatial Fourier spectra. [ABSTRACT FROM AUTHOR]

The study is focused on the retrieval and validation of the turbulent kinetic energy dissipation rate ℇfrom spectral width measurements made by a UHF wind profiler in the convective atmospheric boundary layer. The possibility to deduce ℇ, which is one of the most important parameters for boundary-layer study and monitoring, from Doppler radar spectral width measurements has a firm theoretical basis established by numerous earlier works. However, the major drawback of this approach lies in various meteorological and instrumental sources of non-turbulent spectral width broadening which have to be recognised and accounted for. In the first part of the study, the theoretical background of the ℇ retrieval is detailed and all possible causes of spectral broadening are listed and evaluated. In the second part, the method is applied to four days of UHF diurnal boundary-layer observations, collected during the TRAC-98 experiment, for which in situ aircraft ℇ measurements were available. Comparison between radar-retrieved ℇand in situ aircraft measurements yields a fairly good agreement with a linear correlation coefficient of about 0.9 and a residual bias less than 2 × 10-4 m2 s-3. The analysis of ℇderived from vertical and off-zenith observation leads to the recommendation, that in the boundary layer, where the wind is usually moderate, data collected by off-zenith beams should be used. Indeed, the measurement of the vertical spectral width, less affected by the large-scale broadening factor, can still be altered by the ground clutter removal. [ABSTRACT FROM AUTHOR]

Micrometeorological data for wind and temperature from a 325 m high lower in Beijing City are analyzed by use of local similarty theory Non–dimentional wind and temperature gradients Φ and Φ are determined by three techniques called respectively, eddy-correlation, mean profiles and inertia subrange cospectra (ISC) method for a wide range of atmospheric stratification from unstable to stable condition Average dissipation rate Φof turbulent kinetic energy (TKE) is evaluated from u-spectrum as a quanlity required in the last technique. Ratio of the eddy transfer coefficients. α(= K / K) is calculated from Φ and Φ estimations. The results from various techniques are compared with each other and with some available empirical results in the lwor -layer. it is shown that the empirical relationship detefrmined by mean profiles and ISC methods in the lower-layer turbulence are in agreement with each other and with some other results. [ABSTRACT FROM AUTHOR]

A 3-D wave model for the turbulent coherent structures in near-wall region is proposed. The transport nature of the Reynolds stresses and dissipation rate of the turbulence kinetic energy are shown via computation based on the theoretical model. The mean velocity profile is also computed by using the same theoretical model. The theoretical results are in good agreement with those found from DNS, indicating that the theoretical model proposed can correctly describe the physical mechanism of turbulence in near wall region and it thus possibly opens a new way for turbulence modeling in this region. [ABSTRACT FROM AUTHOR]

The MST (Microstructure-Turbulence) Profiler is a newly developed operational microstructure measuring system, specially designed for marine and limnic turbulence measurements. The profiler can be used for sinking and uprising measurements and is equipped with a new type of current shear sensor. We have tested the MST Profiler in several field measuring campaigns in deep Alpine lakes. The investigations were focused on the internal vibration level of the profiler and its lower detection limit for dissipation rate estimates (pseudo dissipation). The upper detection limit was estimated based on the geometry of the shear sensor. The test measurements gave no indication of pronounced internal profiler vibrations interfering with dissipation measurements. The pseudo dissipation level (noise) of the profiler was found to be as low as 5 ˙ 10-12W/kg under quiet conditions at sinking velocities below 0.4m/s. At 0.8m/s sinking velocity, a pseudo dissipation of 4 ˙ 10-11W/kg was obtained. At rising measurements with additional sources of profiler vibrations due to influence of the cable the pseudo dissipation is about twice that for sinking measurements. For the upper detection limit which can be measured without correction for unresolved variance of the shear spectrum, a value of 10-4 W/kg was estimated. [ABSTRACT FROM AUTHOR]

It has been recognized that the turbulent cross helicity (correlation between the velocity and magnetic-field fluctuations) can play an important role in several magnetohydrodynamic plasma phenomena such as the global magnetic-field generation, turbulence suppression, and so on. Despite its relevance to the cross-helicity evolution, little attention has been paid to the dissipation rate of the turbulent cross helicity, εW. In this paper, we consider the model expression for εW. In addition to the algebraic model, an evolution equation of εW is proposed on the basis of the statistical analytical theory of inhomogeneous turbulence. A turbulence model with the modeling of εW is applied to the solar-wind turbulence. Numerical results on the large-scale evolution of cross helicity are compared with the satellite observations. It is shown that, as far as the solar-wind application is concerned, the simplest possible algebraic model for εW is sufficient for elucidating the large-scale spatial evolution of the solar-wind turbulence. Dependence of the cross-helicity evolution on the large-scale velocity structures, such as velocity shear and flow expansion, is also discussed. [ABSTRACT FROM AUTHOR]

The kinetic energy of turbulence, the dissipation rate of turbulent energy, and the integral scale of turbulence in the stable atmospheric boundary layer at the location heights of low-level jets (LLJs) have been measured with a coherent Doppler light detection and ranging (lidar) system. The turbulence is shown to be weak in the central part of LLJs. The kinetic energy of turbulence at the maximum velocity heights of the jet does not exceed 0.1 (m/s)2, while the dissipation rate is about 10−5 m2/s3. On average, the integral scale of turbulence in the central part of the jet is about 100 m, which is two to three times less than the effective vertical size of the LLJ. [ABSTRACT FROM AUTHOR]