Search

Purpose. The purpose of the study is to assess the coefficient of vertical turbulent exchange for different layers of the Black Sea basin based on the experimental data on microstructure of the physical fields obtained for the period 2004–2019 in the Black Sea and using the semi-empirical models. Methods and Results. For the upper mixed layer, the turbulent energy dissipation rate ɛ and the exchange coefficient were calculated using the velocity fluctuation spectra based on the Kolmogorov hypotheses on the turbulence spectrum inertial range. In the stratified layers, the turbulence coefficient and the dissipation rate were experimentally determined both from the spectra of the velocity horizontal fluctuations’ gradients and the vertical spectra of temperature fluctuations using the concept of the effective scale of turbulent patches. Depending on the features of the hydrological regime and the prevailing energy contributors to turbulence generation, five layers were identified and described (including their characteristic power dependences of the vertical turbulent diffusion coefficients K on the buoyancy frequency N) using the 1.5D-model of vertical turbulent exchange for the basin under study. For the stratified layers, the 1.5D-model results were comparatively analyzed with those of the other semi-empirical and theoretical models describing the most probable hydrophysical processes in each specific layer; the relations for the vertical turbulent exchange coefficient were obtained depending on the buoyancy frequency. Conclusions. Comparison of the experimental data collected under different hydrometeorological conditions with the simulations resulted from the known turbulence models for the sea upper layer showed that the best agreement between the simulation and measurement data was provided by a multiscale model taking into account three basic mechanisms of turbulence generation: current velocity shear, instability of wave motions, and wave breaking. The turbulent exchange coefficient dependencies on depth are conditioned by the effect of the turbulence dominant source at a given level. In the stratified layers, the exchange coefficient dependence on buoyancy frequency is determined by the hydrophysical processes in each layer; the relations obtained for individual layers indicate intensity of the contributions of vertical advection, internal wave breakings, turbulence diffusion and geothermal flux.

The paper investigates the seasonal variability of the vertical turbulent exchange coefficient in the upper stratified layer of the Black Sea. The expedition data used in this work containing information on the microstructure of physical fields were obtained in different hydrological seasons covering the northeastern part of the Black Sea in the Prikerchensky area of the shelf slope. The data were collected during cruises of r/v “Professor Vodyanitsky” in 2016–2019 using “Sigma-1” sounding complex. Based on the semi-empirical methods of assessment of vertical turbulent exchange in the deep-water area of the Black Sea, the dependence of the vertical turbulent diffusion coefficient K on the buoyancy frequency N in the studied layer was established from the flow fluctuation characteristics, with the corresponding graphs and their approximating power-law dependences K  A  N  plotting. In addition, the vertical distribution of the K coefficient with depth was analyzed. Comparative analysis of the obtained dependences with the results of the 1.5D model was carried out. The analysis of the measurement data showed that the results obtained in this work do not contradict the original model. The results can also be used to assess the vertical fluxes of heat, salt and other dissolved chemical and biological substances depending on stratification in the studied part of the Black Sea for different seasons.

The results of experimental studies of the intensity of turbulent exchange in the upper homogeneous layer of the sea and the comparison of field measurements with various models are discussed. Experimental data were collected on a stationary oceanographic platform in the coastal zone of the Black Sea under varied hydrometeorological conditions. A fairly complete set of equipment provided the measurement of basic hydrophysical characteristics (including pulsating values) and background meteorological and hydrological parameters. The turbulent energy dissipation rate was determined from the pulsation spectra of the vertical velocity component using the Kolmogorov hypothesis. Particular attention is paid to the analysis of the influence of the most important mechanisms of turbulence generation, with the completeness of accounting and adequate parameterization of which the objectivity of any model is associated. For verification, we used the well-known models of turbulent exchange for the surface layer of the sea, including the multiscale model of one of the authors of this work. It is noted that the multiscale model, which takes into account the three main mechanisms of turbulence generation, most accurately describes the depth distribution of the dissipation rate in a fairly wide range of hydrometeorological conditions. Its advantage over other models is most pronounced in strong winds, in stormy weather. It is shown that taking into account the actually measured characteristics of the waves and the shear of flow velocity improves the consistency of the multiscale model with experiment.

The results of laboratory studies of the composition and physical properties of span series rocks of the Pribug structure within the eponymous underground gas storage (UGS), have been presented. The rocks are represented by a finegrained quartz sandstone with various sorting and grain roundness, type of cementation and clay content. The character of section suites changes for the material composition of the rocks and their physical properties have been set. The examined properties specify reservoir rocks characteristics which are widely used for integrated geophysics well data interpretation, geological and hydrogeological UGS modeling, making recommendations for increasing efficiency of pore volume usage during gas storage operation. Rock intervals with poor porosity and permeability are detected inside the examined rock series.

The comparison of previously proposed theoretical and semi-empirical approaches for assessing dependence of vertical turbulent exchange on stratification in the natural basins is carried out. The following models are compared: the semi-empirical model based on vertical probing data for revealing dependence of the required parameters on the stratification; the theoretical “spectral” model indicating qualitative differences in the exchange parameters in the “strongly” and “weakly” stratified layers of the main pycnocline in natural basins; the 1.5D model of the Black Sea vertical exchange developed within the framework of the inverse problem. The models, being analyzed in the course of calculating dependence of the energy dissipation rate ε and the diffusion coefficient K upon the buoyancy frequency N, show that they do not contradict each other and, if necessary, can complement each other. In addition, it is found that the greatest physical completeness among the considered models contains the “spectral” model that takes into account a variety of possible distributions in the upper “strongly” stratified layer. However, there are certain difficulties with assessment of the relevant coefficients in, dependencies. The latter problem can be solved within the framework of this approach via proper measurements in the investigated area using the semi-empirical approach relationships. A correspondence between the pair of “spectral” model and semi-empirical model and the 1.5D model for the Black Sea, which will be used in the future, should be also noted.

Physical processes of heat and mass vertical transfer in natural stratified basins depend mostly on the intensity of quasi-inertial internal waves breaking, which, in turn, is determined by the intensity of the wave source and local stratification in the basin. There are many research works including estimations of the dependence of the vertical turbulent diffusion coefficient K on the buoyancy frequency N (stratification). In this paper, on the base of a semiempirical model using the analysis of the pulsation data obtained at probing in the lower stratified part of the Black Sea active layer, the dependence of the coefficient of vertical turbulent diffusion K on the buoyancy frequency N is estimated. The measurements were carried out in the deep area of the basin. The measurement data were collected using a high-resolution probe-turbulimeter “Sigma-1”. A similar dependence for this layer was built based on a 1.5D model of the vertical exchange in the Black Sea deep region. Previously, the same results were obtained in the upper “strongly” stratified and the lower “weakly” stratified layers in the main pycnocline of the investigated basin. The joint analysis of three pairs of power dependencies \( K \cong AN^{\alpha } \) m2s−1 from different stratified layers showed that the exponents α in each pair were very close to each other, while the estimated (semi-empirical) coefficients A in each pair turned out to be much higher than the pattern coefficients.

A detailed analysis of hydrology, hydrodynamics, and microstructure of an anticyclonic eddy is performed. We use the field data obtained in May 2004 at the shelf edge in the northwestern part of the Black Sea. We study the spatial distributions of the Brunt-Vaisal number, and regions of mixing with a vertical scale on the order of 2 m. Possible mechanisms of generation and maintenance of the observed mixed layers are analyzed. A conclusion is made that the investigated eddy in the northwestern part of the Black Sea (possibly similar to the other natural eddies in the northwestern part of the Black Sea) is able to modify the fine layered structure of the scalar hydrophysical fields in the upper 150-m layer forming and maintaining the layers of low vertical gradients with vertical scales of ∼2 m and up to 50–100 km in the horizontal direction owing to the local shear instability of the horizontal flow.

A simple 1.5-dimensional model of vertical exchange for heat, salt, and other dissolved substances has been developed for the Cariaco Basin. The model parameters are derived based on the temperature and salinity data collected monthly at a deepwater station in the eastern part of the basin from 1995 through 2007 during the CARIACO time series program. The model describes the processes of turbulent (eddy) diffusion, which includes the integrated effect of diffusive exchange mechanisms acting in the basin, and of vertical advection, which arises following injection of dense water into deep layers following an inflow from the Caribbean Sea. The model takes into account the changes in the horizontal cross-section area of the basin with respect to depth. Temporal variability is an important feature of the hydrography of the Cariaco Basin. To assess profiles of the vertical eddy diffusion coefficient and vertical advection velocity, we examined a time series of CTD profiles (potential temperature and salinity). Two distinct time intervals were identified as the result of this examination. During the first period, the thermohaline structure of the basin was apparently influenced by one or more inflows. The second period, in contrast, showed little or no influence of an inflow. The data from the second period, where no inflows were observed, were incorporated into corresponding transfer equations to assess the profile of the vertical eddy diffusion coefficient, k(z). Then, the result of this assessment was used with the data from the first period to estimate the profile of the vertical advection velocity, W(z), for a time when the effects of an inflow were evident. For that case, the transfer equations include the terms describing the effect of the inflow. Analysis of the vertical profile of the turbulent diffusion coefficient suggests that, in the upper stratified part of the water column, the diffusion mechanism is mostly associated with transient mixing events, which occur due to shear instability in the field of low frequency internal waves. We speculate that below 400 m bottom friction over the sloping bottom and geothermal heat flux play the decisive role in the vertical exchange. Analysis of the W(z) profiles reveals two layers dominated by the entrainment of the ambient fluid into the down flow of dense water from the Caribbean Sea, and two layers where this down flow breaks down through the formation of isopycnal intrusions.

On the basis of the data of field measurements, we present the results of numerical analysis of the intensity of vertical turbulent exchange in stratified layers of the Black Sea in the region of the shelf–continental-slope boundary depending on the local stratification. The experiments were carried out within the framework of the GEF/BSERP and Black Sea-2004 international projects. The data were obtained by using a probing version of the Sigma-1 measuring complex. In processing the data of measurements, we apply a procedure of evaluation of the coefficient of vertical turbulent diffusion depending on the external conditions based on the analysis of the spectra of the gradient of temperature fluctuations. For the two studied regions of the shelf, the coefficients of turbulent exchange turn out to be much higher (by about an order of magnitude) than for the open sea under similar conditions. This can be explained by the specific features of the bottom topography affecting the dynamics of quasiinertial waves playing to role of the main causes of small-scale mixing and vertical diffusion.

We construct a one-dimensional nonstationary isopycnic model of vertical exchange in the Black Sea with regard for the processes of draining and transformation of waters of the Sea of Marmara (or “plume”), vertical diffusion, and the action of winter convection in the upper layer. It is assumed that mixing in the basin is local in space and time and that the winter wind action remains constant from year to year in the analyzed version of the model. The temperature of the upper mixed layer introduced to simulate the winter conditions is regarded as the principal external variable factor. Within the framework of the accepted restrictions, the model enables us to study the annual and interannual variability of the thermohaline characteristics and hydrochemical parameters in the water column of the sea. As an example, we perform the numerical analysis of the periodic action of external thermal conditions on the characteristics of the system with a period of six years.

We describe a new measuring complex aimed at the investigation of small-scale processes in the upper active layer of the sea. The necessity of creation of a complex of this sort is justified and a circle of problems that can be solved with the help of this complex is described. The scales of resolution of horizontal and vertical inhomogeneities in measuring in the mode of vertical probing are theoretically estimated. The basic technical characteristics of the complex are presented. We also present the results of laboratory and field tests, which confirm the agreement between the calculated and actual technical possibilities of the complex. The structural features of various versions of the “Sigma-1” measuring complex (the “Sigma-1P” point-to-point-operation version and the “Sigma-1Z” probing version) are described.

The ability of the Evpatoria RT-70 radar complex to perform research on space debris was investigated in four trial experiments during 2001-2003. The echo-signals of 25 objects at geostationary, highly elliptical and medium-altitude orbits were recorded on magnetic tapes at radio telescopes in Russia, Italy, China and Poland. The multi-antenna system configuration gives potential to supplement the classic radar data with precise angular observations using the technique of Very Long Baseline Interferometry. The first stage of such processing was fulfilled by the correlator in N. Novgorod, Russia. The cross-correlation of transmitted and received signals was obtained for the 11 objects on the Evpatoria-Bear Lakes, Evpatoria-Urumqi and Evpatoria-Noto baselines. This activity also promoted developing the optical observations of geostationary objects, conducted for the improvement of the radar target ephemerides. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper describes a stationary one-dimensional model of vertical exchange in the Black Sea. The model, formulated within the framework of the inverse problem, is based on the balance of heat, mass of salt and mass of water for the entire basin. The source of salt is the Bosphorus effluent. It is assumed that the process of transformation of the inflow goes in three phases. (i) In the upper layer, the ambient fluid is entrained to the inflow and a plume is formed. (ii) A breakdown of the plume and the formation of isopycnal intrusions and penetration of the plume water into the ambient fluid occur below a certain depth. This depth is found from the analysis of the T, S data. (iii) A part of the plume flows down into the bottom homogeneous layer. The latter phase is important to compensate for the loss of salt from this layer. The influence of the plume on the interior is realised in the form of a source-function distributed over the vertical. The solution describes vertical distributions of eddy diffusivity and vertical velocity in the interior domain of the basin. It is shown that the total upward heat flux from the pycnocline notably exceeds the value of the geothermal heat flux revealing the dependence of thermal conditions in the water column on thermal properties of the plume. The geothermal heat controls thermal regime below the pycnocline, where the plume is a cold water pattern compared with ambient water. The result explains the existence of an intermediate quasi-isothermal layer observed from 500 to 650 m.

The paper discusses the parameters derived through deep-sea precision CTD-probings, characteristic of the structure of the near-bottom boundaries layer, specifically, the depth of the layer's upper boundary and the mean vertical potential temperature/salinity gradients, as well as the density ratio over the layer of the near-bottom convection. The peculiarities of the parameters' spatial distribution have been identified. The conclusion derived from the analysis of the model implies that the near-bottom boundary layer occurs, aside from the presence of the bottom geothermal heat flux, due to the strong dependence of the Bosphorus salt flux on stratification. The dependence of the Black Sea buoyancy flux and vertical diffusion coefficient on depth has been estimated.

Peculiarities of the dynamics and the structure formation in the estuary run-off lenses have been analysed based on field data obtained at the Guinean coast (the central eastern Atlantic Ocean). Attention was paid to the processes of restratification, internal mixing, and exchange in the areas of the frontal zone of the run-off lens and the tidal frontal zone. The stabilization of the front of the estuary run-off lens by means of the periodic ‘washing out’ of its forepart by tidal upwelling is described. The mechanisms of the energy transformation in the leading part of the lens have been revealed. Effects of ‘run-off’ and loczalization of transformed waters in the small-scale frontal zones are found. The energy estimations represented will be useful in considering analogous phenomena in other coastal regions.

The empirical and analytical relationships between the vertical scale of intrusions, which are formed owing to the layering of the mixed boundary layer at a sloping bottom, and the determining parameters are obtained on the basis of field measurements in the coastal zone and energy considerations. An estimate of the vertical diffusion coefficient is given which allows us to determine the role of tidal mixing at the rigid boundaries as a mixing factor for the entire world's oceans.

Field measurements, laboratory modelling, and a hydraulic model indicate that the near-surface stratification formed by heating, freshening by precipitation, and some other factors against the background of a moving surface wedge consisting of a low density fluid over a denser one may result in the appearance of an instability area near the wedge front. The processes of breaking, which occur in the instability area, scatter the wedge energy and participate in frontal zone formation.

The analysis of field data and the results of a one-dimensional model are applied for the description of the deep water structure in the Black Sea. The results of the model support the claim that the observed bottom homogeneous layer exists as a result of the geothermal heat flux and the dependence of mixing properties on stratification. The bottom mixed layer in the Black Sea can only exist if part of the incoming salt penetrates into the bottom layer.