This article presents an algorithm for estimating the vertical displacements of isopycn and horizontal current velocities caused by internal tidal borings from their manifestations in the roughness field on satellite images of the Banda Sea. The calculation algorithm is formulated within the framework of the Korteweg-de Vries equation (KdV), augmented with a term taking into account the cylindrical divergence. The coefficients of the KdV equation — quadratic nonlinearity, dispersion and tidal linear internal wave velocity — were calculated using the mean — climatic density profile in the Banda Sea. The leading soliton velocity and wavelength in the rear zone of the internal tidal borings were determined from satellite images. Using the proposed methodology, estimates of the maximum vertical displacement of the pycnocline/maximum amplitude of the leading soliton and the maximum velocity of surface currents induced by the internal tidal borings were obtained. It follows from the analysis of satellite images that the internal tidal borings in the Banda Sea are transformed under the action not only of nonlinearity and dispersion, but also of cylindrical divergence. It is shown in the framework of the knoidal model of internal tidal borings that in the process of evolution the energy of its leading and subsequent waves is attenuated due to the cylindrical divergence. This attenuation is estimated when the leading soliton travels a distance equal to twice the tidal period.

The article is devoted to obtaining long-term physical and geographical characteristics of the River Plume frontal zone as a separate hydrological structure that forms at the boundary of the fresh surface layer of the Ob and Yenisei Rivers. The primary data for identifying the frontal zone are satellite measurements of surface temperature (MODIS Aqua, Suomi NPP-VIIRS), surface salinity (NASA SMAP) and sea level (AVISO) for the period from July to October from 2002 to 2020. The position and characteristics of the River Plume frontal zone were determined using cluster analysis, which was applied for the first time to an integrated set of remote satellite sensing data in this region. The results of the study showed that in the warm period of the year, the average long-term surface temperature gradient of the River Plume frontal zone was 0.08 °C/km, the surface salinity gradient was 0.1 PSU/km, and the area was 155,000 km². During the ice-free period of the second decade of the 21st century, the temperature gradient of the frontal zone weakens by 0.04 °C/km, and the area decreases by 100,000 km². The correlation analysis showed that the temperature and salinity gradients, as well as the area of the River Plume frontal zone, were determined by the volumes of the river discharge of the Ob and Yenisei and ice parameters in the warm period of the year. The article presents the obtained estimates of the relationship between the characteristics of the frontal zone and the volume of river discharge, ice cover and wind parameters, as well as the value of the atmospheric indices of the Scandinavian oscillation (SCAND). 

The analysis of long-term seasonal changes in the concentration of chlorophyll, the maximum rate of phytoplankton photosynthesis and water temperature in the surface layer of the open waters Black Sea from 1998 to 2015 has been carried out. The trends of these indicators were assessed. For the research, we used the data of satellite observations SeaWiFS and MODIS-Aqua, MODIS-Terra. Typical positive temperature trends of 4 % in the deep-water western part of the sea. An annual temperature rise in deep-water areas was noted in the western cyclonic circulation by 0.038 °C. According to average annual data in other areas, no increase was found. The increase was mainly due to the winter season. Negative trends of primary phytoplankton production within 16.4–18.6 % of the initial level according to average annual values throughout the deep-water area. Significance level — p < 0.1. A decrease in primary production was observed in the summer. There were no statistically significant directional changes in 

chlorophyll concentration based on averaged data over 18 years. In different parts of the deep-sea area, the direction of interannual and seasonal changes in all indicators was similar. The emerging trend towards a decrease in phytoplankton productivity in recent years may lead to a restructuring of the phytoplankton community.

The influence of water dynamics on the spatial distribution of chlorophyll a fluorescence intensity in the surface layer of the Barents and Norwegian Seas, obtained during the 80-th cruise of the R/V “Akademik Mstislav Keldysh” using the flow-through measuring complex in August 2020, was demonstrated. The divergence of the current velocity field, calculated according to reanalysis data, was chosen as a parameter describing the dynamics of water masses. The application of the sliding correlations method allowed us to identify areas of the track with positive and negative correlations between the values of divergence and chlorophyll a fluorescence intensity. It is shown that a positive correlation is formed as a result of the vertical movement of the water surface layer, a negative one — may be a consequence of the water masses advection and the daily changes of the values of photosynthetically active radiation. The part of obtained results is confirmed by satellite data on the spatial distribution of chlorophyll a concentration.

In this paper we present the results of a laboratory experiment simulating the mechanisms of a surfactant film localization under the action of periodic surface waves. It is shown that the film compressed by a surface wave, can be conditionally divided into three sections — the dense film region as the most distant from the wave source, the area of a diluted film and the region of relatively clean water. The paper is focused on the processes occurring in the diluted film region characterized by the transition from clean water to the dense film, where horizontal circulation currents are registered. The character of currents is varying depending on the wave amplitude so that the divergent circulation cells occur at small and large wave amplitudes, but at medium amplitudes the roller currents forming a convergence zone on the basin axis are observed. The experimentally obtained stationary distribution of surfactant concentration is compared with the previously developed model of film compression due to surface tension induced by waves. The comparison shows good agreement between the theory and the experimental results at small and large wave amplitudes. Their discrepancy at medium wave amplitudes in the diluted film region is presumably related to the presence of convergent cells which are not considered in the model.

Estimates of methane emission from the Mozhaysk reservoir surface were carried out using the mathematical model LAKE2.3. The average emission value is 361 tC per year, the average flux = 37.7 mgC–CH₄ m^–2 day^–1. Comparison of the obtained estimates with in situ measurements revealed, that the methane emission and specific flux according to the model are in good agreement with the observations data. The ebullition makes the largest contribution to the total emission. During the heating period, an increase of methane emission is observed with a maximum before the autumn mixing stage. In the course of numerical experiments with the model, it was found that the amplitude of methane fluxes into the atmosphere is associated with fluctuations in atmospheric pressure, and the most significant emissions peaks associated with water level drawdowns. Effective method for calibrating the diffusion component of the methane flux into the atmosphere is the potential rate of methane oxidation in the Michaelis-Menten reaction, and for ebullition it is the methane generation parameter in bottom sediments — q₁₀. For the described numerical experiments, the article presents the values of the annual emissions of methane into the atmosphere. 

One of the problems in the design of ports is the assessment of coastal sediment movements near structures. The article presents materials for assessing the impact of port facilities on the processes of coastal erosion/accumulations in the area of Gelendzhik Bay (Black Sea). All the main processes of interaction of waves, currents and sediment movement occur in the coastal zone, therefore, the study presents the possibilities of complex application of hydrodynamic and lithodynamic models. In this work, the wind wave models Wave Watch III and SWAN were used. As the initial data, the data of the NCEP/NCAR reanalysis of wind fields in the period from 1989 to 2012 were used. To simulate currents, sediment transport and lithodynamic processes, a model of two-dimensional COASTOX–CUR currents generated by waves and wind, COASTOX-SED sediment transport together with the COASTOX–MORPHO bottom reshaping model was used. In the simulation scenario, a sequence of the 5 strongest storms from the period under consideration was considered. Analysis of washout zones/accumulations have shown that areas of intensive bottom reshaping are associated with the most intense currents. It is shown that the construction of the port facilities will not have a significant impact on the lithodynamic processes in the Gelendjik bay.

Amplitude modulation of a noise signal of the surface ship is formed both directly at noise emission, when the line of the shaft and the propeller is rotating, and in addition due to the ship rolling and pitching caused by the rough sea. At the same time additional low-frequency (no more than 0,2 Hz) amplitude modulation of the noise emission can be observed as a process of temporary variations of the received signal power. In this regard, it is interesting to find relation of the amplitude-phase modulation spectrum of the ship broadband signal at its rolling and pitching with the spectrum of rolling and pitching process. As a mechanism of formation of the noise signal modulation at the ship rolling and pitching the fluctuating interference of the beams, propagating from vertically dipping underwater point source near the water surface, is considered. The analytical ratios connecting the amplitude-phase modulation spectrum of the ship broadband signal at its rolling and pitching with the spectrum of rolling and pitching process are received.

As a result, the parameter describing cumulative conditions by which it is possible to determine spectral properties of modulation is determined. The type of the power variation spectrum can be substantially different depending on values of parameter K = 2kσ_H sinα 1 where k — the wave number, σ_H-root mean square value of the vertical component (source shift) due to rolling and pitching, α — the beam grazing angle at the surface. At value 2kσ_Hsinα< 1 results of observation of the signal modulation process can be identified with process of the ship rolling and pitching. At value 2kσ_Hsinα> 1 the signal modulation spectrum will not correspond to the spectrum of rolling and pitching process. With the increase of parameter K value the modulation spectrum extends, goes beyond the spectrum of rolling and pitching process. Significantly lower and high harmonics emerge. Results of computer modeling and natural experiments confirmed dependence of the type of the modulation spectrum on parameter K. Thus, presence of the additional mechanism of noise signal modulation formation at the ship rolling and pitching, caused by the phenomenon of fluctuating interference of the beams propagating from vertically dipping underwater point source near the water surface is found.

The paper proposes a variant of choosing the optimal solution to the large-scale scientific, technical and ecological-economic problem of the European part of the Russian Federation based on the integrated use of results of numerical modeling of hydrodynamic processes, expert environmental assessments and rating economic comparison.

The object of scientific research is the section of the Volga River from the Gorodetsky hydroelectric complex to Nizhny Novgorod (from 852.5 to 899 km along the ship’s course). The purpose of the work is to prepare proposals for the choice of an option for improving navigation conditions on the Volga River section under consideration in the lower reaches of the Gorodetsky locks under various flow regimes through the Gorodetsky hydroelectric complex, taking into account the priorities of environmental protection, protection of water bodies and use of water resources established by legislation. As a result of the work, a variant of the project proposed for implementation on the territory of the Nizhny Novgorod region for the rational solution of navigation problems on the Volga River, taking into account the assessment of the impact on the sanitary-epidemiological and environmental situation in the region, flooding and flooding zones. The project includes the construction of a third parallel lock in the area of Gorodetsky locks No. 15–16 and the creation of a navigable slot with a guaranteed fairway depth of 4.0 m.

The height of one of the most outstanding floods of the Neva on September 10 (21), 1777 is practically not captured on the walls of buildings and structures in St. Petersburg. In this context, the leveling catalog, which reflects more than 700 height marks of this flood, and plans with the location of these marks within St. Petersburg, seems to be absolutely unique and very relevant. The author of the catalog is Friedrich Wilhelm Bauer, quartermaster general, surveyor, cartographer. Work on leveling the flooded urban areas was carried out at the behest of Catherine II. In the leveling catalog of F.V. Bauer notes that the maximum height of the water in the flood of 1777 reached 10 feet 3 inches and that it was measured from the ordinary of the Admiralty footstock. To measure excess F.V. Bauer used the French linear measure, which made it possible to recalculate the maximum flood height to a value of 333 cm.