Vol 40, No 4 (2024)

Purpose. Sea breeze circulation is a common mesoscale phenomenon near the coasts of water bodies. However, at the moment, a number of the published review papers on this topic remain small. Therefore, the purpose of the work is to complement the existing reviews on sea breezes by generalizing the available knowledge on the influence of air heating intensity near the land surface, atmosphere stratification, synoptic background wind and the Coriolis force upon the sea breeze circulation.

Methods and Results. An overview of the results of studies involving the theoretical research methods, namely linear theory and two-dimensional numerical modeling, is presented. At first, the sea breeze circulation is considered within the framework of linear theory. Further, a technical description of two-dimensional models and the breeze features obtained applying these models are presented. The published works having been reviewed made it possible to consider the influence of four main factors (heat flux, atmosphere stratification, background wind and the Coriolis force) upon the breeze circulation.

Conclusions. Within the framework of linear theory, the breeze circulation represents an internal inertial-gravity wave with a daily period. Depending on the uniformity of vertical profile of the background synoptic wind, its influence on the linear sea breeze circulation leads to the asymmetry of circulation relative to the coast and to limitation of the breeze height. In a nonlinear regime, the important feature of breeze circulation obtained by applying numerical simulation consists in formation of a gravity current propagating over the surface. The nonlinear regime implies a fairly clear dependence of the velocity of gravity current front propagation on its height. The main manifestation of the background wind influence upon the gravity current is the change in its height that results in formation of a stationary or rapidly spreading current. Due to the Coriolis force influence, both within the framework of linear theory and in the nonlinear regime, an along-coastal velocity component is formed that leads to a decrease of the velocity component perpendicular to the coastline.

Purpose. The aim of the study is to analyze the features of mean long-term structure and intra-annual variability of the characteristics of temperature fronts on the ocean surface in the Patagonian shelf region.

Methods and Results. Daily average values of the ocean surface temperature from the NOAA OI SST data and the geostrophic velocity components on the surface at the nodes of a 0.25° regular grid from the CMEMS reanalysis for 1993–2020 were used. It is shown that at the western periphery of a large-scale cyclonic meander formed by the currents in the Patagonian shelf region (south of 45° S), three branches of the Subantarctic Front are traced; they correspond to the West Falkland Current and to two jets of the East Falkland Current. North of 45° S, where one Falkland Current jet is observed, one branch of the Subantarctic Front is identified. On the eastern periphery of the meander, the front corresponding to the common stream of the Brazil Current and the Falkland Return Current is revealed. Besides, south of 40° S, a separate branch of the Subantarctic Front corresponding to one more recirculation of the Falkland Current is observed. It is shown that at the meander western periphery, the branches of the Subantarctic Front are most intensified in February – March, at its eastern periphery – in March – April, and at the meander northern peak (in the zone of the Brazil – Falkland Confluence) – in April – May and November.

Conclusions. It is found that on the western periphery of the cyclonic meander, south of 45° S, the main branch of the Subantarctic Front approximately follows the 900–1000 m isobaths, north of 45°S – the 150–170 m isobaths, and closer to the Brazil – Falkland Confluence – the 50–60 m isobaths. At the meander eastern periphery, north of 40° S, the main branch of the front is very close to the 800–1000 m isobaths, south of 40°S – to the 1000–2500 m isobaths. It has been established that the differences between the seasonal cycles of intensity of the Subantarctic Front branches are related to the dissimilar warming and cooling rates of surface waters separated by these branches.

Purpose. Development of regional satellite algorithms requires the information on bio-optical properties of a particular water area. The present study is aimed at comparative analyzing the bio-optical properties of optically complex waters differing in their trophic status.

Methods and Results. The study combined the results of measuring the spectral bio-optical properties in the waters of the Black, Azov, Barents and Norwegian seas, the Arctic and Southern oceans (Atlantic sector), and the Baikal and Teletskoye lakes. Spectral coefficients of light absorption by phytoplankton, non-algal particles and colored dissolved organic matter were measured in accordance with the International Ocean Colour Coordinating Group Protocols. The study areas included the waters with trophic levels from the oligotrophic to eutrophic ones (the chlorophyll a concentrations in the surface layers varied from 0.066 to 24 mg×m⁻³), and with high heterogeneity in their bio-optical properties: the total non-water light absorption at the wavelength 438 nm varied from 0.021 to 0.97 m⁻¹.

Conclusions. In all the regions, a high (within an order of magnitude or higher) spatial variability in the values of light absorption coefficients by all the optically active environment components and their ratios was noted. This fact indicates the optical complexity of waters in each of the regions under study. The regional specificity of parameterization coefficients for light absorption by phytoplankton, non-algal particles and colored dissolved organic matter was shown. The revealed parameterization coefficients for light absorption by the optically active components can be used to develop the regional satellite algorithms for assessing water quality and productivity indicators. Based on the empirically revealed dependencies, the following additional indicators of water quality were proposed: the euphotic zone depth and the spectral characteristics of downwelling irradiance which can be retrieved based on remote sensing data.

Purpose. The work is aimed at studying the statistics of width-to-length ratio of a breaking crest for an active phase of wind wave breakings, and at assessing the possibility of approximating the geometric shape of a breaking crest with an ellipse.

Methods and Results. The experimental data including the video records of sea surface and the wind speed measurements were obtained at the stationary oceanographic platform in the Black Sea hydrophysical subsatellite polygon (Katsiveli, the Southern Сoast of Crimea) in 2015–2019. Processing the in situ data made it possible to form the arrays both of lengths and areas of the breaking crests, and the synchronous measurements of wind speed.

Conclusions. The distributions of random variables proportional to the minor-to-major axes ratios of breaking crests are obtained; it is shown that these distributions are coincident for the whitecaps of different scales. This fact testifies to the similarity of whitecap geometric shapes. The average value of the breaking crests’ axis ratio obtained from all the data is 0.41. It is concluded that the average geometric shape of the breaking crest boundaries is satisfactorily described by an ellipse with the eccentricity 0.91. The ratio of the speed of a breaking crest’s centroid to that of its anterior front is estimated to be 0.9.

Purpose. The research is purposed at substantiation of the design of floating marine stations with a wave energy generator. The proposed construction is of higher efficiency as compared to the known designs due to the application of roll and resonant operating mode.

Methods and Results. The resonant method of converting wave energy into electrical energy, as well as the design of an autonomous station based on the resonant conversion of the station’s body roll into the electrical energy are described. The method implies adjusting the frequency of natural angular oscillations of the floating station's body to the significant wave frequency. It has been theoretically proved that the conversion of roll energy is more effective than the conversion of vertical oscillations. This is due to the fact that the amount of damping during vertical vibrations of a cylindrical body in water exceeds the amount of damping during angular oscillations of such a body. Besides, the proposed method is shown to be effective for applications in the development of measurement systems and storage devices. The design of a floating station is proposed for implementing the resonant method for converting wave energy. It is shown that adjusting the frequency of natural onboard oscillations of the station body to the significant wave frequency can be done using the additional filled tanks. The algorithm for adjusting the body roll oscillations to the resonance with significant wave frequency is described. The kinematic scheme for a mechanical converter of rolling energy into electrical one is proposed.

Conclusions. The results of theoretical studies were validated experimentally using the device test model in a wave experimental basin. They show that the hydrodynamic efficiency of the proposed wave converter increases as the wave heights decrease.