The place of the numerical model of surface waves TRIDWAVE, created in the St. Petersburg Branch of IO RAS, in computational geophysical fluid dynamics is discussed. A description of the mathematical formulation and numerical models of surface waves in the periodic domain for infinite depth is given. The main feature of the model is the ability to switch from a detailed three-dimensional scheme to a simplified two-dimensional scheme, which speeds up calculations by 10–15 times. The statistical characteristics of the results reproduced by the original and accelerated versions of the model coincide with high accuracy. A description is given of the structure of the model, the interaction of its blocks, the scheme for starting and resuming computations and monitoring the results. The dynamic part of the program is described, which carries out the solution at each time step and blocks of operational processing and recording of results that are activated upon request. The system for recording results, their composition is described, and recommendations for expanding the output are given. Recommendations are given for organizing the processing of the results obtained after the end of the calculation.

The paper presents modification of the three-dimensional phase-resolving FWM (Full Wave Model) model of potential waves to simulate the evolution of waves on finite depth water and to determine the range of applicability of the proposed model. Calculations have been carried out to illustrate the fulfillment of the dispersion relation for waves in finite depth, initially assigned by JONSWAP spectrum. The quasi-stationary regime is considered. Calculations were carried out for two resolution options (almost one-dimensional and multidirectional waves) and for various dimensionless depth values. The agreement between theoretical and model calculations of the dispersion relation is shown with a sufficient accuracy on the base of calculated statistic characteristics. The proposed modification of the model is applicable for simulating the multimode wave field for a depth of no less than 0.1 of the maximum wavelength, which significantly expands the field of its application.

The study of surface wave suppression due to oil product films and biogenic films in areas of catastrophic phytoplankton blooms is an important task in application to the problem of remote diagnostics of pollution on the sea surface. The peculiarity of such films in comparison with the well-studied case of quasi-monomolecular films of surfactants is a significant (on the order of or more than 1 micron) film thickness, the latter in this case is described as a layer of viscous liquid. This paper investigates wave damping on a water surface covered by a layer of another viscous fluid of finite thickness with an elastic boundary between them within the framework of linear theory. The features of two different types of wave modes, which for infinitely thin film are characterized as transverse (gravitational-capillary waves, GCW) and longitudinal (Marangoni waves, MW), are numerically analyzed. The evolution of these modes with increasing thickness of the top layer up to thicknesses much larger than the thickness of the viscous sublayer in the film is analyzed. It is shown that in some interval of interface elasticity, determined by the wavelength and viscosity of the top layer, a mutual transformation of the modes occurs at the thickness of the layer of the order of viscous sublayer thickness in the film. Namely, a wave that was GCW for an infinitely thin film, at film thicknesses greater than the thickness of the viscous sublayer, transitions to a MW, and vice versa. This effect arises because the GCW and MW are neither purely gravity-capillary nor purely dilatational. Laboratory experiments showed good agreement with the numerical results and confirmed the existence of the mode transformation effect.

The theory of instability of gravity-capillary waves on the surface of a liquid taking into account linear and nonlinear dispersions is presented. Theoretical research is carried out on the basis of the use of an integrodiffrence operator to describe the linear dispersion of waves. Increments of instability are found. It is shown that the use of an integrodiffrence operator to describe the gravity wave linear dispersion without taking into account their nonlinear dispersion leads to the instability region limitation compared to the case of using the nonlinear Schrödinger equation, but does not change the increment value. The dispersion of the nonlinearity of gravity surface waves reduces increments, especially at large detunes. The structure of instability changes for gravity-capillary waves propagating with minimal phase and group velocities: as the wavelength decreases, the instability region narrows and then disappears. The boundaries of the disappearance of instability area are determined. With a further wavelength decrease, instability occurs again. It acquires the features of “collapse”, when the instability region becomes elliptical. The instability of waves with large wave numbers has a “self-focusing” character, in contrast to the modulation nature of the instability of waves with small wave numbers. Nonlinear dispersion in gravity-capillary waves, as well as in gravity waves, leads to the suppression of instability under large detunes.

The study was based on the results obtained during the expeditions of the R/V “Professor Vodyanitsky” — from November 24 to December 10, 2018 (PV105), from June 4 to 24, 2020 (PV113). New data of light absorption by colored dissolved organic matter (CDOM in the winter and summer were presented. In winter, in the sea surface layer, the light absorption coefficients of CDOM (a_CDOM(438)) (0.10 ± 0.015 m^–1), exceeded summer values (0.062 ± 0.025 m^–1). There were no seasonal differences in the mean spectral slope (S_CDOM) values (0.019 nm^–1). However, the variability of S_CDOM values in summer is noted in a wider range (0.015 to 0.026 nm^–1) than in winter (0.017–0.021 nm^–1). The highest S_CDOM values are resulted from photodestruction of CDOM in the sea surface layer in summer. An inverse relationship has been revealed between a_CDOM(438) and S_CDOM, which is described by a power law. Seasonal differences in the content of chlorophyll a (TChl-a) in the upper mixed layer (1.1 ± 0.43 mg m^–3 in winter and 0.32 ± 0.11 mg m^–3 in summer) and in the type of the TChl-a vertical distribution, due to the water hydrological structure, were shown: in winter — uniform distribution within the upper mixed layer, which was comparable to or exceeded the photosynthesis zone, in summer — the presence of a layer of deep chlorophyll a maximum near the bottom of the euphotic zone. Relationship between a_CDOM(438) and S_CDOM was not revealed for both seasons.

According to observations over the past 20 years, the oligotrophic Lake Teletskoye (Altai Republic) is undergoing gradual eutrophication, showing the necessity of regular monitoring of its ecological state. In August 2023, multiparametric hydrooptical studies were carried out on Lake Teletskoye, including measurements of the spectral water upwelling radiance reflectance and underwater irradiance, as well as sampling for laboratory determination of chlorophyll a concentration. In the main part of the lake, spectral maxima of reflectance coefficient were observed to be 0.7–1 %, while in estuary areas of Chulyshman, Kokshi, Kyga rivers where the influence of suspended matter is significant the reflectance reached 2.8 %. The performance of the semi-analytical biooptical algorithm for calculating the chlorophyll a concentration from the reflectance spectra, adapted to the conditions of inland waters, was tested. An overestimation of the calculation results compared to the measured chlorophyll a concentration was shown, however, a significant correlation was observed between them. In addition, the spectra of the light diffuse attenuation coefficient were calculated from both the reflectance spectra and underwater irradiance, showing good agreement. The main optically significant component of Lake Teletskoye water is nonliving organic matter, which is consistent with the data of direct laboratory determinations. The semi-analytical algorithm shows the possibilities of optical measurements for describing the ecological state of inland water bodies and can be the first step towards bio-optical satellite monitoring of Lake Teletskoye.

The presented paper opens a series of articles devoted to studies of the bio-optical characteristics of the Volga waters in the context of creating regional bio-optical models accounting the transformation of the water optical properties from north to south. The preliminary results of field measurements carried out in 2023 at the middle Volga are presented. Measurements were performed with high spatial resolution — 3 m. The spatial distributions and variations of various hydro-optical and hydrological characteristics, including water brightness spectra and the content of dissolved and suspended substances that determine its color (chlorophyll a, suspended solids), data on water temperature, electrical conductivity, salinity, dissolved oxygen content, flow velocity and direction, were investigated at different spatial scales. The influence of different Volga tributaries was assessed, including the seasonal variability of bio-optical characteristics in the areas of the confluence of the Volga and Oka, and the Volga and Kama. Cross-correlation estimates were given. The obtained results expand an actual picture of the studied water area and will be used in the analysis of satellite data and the development of bio-optical models.

Data on the current structure in most reservoirs of the Volga Cascade were obtained in the last century and correctly describe the current structure only in general terms. The paper presents current structures at different distances from the HPPs in the Gorky, Cheboksary, Kuibyshev, and Volgograd reservoirs. The present work is a brief review of the existing database of current measurements in the water area of the Volga Cascade reservoirs. The data were obtained during field measurements in 2023 and 2024 using an acoustic current profiler. Longitudinal sections of the river part of the Cheboksarsky and Kuibyshev reservoirs, spatial structures of currents in the lake parts of the considered reservoirs are demonstrated. It is shown that the average current velocity in the river part of the reservoir decreases with distance from the HPP dam. The structure of currents in the lake part of the reservoir has high variability depending on the flow regime through the HPP. Local features of currents related to flow regulation at hydrosystems are presented, which include formation of whirlpools, changes in velocity and current directions.

The International Geophysical Year, held in 1957–1958, became an important event for conducting hydrophysical observations of the world ocean. Successful participation of Soviet scientists in its events became possible due to state support for research institutes, direction for research of research vessels, purchase and production of necessary equipment. The greatest contribution was made by the research vessels “Mikhail Lomonosov” and “Vityaz” used in the research. Deep-sea vehicles, sea buoys, space satellites were widely used in the research, which made it possible to clarify the nature of sea currents, causes of tsunamis and other issues of marine hydrophysics. It was also important that Soviet scientists attracted scientists from the countries of the Council for Mutual Economic Assistance and other friendly countries to the research.