Barotropic saline Baltic inflows (SBIs) occurred in the period of 01.09.2023–20.02.2024 are analyzed using the NEMO reanalysis data. To test the model product, it is shown that it adequately reproduces the observed time series of salinity and temperature on depth and time of 32 yr long (1993–2024) at a monitoring station BY15 located in the Gotland Deep. The water volume imported to the Baltic Sea with the SBIs being estimated from the in situ observations of the sea level and salinity is found to be highly correlated with the direct estimates based on the NEMO reanalysis data. Comparison of the October and December 2023 SBIs reveals that quantitative characteristics of an SBI, such as the imported water volume and salt mass, being important nevertheless do not fully determine the subsequent evolution of the salinity field in the remote basins of the Baltic Sea. Apart from the imported water volume and salt mass the synoptic variability of the wind field is of paramount importance. Keeping in mind that the salt water transport in the bottom layer of the Bornholm Channel, Słupsk Furrow, and Hoburg Channel towards the deepest Baltic basins is most intense at northwesterly, northerly, and northwesterly winds, respectively, one may expect that a long-lasting northwesterly wind period immediately following the inflow event is the most favorable for ventilation of the Baltic Sea deep layer.

At the Atlantic Branch of P.P. Shirshov Institute of Oceanology of the Russian Academy of Sciences, an autonomous thermistor chain was developed and manufactured using a modular design. Measurements conducted on the eastern slope of the Gdańsk Basin (Baltic Sea) revealed fluctuations in isotherms. Interpretation of the permanent halocline oscillations showed that their upward shift is primarily caused by events in which anticyclonic circulation in the water column generates a compensatory current in the bottom layer. This compensatory current, flowing eastward along the southern slope of the Gdańsk Basin, lifts the isotherms near the eastern slope. The highest correlation between the depth of the 5.5 °C isotherm and the projection of the wind stress vector was observed under westerly winds with a slight northerly component, with a time lag of 38–48 hours. This delay is attributed to the system’s inertia. Field measurements were also used to validate the NEMO model data, revealing model inaccuracies: a time lag and smoothing of fluctuations. The most significant discrepancies were observed in the upper part of the temperature sensor string, where the model failed to reproduce high-frequency oscillations. Near the bottom, high-frequency fluctuations diminish, and the model reproduces the vertical movements of the selected isotherm with reasonable accuracy, though still with a delay.

The paper considers the causes of underestimation of bottom salinity in the general circulation models of the Baltic Sea. The highly efficient Oceananigans model is used to calculate the propagation of the inflow of saline North Sea waters in the bottom layer of the Baltic Sea in the period January-April 1993. The results of these calculations are in better agreement with the V.T. Paka high-frequency scanning data of the vertical structure of the sea with a vertical resolution of 0.25 to 0.5 m and distances between stations of about 500 m than the results of a similar calculation (reanalysis) for the same situation performed using the NEMO-Nordic model. This was achieved by significantly reducing numerical diffusion by increasing the vertical resolution and using high-order advection schemes in the Oceananigans model without using the observational data assimilation procedure. The above improvements to the Oceananigans model reduced the calculation speed by only 30 %. The developed model configuration gives certain hope for obtaining, without the assimilation procedure, adequate estimates of the propagation of the bottom gravity density current in the Baltic Sea and its interaction with sediments, including oxygen exchange, which is important for modeling marine ecosystems.

Based on the analysis of sea level data from seven coastal tide gauges, the resonance mechanism of diurnal tide formation in the Gulf of Finland was investigated. The main role in the formation of the tidal regime in the Baltic Sea is played by the independent tide, the response of the water column of the basin to the direct impact of the tide-generating forces. An important feature of the tide in the Baltic Sea is the predominance of diurnal tides over semidiurnal ones. It was found that the closer the frequency of the tidal harmonic to the natural frequency of the basin, the stronger the equilibrium response of this tidal harmonic. Such resonance increase in the tidal diurnal components is caused by tidal resonance, the influence of natural oscillations of the Gulf of Finland and the entire Baltic Sea with a period of about 27 hours. It is the presence of resonant amplification of diurnal tidal oscillations in the Gulf of Finland that leads to the fact that the maximum tidal range in this part of the sea reaches 19 cm.

Based on a coupled high-resolution numerical model, changes in the current structure and wind wave field in the northeastern part of the Neva Bay adjacent to the 300th Anniversary Park of St. Petersburg caused by coastal hydrotechnical constructions have been analysed. Using August 2011 conditions, it has been shown that under weak winds conditions, the River Neva runoff is the main contributor to the formation of the current field in this region. The influence of coastal constructions is manifested in the destruction of an anticyclonic vortex near the hydrotechnical structure No. 3 and a in a decrease of current velocity from 15 cm/s to 5 cm/s. For December 2011 conditions, it has been found that under weak southwestern and western winds, the influence of coastal constructions is expressed in a decrease of current velocity by 5–10 cm/s in the beach zone of the park while maintaining the overall structure of the current field. During stormy westerly winds, typical of late December 2011, a considerable southward deflection of the Neva outflow occurs, reducing the outflow current velocity to 20–25 cm/s. At the same time, a current directed along the shoreline from the northwest to the southeast forms in the beach area. The influence of coastal structures in this case leads to a decrease in current velocity by 5 cm/s in the area between hydrotechnical structures No. 2 and No. 3, resulting in the formation of a stagnant zone. Analysis of the wave regime has revealed that coastal constructions create wave shadow zones, thus significantly reducing wave heights in their immediate vicinity, though the protective effect is limited to localised areas. The maximum decrease in wave activity due to the presence of coastal constructions is observed under westerly winds, while the minimum occurs under southerly winds.

A series of experiments were carried out on mixing a water layer with an initially constant vertical salinity (density) gradient using oscillating vertical rods, creating a uniform turbulent effect throughout the entire thickness of the water layer. As a result of mixing, in most experiments a stepwise structure was formed, in the form of a sequence of quasi-homogeneous layers separated by highly gradient interlayers. The stepped structure in the density field was observed using a shadow device (schlieren method). In some experiments, the stepped structure was not formed, and stratification, despite mixing, was characterized by a constant vertical density gradient. In each experiment with stratification, measurements of the thicknesses of quasi-homogeneous layers were made. A self-similar dependence of the dimensionless layer thickness on the Richardson number was established. In dimensional form, this dependence indicates that the thickness of the quasi-homogeneous layer is proportional to the product of the amplitude of the oscillation of the rods by the ratio of the kinetic energy of the turbulent effect to the potential energy of stratification. A diagram is presented that allows one to judge the regularity of layer formation at different values of Reynolds and Richardson numbers. The experiments conducted have shown that not only differential-diffusion convection, but also prolonged mechanical mixing under certain conditions can lead to stepwise stratification of a stably stratified aqueous medium.

The paper describes the data set of measurements of sea level oscillations with a discreteness of 1 minute in three bays of Sevastopol: Gollandiya, Karantinnaya and Krouglaya. The period from early October to mid-December, which is the most provided with synchronous measurements, was analyzed in detail. Spectral and wavelet analysis allowed us to confirm the manifestations of the previously described tidal oscillations, as well as the Black Sea seiche. A more detailed analysis of spectral and phase diagrams allowed us to describe the periods at which local eigenmodes are manifested. It is shown that in the considered bays the oscillations caused by tides, global seiches of the Black Sea and shelf seiches occur in-phase. The interaction of the bays on their own periods has an antiphase character. For the first time on the field observations for the Sevastopol bay system, it was shown how the senior modes of a larger bay manifest themselves in the oscillations of adjacent smaller bays. High values of coherence were noted between the oscillations in the Gollandiya and Karantinnaya Bays at the natural periods of Sevastopol bay equal to 48 and 10 min. Krouglaya and Karantinnaya Bays actively interact with each other at the Helmholtz mode periods (11.9 min — Helmholtz mode period of Karantinnaya Bay; 13.5 min — Helmholtz mode period of Krouglaya Bay).

The objective of this study is to assess the accuracy of reproducing the vertical distribution of temperature and salinity in the waters of Avacha Bay (the Pacific Ocean) in the coastal area, based on data from two global ocean reanalysis products: CMEMS GLORYS12v1 and GOFS3.1. The results of in situ measurements performed on a repeating grid of stations in April 2019 and 2020 were used as independent data. The results showed that both products reproduce the general trends in thermohaline characteristics, but the accuracy varies depending on the depth and area. The average temperature anomaly was 0.6 °C for CMEMS GLORYS12v1 and 0.4 °C for GOFS3.1, and for salinity — 0.3 and 0.4, respectively. The largest deviations were observed at the shelf stations, where the reanalysis products failed to reproduce both the mean values and the near-surface halocline. This is likely due to limitations in the models’ resolution and a lack of sufficient data for accurate calculations. In the deepwater part of the bay, both products demonstrate higher accuracy, although inaccuracies in reproducing the characteristics and features of the vertical structure of the cold intermediate layer and the upper boundary of the warm intermediate layer are noted at individual stations. In particular, GLORYS12v1 reproduces the salinity distribution better, whereas GOFS3.1 more accurately reflects the temperature structure. However, both products demonstrate poor accuracy in reproducing the vertical structure of salinity on the shelf, which indicates the need for more accurate accounting of local processes such as freshwater runoff and the dynamics of coastal currents. In general, it is preferable to use temperature and salinity data from the GOFS3.1 product to track the state of marine ecosystems in the deep-water areas of Avacha Bay, including the “Northern” canyon area, which is the epicenter of spawning of the East Kamchatka pollock population.

Microelectromechanical inertial sensors with embedded attitude determination algorithms have become standard in modern wave measurement buoys, though their proprietary nature often limits transparency in evaluating wave parameter accuracy. This paper presents the results of a field experiment with a prototype wave measuring buoy, in which raw triaxial accelerometer, gyroscope, and magnetometer data were recorded onto a memory card with minimal preprocessing. Subsequent post-processing was performed using various attitude estimation algorithms with open-source and easily accessible software implementations. The study examined both direct methods based on gravity and magnetic field measurements and more complex approaches, including the complementary filter and its variations (Mahony and Madgwick filters), as well as the Kalman filter and its extended version. The resulting attitude estimates enabled computation of both spectral wave characteristics and bulk parameters including significant wave height, peak period and mean direction. Comparative analysis against reference resistive wave gauge measurements revealed algorithm-dependent performance in the context of sea wave measurement. These findings offer practical insights for scenarios requiring either post-processing of raw buoy data or development of optimized embedded systems where full raw data transmission is not feasible.

The article provides an overview of the main innovations that were developed and implemented in the practice of in situ hydrophysical measurements in the ocean by Vadim Timofeevich Paka. Among them are the thermochain, the thermotrawl, the loosely tethered microstructure probe “Baklan”, the undulating towed fine-structure system “Rybka” with undulation control by a high-speed winch, and the current velocity meter based on the inclination angles of a body with positive buoyancy suspended in the oncoming flow (Tilt Current Meter — TCM). Special attention is paid to the “Baklan” probe and the “Rybka” system, since they had the greatest influence on the development of modern methods of in situ measurements in the ocean and had the largest number of followers. The general idea of the “Baklan” probe was a quasi-free immersion of the carrier of turbulence sensors on a flexible, unloaded, free-falling cable with near-neutral buoyancy. This made it possible to quickly perform multiple measurements of turbulence in the upper layer of the ocean at a low level of noise, which was impossible when using both ordinary cable probes and autonomous free-falling probes. The article presents the history of the development of V.T. Paka’s ideas, which formed the basis of “Baklan” and “Rybka”, and their implementation in hardware. A comparison of “Baklan” and “Rybka” with existing measurement systems such as MSS Profiler and SeaSoar is given.