Morskoj gidrofizičeskij žurnal

Purpose. The work is aimed at studying the changes in thermal structure of the Black Sea upper layer during seasonal winter cooling in 2009−2010.

Methods and Results. The NEMO-OASIS-WRF (NOW) coupled sea-atmosphere mesoscale model with the 2 km horizontal resolution is used. The changes in the sea upper layer during the 01.12.2009–28.02.2010 period are reproduced and the temporal variability of water temperature at different depths is considered. For a characteristic point in the deep-sea part, it has been shown that the upper mixed layer thickness increased with time, whereas the cold intermediate layer upper boundary lowered as aresult of the entrainment of colder water from below to the upper warmer mixed layer. It is also indicated that lowering of the cold intermediate layer upper boundary is accompanied by an increase of its temperature. In order to describe the cold intermediate layer evolution during winter cooling, two criteria are proposed: minimum water temperature in the 0−120 m layer and difference between this value and the sea surface temperature. Vertical temperature profiles at different stages of winter cooling are obtained and the main changes in thermal structure of the sea upper layer are considered. It is particularly shown that in course of winter cooling, the cold but less salty water at the northwestern shelf does not mix with the open sea waters due to a large horizontal density gradient.

Conclusions. When describing the seasonal winter changes in the upper mixed layer, it is necessary to take into account not only heat transfer to the atmosphere through its upper boundary, but also the vertical turbulent exchange through its lower boundary. The heat accumulated during summer in the upper mixed layer is transferred not only to the atmosphere; its small part also goes to the lower levels, which leads to an increase of the cold intermediate layer temperature. The influence of boundary conditions, namely the inflow of waters with different features from the Marmara Sea, can result in the formation of areas where the cold intermediate layer, though formally absent as a layer between two 8°С isotherms, exists as an intermediate layer of colder (by 3−4°С) water as compared to the upper mixed layer. During the period under consideration, vertical mixing including the transfer of warmer and less salty waters from the upper mixed layer to the lower ones was most intensive in the western part of the sea. This fact is assumed to be a result of the inhomogeneous sea cooling: heat flux directed from the sea surface to the atmosphere decreases from 200 W/m² in the northwestern part of the sea up to 50W/m² in its southeastern part.

Purpose. The purpose of the study is to consider both features of storms in the attenuation stage as a factor in the coastal profile restoration after storm erosion and a potential cause of seasonal deformations.

Methods and Results. Seasonal morphodynamics of accumulative coastal areas was studied in the regions both of the Vistula Spit (South-Eastern Baltic) based on the monitoring measurements of coastal profile performed by the employees of the Shirshov Institute of Oceanology, RAS, from May 2019 to March 2022 and the Oktyabrskaya Spit (western Kamchatka) using the measurement data taken in 2010–2011. Two indices describing the storm structure are used: the ratio of the attenuation stage duration to the total storm duration R_t and the ratio of the median value of storm wave height during the attenuation stage to the peak wave height of the storm event R_Hs. The variations in $R_t$ and $R_{Hs}$ during a year are statistically analyzed based on the ERA5 long-term wave reanalysis data. It is found that the $R_t$ index does not tend to change on a seasonal scale. When the $R_{Hs}$ index is close to one and changes slightly during a year, the coastal profile does not experience seasonal changes. If $R_{Hs}$ changes in course of a year decreasing significantly during the period of more intense waves, the coast experiences seasonal changes.

Conclusions. The variations in wave intensity during a year do not always result in the change of average position of the coastal profile. The key factor may consist in the seasonal trends in wave parameter changes within a storm cycle. The proposed index $R_{Hs}$ can be regarded as a criterion for the behavior type of sandy coasts on a seasonal scale.

Purpose. The purpose of the work is to estimate the long-term variations in concentration and flux of nutrients (inorganic nitrogen and inorganic phosphorus) in atmospheric deposition in Sevastopol.

Methods and Results. During 2015–2023, the samples of atmospheric deposition in Sevastopol were collected to analyze the concentration of dissolved forms of inorganic nitrogen (nitrate, nitrite and ammonium) and phosphorus. For each precipitation event, two types of samplers were used – the open and wet-only ones. Laboratory analysis of the collected samples was carried out in FSBSI FRC “Marine Hydrophysical Institute”. A total of 1264 samples of atmospheric deposition were analyzed. The maximum content of nutrients was determined in the samples with minimum precipitation amount, or after a long dry period. The Concentrations of inorganic forms of nitrogen from the open sampler were 1.3 times higher than those from the wet-only one. The phosphorus content in the open sampler exceeded that in the wet-only one by 3 times. The increased concentrations of ammonium in atmospheric deposition were revealed in spring, while those of nitrates – in fall-winter. The phosphorus flux in the samples from the open sampler reached its maximum value in autumn and exceeded the winter flux by 2.3 times.

Conclusions. The long-term variation in inorganic nitrogen flux is of a quasi-periodic pattern: its maximum flux was observed in 2017, and the minimum one – in 2019–2020. The maximum phosphorus flux in the samples from the wet-only sampler was noted in 2017–2018, whereas the phosphorus flux in the samples from the open sampler in 2021–2022 exceeded the flux in 2017–2018 by 1.5 times. As for inorganic nitrogen, its annual contribution to atmospheric deposition amounted 9.4–11.5 % of a river runoff, and as for phosphorus – 16.7–55.6 %. During the low-water period, these values were 12–14 % and 20–65 %, respectively.

Purpose. The work is purposed at studying the characteristics of shear flows induced by internal waves on the northeastern shelf of Sakhalin Island based on the results of numerical modeling of the transformation of barotropic tide along the selected two-dimensional (vertical plane) sections.

Methods and Results. The data from the WOA18 climate atlas with the 0.25° resolution for a summer season, and the bathymetry from GEBCO_2014 with the 1 min resolution are used to initiate a numerical model of the hydrodynamics of inviscid incompressible stratified fluid in the Boussinesq approximation. A tidal forcing from TOPEX/Poseidon Global Tidal Model (TPXO8) which is based on satellite altimetry data is preset at the deep-sea boundary. For the near-bottom and near-surface velocities (at the fixed depths: 15 m above the bottom and 15 m below the surface), the diagrams of probability of exceeding their levels are constructed both allowing for the direction (sign) and according to the absolute value. Then the velocities at a probability level 0.05, 0.1 and 0.15 are identified, and conversely, the probability with which the velocity 0.25 or 0.3 m/s would be exceeded is determined. The maps are constructed based on the obtained values.

Conclusions. It is shown that the studied shear flows are nonlinear and characterized by significant asymmetry in distribution both in direction (from coast/to coast) and over depth (in the near-bottom and near-surface layers). In the areas where the sea depth is 700–800 m, there is a clearly defined zone where the absolute values of near-surface velocities are several times higher than those of the near-bottom ones. The main zones including the local maxima of velocity field are located in the north – from Cape Elizabeth to Piltun Bay, with one more from Cape Bellingshausen to Cape Terpeniya.

Purpose. The study is purposed at identifying the variability features of the Angstrom parameter values obtained at the Black Sea stations Sevastopol and Section_7 of the AERONET network from spring, 2019 to spring, 2024 based on the satellite and ground monitoring data, as well as the results of atmospheric dynamics modeling.

Methods and Results. Comparative analysis and assessment of the Angstrom parameter values involved application of the following information on atmospheric aerosol: the data of ground-based measurements derived by a portable SPM photometer, the photometer at the stations of the AERONET international aerosol monitoring network, the VIIRS radiometer platform from the Suomi NPP satellite, the data on concentrations of suspended particles of PM2.5 and PM10 resulted from the Espada M3 detector measurements, as well as the results of atmosphere dynamics modeling (data of the HYSPLIT and SILAM models). The comparative analysis made it possible to reveal the dates on which the optical characteristics corresponding to dust aerosol were recorded at one of two indicated stations in the Black Sea, whereas at the other one, no aerosol of this type (i.e. optical characteristics corresponded to a clean atmosphere) was detected. This fact confirms the different aerosol loading in the atmosphere over the western and central parts of the Black Sea, and also the spatial variability of aerosol basic optical characteristics during dust transport from the Sahara Desert. The measurements of the PM2.5 and PM10 particle concentrations performed on the days with the background optical characteristics of atmospheric aerosol permitted to obtain the values of background characteristics of suspended particles: PM2.5 = 7 μg/m³ and PM10 = 8 μg/m³).

Conclusions. Low values of the Angstrom parameter (less than 0.8) do not by themselves indicate the presence of an aerosol, such as dust or smoke, in the atmosphere. However, being combined with high (exceeding the background values by more than 1.5 times) values of aerosol optical thickness and concentrations of PM2.5 and PM10 particles (exceeding the background values by more than 3 times), the data set is an evidence of the presence of aerosol – dust or smoke – in the atmosphere. It is noted that the aerosols of such types can be detected by the measurements of PM2.5 and PM10 particle concentrations only when they are in the atmosphere surface layer. Therefore, the conclusions on presence of these types of aerosols in the atmosphere, being based only on the measurements of calculated concentrations, are not reliable.