Vol 40, No 5 (2024)

Purpose. The purpose of this paper is to identify and study the cases of long-lasting steady winds of one direction over the Black Sea, and to analyze the accompanying conditions in the surface atmosphere and middle troposphere in winter (December – March).

Methods and Results. The situations with extremely long-lasting steady winds of persistent direction, namely when the prevailing wind over the sea does not change its direction for 5 days or more are considered. The analysis is based on the 6-hour data on wind speed at the 10 m height, the 500 hPa geopotential height and the surface pressure from the ERA5 reanalysis of the European Centre for Medium-Range Weather Forecasts for 1979–2021. Within the analyzed period, 10 cases of steady winds were identified. In most cases it was a north-eastern wind. At the same time there were 3 recorded cases of the eastern, northern and south-western winds. The empirical orthogonal function analysis performed for a set of steady wind cases shows that distribution of the first modes of the geopotential height and surface pressure fields has a spatial structure with a stable high-pressure area over the European territory. The contribution of these modes to the total variability is 65 and 47%, respectively. Analysis of the revealed situations with steady winds shows that in all the cases with northern and north-eastern winds, atmospheric blocking in a form of a quasi-stationary anticyclone was observed in the middle atmosphere over the Northern Europe/Scandinavian Peninsula. In the case of northern wind, an extensive high-altitude anticyclone was located over the northern part of the European Russia. The values of the Tibaldi and Molteni blocking index confirm the fact that the considered cases of long-lasting north-eastern and northern winds correspond to the blocking conditions over the European region. A steady eastern wind was observed when the extensive anticyclone in the middle troposphere was actively moving from the north of the Scandinavian Peninsula to the south-east. In the case of a long-lasting south-western wind, a subtropical high-pressure ridge as well as an intense western transfer in the European region took place in the middle troposphere that generated a steady wind over the Black Sea.

Conclusions. The analysis results indicate that the considered cases with steady north-eastern and northern winds over the Black Sea are related to the blocking processes in the atmosphere of the European region.

Purpose. The work is purposed at analyzing the regional characteristics of ice accretion frequency and meteorological conditions of vessel icing in the Barents Sea region, as well as long-term trends of these characteristics observed in the context of modern climate change.

Methods and Results. The results of studying the frequency of ice accretions are obtained by statistical processing of 3-hour observations at a network of weather stations located near the coast and on the islands of the Barents Sea for the period 1966–2022. The frequency of vessel icing is estimated using the D. Overland method which is based on calculating the spray icing intensity involving the data on wind speed, air temperature, sea water temperature, and its freezing point. The ERA5 reanalysis for 1979–2022 is used as the input data for the D. Overland method. The average annual number of days with the atmospheric phenomena during which dangerous ice accretions of different types can be formed, is obtained based on the observation data. The time trends in the average annual number of days with such phenomena are quantitatively evaluated. The reanalysis data processing has permitted to obtain the average annual number of days with vessel icing for the Barents Sea area. The regions of the highest frequency of extreme vessel icing are identified. The time trends in frequency of the changes in a number of days with vessel icing of different intensity are considered for the period 1979–2022.

Conclusions. On the Barents Sea coast, on average about three days per year with dangerous ice accretions of different types are observed. From 1966 to 2022, every 10 years the number of such phenomena decreased on average by 0.58 days. The highest frequency of marine icing is revealed in the eastern part of the Barents Sea and near the western coast of Novaya Zemlya where the average number of days with extreme icing exceeds 30 days per year. In course of the period 1979–2022, both a decrease in the average annual number of days with icing up to three ones per year (south of 75° N and west of 50° E) and their increase up to three days per year (in the northern and eastern parts of the Barents Sea) were observed.

Purpose. The purpose of the study is to identify the features of spatial and vertical distribution of hydrocarbons in bottom sediments of the coastal area under constant anthropogenic load, and to assess the likely sources of their inlet into the marine environment (using Kamyshovaya Bay as an example).

Methods and Results. The surface layer of bottom sediments (nine stations) and the sediment column were sampled in July 2021 as a part of long-term monitoring of the Sevastopol bays jointly performed by FRC IBSS and FRC MHI. The features of spatial distribution of hydrocarbons, alkanes and some geochemical markers in the surface layer (0–5 cm) and the vertical profile of bottom sediments are studied. The 30-year accumulation history of the considered substances in the bay bottom sediments is analyzed. The concentration of hydrocarbons in the bottom sediments ranges from 27.6 to 98.5 mg/kg that allows us to classify these sediments as low-polluted. A layer-by-layer study of the hydrocarbon composition in the bay bottom sediments shows that in course of 30 years the bottom sediments were not significantly polluted with hydrocarbons. The results of analyzing the alkane composition and the geochemical marker values make it possible to establish that, as well as in the surface layer, the predominant source of hydrocarbon inlet was allochthonous and autochthonous organic matter. The increased values of geochemical markers identifying oil pollution indicate the fact that the inlet of oil and oil products can be considered a secondary source of hydrocarbons.  

Conclusions. Hydrocarbons in the bottom sediments are distributed unevenly over the Kamyshovaya Bay water area, namely in the central part of the bay, a zone of the increased pollution is formed. It can be a consequence of the processes taking place in the semi-enclosed bay, as well as conditioned by the type of bottom sediments. The results of studying the hydrocarbon composition of bottom sediments show that in course of the past 30 years and up to present, Kamyshovaya Bay has been under the anthropogenic load which fluctuated insignificantly due to the degree of economic activity of the port. At that the level of the bay pollution remains low.

Purpose. The purpose of the work consists in performing a comparative numerical simulation of generation and propagation of tsunami waves induced by the M = 7.6 earthquake on January 1, 2024 on the Noto Peninsula, Ishikawa Prefecture, Japan.

Methods and Results. Four different variants of a seismic source are simulated within the framework of the earthquake source keyboard mechanism. A multi-block source is considered, in which, while modeling the earthquake, a sequential motion of key-blocks was specified. It is shown that the dynamics of this process in a seismic source will determine the formation of corresponding tsunami source and wave fronts propagating from this source, and that the shape of earthquake source significantly affects the values of maximum wave heights in the water area. Applying the information from the tide-gauge stations in the Sea of Japan, and the Tsugaru and Tatar straits permits to compare the real records of maximum values of the tsunami wave amplitudes at these stations and the computed tide-gauge ones resulted from numerical modeling of different dynamics of keyboard blocks in the seismic source.

Conclusions. It is shown that using the keyboard model of earthquakes, one can adequately simulate even such complex earthquake sources as the one that occurred in the northwest of the Noto Peninsula and on the western coast of Honshu Island where, besides a great number of settlements, the largest Japanese operating nuclear power plants are located.

Purpose. The work is aimed at studying the hydrodynamic conditions of formation of the sand spits in Taganrog Bay of the Azov Sea from the viewpoint of the morphological features of spits.

Methods and Results. The analysis is based on the results of numerical modeling the hydrodynamic parameters of the entire Azov Sea over 42 years, from 1979 to 2020. The generated data array consists of the hourly spatial fields of bottom current velocities and directions, as well as the wind wave significant heights and directions of their propagation. A significant difference between the sand spit hydrodynamic regimes of the northern (Belosarayskaya and Krivaya spits) and southern (Ochakovskaya, Chumburskaya, Sazalnikskaya and Yeyskaya ones) coasts has been established.

Conclusions. In the coastal waters of the Belosarayskaya and Krivaya spits (the northern coast), the frequency of currents from the east prevails. The Beglitskaya (the northern coast), Ochakovskaya and Sazalnikskaya (the southern coast) spits are characterized by the predominance of currents from the west. In the region of the Belosarayskaya and Krivaya spits, the long-term mean velocities of the currents directed to the east are slightly higher than those of the currents directed to the west. In the areas of the Beglitskaya spit (the northern coast), as well as the Ochakovskaya, Chumburskaya, Sazalnikskaya and Yeyskaya spits in the southern part of the bay, the eastward directed currents dominate noticeably, both in terms of mean and maximum speeds. In the coastal waters of the Belosarayskaya and Krivaya spits, both the mean and maximum heights of the waves propagating to the east slightly exceed those of the waves propagating to the west. As for the Beglitskaya, Ochakovskaya, Chumburskaya, Sazalnikskaya and Yeyskaya spits, the dominating westward direction of wave propagation is, on average, a characteristic feature, whereas the waves of maximum heights develop during the eastern storms.

Purpose. The work is purposed at evaluating the errors in atmospheric correction of the satellite (MODIS Aqua, MODIS Terra, VIIRS SNPP, VIIRS JPSS, NASA HawkEye (SeaHawk) and OLCI (Sentinel-3A)) data for July 28–29, 2021 when a dust transport over the Black Sea region was recorded.

Methods and Results. To assess the scale and intensity of the studied dust transfer, the results of in situ photometric measurements and satellite data were analyzed. The in situ measurement data on aerosol optical depth (AOD) were obtained at the western Black Sea stations Galata_Platform and Section_7 of the AERONET network (AErosol RObotic NETwork). The variability of sea remote sensing reflectance values during the period under study was analyzed using the additional AERONET − Ocean Color (AERONET-OC) data. The color scanner (MODIS Aqua/Terra, VIIRS SNPP/JPSS, HawkEye and OLCI) measurements presented in the Ocean Color database were used as satellite data.

Conclusions. The approximation of errors in the atmospheric correction of satellite data for July 28–29, 2021 has resulted in obtaining the power-law dependencies close to l^-5. This is explained by the total contribution of molecular component (l^-4) and aerosol absorption (l^-1). On July 29, 2021, a better pronounced power function is observed since the dust aerosol concentration increases on this day, whereas the contribution of aerosol absorption becomes close to the power dependence l^-2. Also on the same day, the CALIPSO satellite data showed the presence of not only dust aerosol, but also the biomass burning over the region under study. Modeling the back trajectories of HYSPLIT air flows has shown that just on this day the aerosol masses moved towards the Black Sea from the southwest (Crete Island), that was additionally confirmed by high AOD values over the eastern Mediterranean Sea on July 29, 2021. The combination of two types of absorbing aerosols is assumed to induce even larger inaccuracies in determining the sea remote sensing reflectance for the period under study.