Vol 23, No 3 (2023)

The main motivation of this research is to assess the trends of storm recurrence for the time period from 1979 up to 2020 and to analyze the connection between storminess and large-scale atmospheric circulation indices. This research contains information about the number of storms that occurred in seven Russian Seas, including the Black, Caspian, Barents, Kara, Bering Seas, the Sea of Okhotsk and the Sea of Japan/East Sea. The analysis of wave climate and storm activity is based on the results of wave modeling by WAVEWATCH III with input NCEP/CFSR wind and ice data. The long-term significant wave height (SWH) maximum is 15.5 m in the Sea of Okhotsk and 16.5 m in the Bering Sea. Significant linear basin-wide positive trends in the number of storms were found in the Kara, Caspian, Bering, Okhotsk Seas, and in the Sea of Japan. The weak positive correlation was found only between the number of storms and North Pacific index in the Bering Sea and between the number of storms and Arctic oscillation index in the Barents Sea. For other seas, it is no connections between number of storms and large-scale atmospheric indices, therefore, storm activity in the inner and semi-closed seas is regulated by the local wind and ice conditions, basin orography and bathymetry.

The Norwegian Sea is the meeting place of warm and salty Atlantic waters with cold and fresh Arctic waters. The thermal and haline frontal zones (FZs) formed as a result of this interaction are areas of increased horizontal gradients of physical, chemical, and biological parameters, and have a significant impact on regional circulation. Many mesoscale eddies are generated in the FZs which are actively involved in the eddy dynamics of the Norwegian Sea. The aim of this work is to analyze the spatio-temporal variability of the vertical structure of FZs in the Norwegian Sea, as well as the eddies that form within their boundaries. The work uses data from the oceanic reanalysis GLORYS12V1, as well as the Atlas of Mesoscale Eddies “Mesoscale Eddy Trajectory Atlas product META 3.2 DT” for the period 1993–2021. We analyze the average depth and thickness of FZs, the vertical distribution of their thermohaline gradients and areas. The work examines the seasonal and interannual variability of the volumes of thermal and haline FZs, the seasonal and interannual variability of mesoscale eddies, their spatial distribution, trajectories, and main parameters. In some areas, deepening of FZs has been established, and their thickness can reach 900 m. The presence of significant haline gradients in the layer of 250–750 m has been found, while thermal FZs can be traced vertically up to 1000 m compared with haline FZs. In some FZs, the interannual variability may exceed the seasonal one. The greatest variability of haline FZs can be traced in the autumn period, and the smallest – in the winter–spring. It is noticeable in the summer period that thermal FZs weaken. Eddies can leave the boundaries of the FZs and move away from the place of origin for hundreds of kilometers. The number and lifetime of cyclones exceed similar estimates for anticyclones, while anticyclones travel long distances compared to cyclones.

The Atlantic Water is the main source of heat and salt in the Arctic. Properties of the Atlantic Water inflow regionally affect sea ice extent and deep water formation rate. The Atlantic Water heat transported into the Nordic Seas has a significant impact on the local climate and is investigated here along with its inter-annual variability. We use the ARMOR3D dataset, which is a collection of 3D monthly temperature, salinity and geostrophic velocities fields, derived from in situ and satellite data on a regular grid available since 1993. We compare the heat transport across seven zonal transects in the eastern part of the Nordic seas, from the Svinøy section (65◦N) to the Fram Strait (78.8◦N). The correlations of the interannual variations of the advective heat fluxes rapidly drop from Svinøy to Jan Mayen sections and between Bear Island and Sørkapp sections. This is a result of different tendencies in its interannual evolution over the latest decades in the southern and the northern parts of the study region, as well as of a differential damping of the observed periodicities along the AtlanticWater path on its way north (the amplitude of 5–6 year oscillations drops significantly faster than that of 2–3 year oscillations). A certain link between the heat fluxes and the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and East Atlantic (EA) indices is observed only at the southern sections. On the other hand, the heat fluxes at all sections show a consistent increase during the dominance of western weather typeWand a decrease – of meridional weather type C. The link is explained by the variations of the wind fields, favorable for the sea-level build-up (Ekman pumping) east of the branching of the Norwegian Current for type W and an opposite tendency for type C.

The shores of the Kaliningrad Region (the Russian part of the South-Eastern Baltic Sea) are regularly exposed to extreme storms, which leads to intensive abrasion and flooding of the land. Based on archival data, meteorological monitoring, forecast and synoptic maps, an analysis of extreme storms observed in the autumn–winter periods of the early 21st century was done. The cyclone type was determined using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model), which makes it possible to reconstruct the trajectory of the approach of the atmospheric vortex to the coast. The seasons with clusters of storms were identified, when deep cyclones affected the coasts of the Kaliningrad Region in a relatively short time. Regardless of the type of trajectory, storms cause destruction of both natural and infrastructure objects. But the shores of the northern exposure are most susceptible to destruction by “diving” cyclones, the wave regime of which has a high potential energy. Earlier it was noted that the frequency of cyclones with northerly winds increases. Clusters of northern cyclones are especially dangerous, as was in January 2022, when 4 atmospheric eddies affected the coast with an interval of several hours to 2–3 days. When the water level was high, the waves crashed on the coast, causing catastrophic damage. The coastal monitoring revealed numerous destruction of the banks, breakthroughs of the foredune, both flooding and collapse of forests, critical damage to engineering and coastal protection structures and infrastructure facilities. Dozens of hectares of coastal territories have been lost. There are environmental problems associated with numerous emissions into the marine environment of a huge amount of anthropogenic mega-, macro-, meso-, micro-debris with a predominance of plastic after extreme storms.

The paper analyzes the decomposition of the initial seismic data by the methods of wave reversal in time when constructing seismic attributes. Within the framework of a formal approach to decomposition, as a mapping of data from one space into data of a larger dimension, a classification of existing seismic survey methods is given. Separation of the stage of decomposition in seismic data processing makes it possible to streamline the existing directions of research in this area of seismic exploration. The vector decomposition, which is the basis of a new method of seismic data processing Reverse Time Holography (RTH), is analyzed in detail. The RTH method includes, as a special case, the depth migration method, the offset reflection amplitude analysis method, the acoustic inversion method, and is an alternative to the migration-based velocity estimation method and the full wave inversion method. A close connection between the technique of wavefront time reversal in seismic exploration and analogous time reversal in optics and acoustics is noted. The variety of deep seismic attributes obtained in the RTH method based on vector decomposition makes it possible to solve a wide range of practical problems of prospecting and developing hydrocarbon deposits at a new qualitative level. The RTH method has been successfully tested at 21 hydrocarbon fields in various oil and gas provinces of the Russian Federation.

Geomagnetic storms have very profound effects on the Total Electron Content (TEC) of the ionosphere. In order to investigate the equatorial and low-latitude ionospheric response to the geomagnetic storms of varying intensities, a detailed study of vertical TEC (VTEC) variations resulting from Global Positioning System (GPS) data acquired at four GPS stations in Nepal along 80°–90° E longitude and 26°–30° N latitude sector has been carried out in the present work. The results were analyzed with other favorable inducing factors (solar wind parameters and geomagnetic indices) affecting TEC to constrain the causative factor. Positive phases are observed for all the storms studied. During the severe geomagnetic activity, the deviation was ~18 TECU, while it was recorded ~12 TECU and ~8 TECU during moderate and minor geomagnetic activity, respectively. The Detrended Cross-Correlation Analysis (DXA) illustrates that the value of the hourly average VTEC of the BESI station was found to have a strong positive correlation with other stations in all types of storm events, indicating a similar response of all stations towards the space weather events. In addition, the correlation of VTEC with solar wind parameters and geomagnetic indices illustrated that the VTEC shows a strong positive association with solar wind velocity (Vsw) in all three geomagnetic events. In contrast, the correlation of plasma density (Nsw), interplanetary magnetic field (IMF-Bz), the symmetric horizontal component of geomagnetic field (SYM-H), and Geomagnetic Auroral Electrojet (AE) index with VTEC vary with the intensity of the storm. Overall results of the study have revealed the characteristic features of TEC variation over Nepal regions during magnetic storms, which validates earlier research on ionospheric responses to geomagnetic storms and theoretical assumptions.