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An analysis of water exchange between the Bering (Pacific Ocean) and Chukchi (Arctic Ocean) seas in the summer was carried out using satellite data on sea level, geostrophic currents, and measurement data of water transport in the Bering Strait. It is shown that there is good agreement (r = 0.85, July–October 1997−2019) between the velocities of geostrophic currents (satellite data) and measurements of water transport (buoy station data) through the Bering Strait. It has been established that the temporal variability of water transport through the Bering Strait is determined by sea level variations in the southern part of the Chukchi Sea (66°–68° N, 170°–172° W). Strengthening of the eastern (western) winds is accompanied by a decrease (increase) in the sea level in the southern part of the Chukchi Sea and, as a result, an increase (decrease) in the flow of water through the Bering Strait. An increase (decrease) in the flow of the Yukon River is accompanied by a rise (decrease) in sea level and changes in water circulation in the northern Bering Sea and the southern Chukchi Sea. [ABSTRACT FROM AUTHOR]

The spatial distribution and seasonal variability of mesoscale eddies in the Sea of Japan have been investigated based on the regional database created from the AVISO Mesoscale Eddies Trajectory Atlas (1993–2020). The database contains information about the trajectories and parameters of mesoscale eddies in the Sea of Japan. The eddy detection method is based on the analysis of altimetric maps of absolute dynamic topography. A total of 578 eddies with a lifetime of more than 90 days have been identified (273 anticyclonic and 305 cyclonic). The average lifetime of eddies is 202 days for anticyclonic and 143 days for cyclonic and mean radius of 58 km for anticyclonic and 61 km for cyclonic. The mean speed of anticyclones and cyclones along their trajectories is 2.8 and 3.7 cm/s; the mean orbital velocities of geostrophic currents are 19.0 and 15.1 cm/s, respectively. The maximum number of cases of formation and destruction of anticyclones falls in July–September during the period with high values of water inflow through the Korea Strait. Most of the cyclonic eddies are generated between January and June and decay during the cold half of the year (October–March). A joint analysis of maps of the mean surface circulation in the Sea of Japan (satellite altimetry data) and the spatial distribution of mesoscale eddy shows that the stable eddies of the Sea of Japan are associated with the quasi-stationary meanders of the East Korea East Korea Warm Curent, Subpolar Front, and Tsushima current. The position of meanders is mainly determined by the interaction of the currents with the bottom topography. [ABSTRACT FROM AUTHOR]

An analysis is made of unstable perturbations of a geostrophic current of finite transverse scale with a vertical parabolic velocity profile of a general form (with linear and constant velocity shear) in a vertically bounded layer. The model is based on the potential vortex equation in the quasi-geostrophic approximation taking into account the vertical diffusion of momentum and mass. The equation and boundary conditions are reduced to a spectral eigenvalue problem of the Orr–Sommerfeld type. To search for eigenfunctions and eigenvalues, a high-precision analytic–numerical method was used. Particular attention is paid to the study of unstable perturbations with a phase velocity exceeding the maximum flow velocity. Such instability should be distinguished from baroclinic instability and critical layer instability. It is found that the indicated instability can develop in ocean currents when the problem parameters vary in a wide range of values. It is also obtained that, at an increase in the Prandtl number, the phase velocity of such perturbations increases and can significantly exceed the maximum flow velocity. However, the occurrence of such unstable perturbations is possible only when the maximum flow velocity is located in the inner region of the layer (but not necessarily in its center). It has also been found that narrow currents (the transverse scale is equal to or smaller than the Rossby radius) with a parabolic vertical profile can be unstable. The most unstable perturbations have approximately equal scales along and across the flow; that is, they are circular perturbations. A discussion of various types of geostrophic current instability with a vertical parabolic velocity profile as applied to the ocean is presented. [ABSTRACT FROM AUTHOR]

The trajectories of 114 000 passive particles regularly distributed on a grid in the Sea of Okhotsk are calculated for each day of the interval from January 31, 1997 to March 10, 2021, based on satellite altimetry data on geostrophic current speeds. All particles coming to the Sea of Okhotsk from the Pacific Ocean are identified and the age of the Pacific-origin waters and the area where these waters enter the sea are determined. Using daily vessel-position data in the walleye pollock fishery from 1997 to 2021, Lagrangian maps of the origin and age of the Pacific waters over the same period, and statistical analysis, it is shown that the Walleye pollock fishing grounds are more often in the Pacific waters which passed through the northern Kuril Straits not more than 100 days before the catch dates than in the waters which entered the sea to the south or have been in the sea for more than 100 days. Analysis of satellite imagery of sea surface temperatures leads to the conclusion that the reasons for the aggregation of walleye pollock catch locations in intrusions and Lagrangian fronts of Pacific waters are their warmer temperatures and higher concentrations of feed. [ABSTRACT FROM AUTHOR]

The distribution of fresh water in the East Siberian Sea (ESS) and Laptev Sea (LS) in the period of the least ice coverage (August–October) has been analyzed using satellite data on sea level and CTD data from ship observations. It is shown that there is a good agreement between the salinity/density distribution in the surface water layer and the sea level in the study area. An increase (decrease) in the runoff of the Lena River during the summer flood leads to an increase (decrease) in the sea level in the eastern part of the LS and in the western and southwestern parts of the ESS in September and October (r = 0.52–0.59 in 1993–2019). The intensification of the western winds is accompanied by a decrease in salinity and a rise in sea level in the coastal areas of the LS and ESS. Eastern winds cause a decrease in sea level in the southern regions of the LS and ESS and the flow of waters with low salinity from the coastal to the open part of the sea. Western/eastern winds are accompanied by eastern/western directed geostrophic currents in the region of the Sannikov Strait and in the southwestern part of the ESS. [ABSTRACT FROM AUTHOR]

The Soya Current is formed from the transformed subtropical waters of the Tsushima Current, which flows from the Sea of Japan through the La Perouse Strait, spreads along the northern coast of Hokkaido, and enters the Pacific Ocean through the Yekaterina and Kunashir straits. An analysis of satellite data (1993–2019) on sea level, geostrophic current velocity, surface water temperature, and chlorophyll concentration in the southern part of the Sea of Okhotsk, in the zone of the La Perouse Strait (Sea of Japan), and in the southern Kuril region of the Pacific Ocean has been carried out. It has been established that an increase in the sea level difference between the Sea of Japan and the Pacific Ocean leads to the intensification of the Soya current. The main contribution to the change in the level difference between the Pacific Ocean and the Sea of Japan in autumn belongs to anticyclonic eddies and meanders of the Subarctic Front in the Pacific Ocean. An increase (decrease) in the penetration of transformed subtropical waters through the La Perouse Strait is accompanied by an increase (decrease) in the temperature of the surface water layer in the southern part of the Sea of Okhotsk (r = 0.67 in 2000–2019) and a decrease (increase) in the chlorophyll concentration in the Kuril region of the Pacific Ocean (r = –0.70 in 1998–2019) in September–October. [ABSTRACT FROM AUTHOR]

The dynamics of mesoscale eddies in the Bering Sea is studied by the method for automated eddy identification on the basis of altimetry-derived sea-level anomaly fields (SLA method, AVISO+). For this purpose, a regional database has been created for the Bering Sea (1993–2018) on the basis of the "Mesoscale Eddy Trajectory Atlas Product" global dataset to estimate the polarity (cyclonic/anticyclonic), distribution, radius, intensity, nonlinearity, velocity, and motion trajectories of eddies and determine regions of their formation and decay. The results confirm that mesoscale eddies play a significant role in the Bering Sea. About 592 eddies with a minimum lifetime of 90 days were identified (361 anticyclonic and 231 cyclonic). Anticyclonic and cyclonic eddies had average radii of 53.2 and 63.5 km in the Bering Sea. The average orbital velocities of geostrophic currents in the outer closed loops of the eddies were 14.0 and 10.8 cm/s, respectively. The mean speed of anticyclones and cyclones along their trajectories was 5.1 and 6.2 cm/s. Most of the mesoscale eddies were associated with currents of the Bering Sea. This shows that eddies are mainly generated due to baroclinic/barotropic instability of the Bering Sea slope and Kamchatka currents. The eddy generation in the North Aleutian slope current should be influenced by water exchange through the straits of the Aleutian ridge. The number of "new" anticyclonic eddies is maximum in April–July. Most of the cyclonic eddies are generated in the cold half of the year (January–March). Seasonal variability of the Bering Sea circulation affects the intensity of eddy generation. [ABSTRACT FROM AUTHOR]

An analysis of satellite data and Argo float data has shown the variability in the sea surface temperature (SST), sea level, and geostrophic currents in the northwestern Pacific Ocean and southwestern Bering Sea caused by the nodal tide with a period of 18.6 years. It is found that an increase in the nodal tide amplitude leads to a sea-level decrease and the formation of cyclonic water circulation in the Blizhniy Strait area. In the Bering Sea, there is no water flow directed northward from the Blizhniy Strait to the mainland coast. In the northwestern part of the Pacific Ocean, the westward flow of waters of the Alaskan Stream weakens and a cyclonic eddy is formed. The sea-level decrease is caused by an increase in salinity/density of water in the 50–400 m layer due to increased tidal mixing in the Aleutian Straits and the Blizhniy Strait. Tidal amplification (attenuation) was accompanied by a decrease (increase) in SST in the northwestern Pacific Ocean and southwestern Bering Sea. [ABSTRACT FROM AUTHOR]

AVISO satellite data on the speeds of geostrophic currents from 2004 to 2018 are used to associate a substantial reduction in the saury catch in recent years with a change in the oceanographic situation in the Russian fishing grounds off the coast of the southern and middle Kuril Islands and Hokkaido Island. Lagrangian maps of the origin of water masses, calculated for this period of time on the basis of the AVISO field, and with overlaid positions of fishing vessels of Russia, Japan and Korea, show that this catastrophic reduction is due to a change in the pathways of the nutrient-rich subarctic waters of the Oyashio current in recent years. The greatest changes in the hydrological regime since 2015 were caused by intensification of the third branch of the Oyashio, which transports the waters of this current to the open ocean. At the same time, traditional fishing grounds off the eastern coasts of Hokkaido and southern Kurils have been reduced, while good fishing grounds have appeared in the open ocean. [ABSTRACT FROM AUTHOR]

A study of water circulation in the northwestern part of the Bering Sea using AVISO satellite data on velocities of geostrophic currents from 2002 to 2017 showed a significantly variable dynamics of the surface waters. In January, the main current of the surface waters is directed toward the southwest along the continental slope in contrast to anticyclone water circulation in shelf. In July, the surface water current is oriented to the northeast along the continental slope, whereas cyclonic water circulation is dominant at shelf. The formation of winter mesoscale anticyclones is caused by a gain of low-temperature and low-saline shelf waters. The temporal variability of direction and velocity of summer currents is related to coastal upwelling, which is caused by the southern winds over the western part of the Bering Sea. The presence of upwelling and eddies should be considered one of the factors leading to the formation of an area with high chlorophyll concentration close to the coast during summer. [ABSTRACT FROM AUTHOR]

A spectral problem of the Orr–Sommerfeld type is considered to describe unstable disturbances of oceanic geostrophic currents with a linear vertical velocity profile by taking into account the vertical diffusion of buoyancy and friction. Numerical solutions are obtained for different values of the dimensionless parameters of the problem. Calculations of the spectra of eigenvalues and growth rates are compared with those of a similar problem for an ideal fluid. It is shown that (a) dissipation expands the range of wave numbers of unstable disturbances, (b) dissipation can increase the growth rates of baroclinic disturbances, (c) disturbances driven by the instability of the critical layer can grow faster than baroclinic disturbances, and (d) currents with a width equal to or less than the Rossby radius can be unstable; nearly circular (axisymmetric) unstable disturbances (submesoscale eddies) can develop in narrow currents or frontal zones. [ABSTRACT FROM AUTHOR]

Abstract—A spectral problem of the Orr–Sommerfeld type for describing stable and unstable perturbations of oceanic geostrophic flows with linear vertical velocity shear is considered (parabolic vertical velocity profile). Calculations of eigenvalues, increments of growth rate of unstable modes, and eigenfunctions of the fastest growing perturbations are presented. It is found that the instability of the geostrophic flow is observed over a wide range of horizontal scales: in addition to longwave perturbations with a phase velocity exceeding the maximum velocity of the geostrophic current and perturbations with the scales of the Rossby radius, shortwave modes exist with scales much smaller than the Rossby radius (submesoscale structures). The results of the model are used to describe intrusions in the Arctic basin, which are observed under conditions of absolutely stable stratification. [ABSTRACT FROM AUTHOR]

Abstract: Sea level measurements from an absolute dynamic typography dataset for the period of 1993-2015 were used to study the variability in geostrophic circulation in the Labrador and Irminger seas. Analysis of current intensity trends calculated by geostrophic formulas has shown a weakening in cyclonic circulation observed in these two convection centers. The intensity trends are negative in all the main currents making up the Subpolar Gyre: the Labrador, East Greenland, West Greenland, and Irminger currents. On average, the negative intensity trends in the indicated currents are -0.3 cm s-1 yr-1, in individual areas reaching -0.5 cm s-1 yr-1, which corresponds to a decrease in current speed of 6.9-11.5 cm/s for the 23-year interval. Weakening of cyclonic circulation is likely predetermined by weakening convection processes and a decrease in the dome-shaped curvature of isopycnal surfaces generated by upwelling of weakly stratified water closer to the surface. This is confirmed by analysis of satellite data: in periods when deep convection weakens, the intensity of cyclonic circulation decreases at the margin of the Labrador and Irminger seas. Simultaneously with weakening currents, an increase in intensity is observed from the outer (with respect to the convection centers) margin of the considered currents, including in coastal zones. [ABSTRACT FROM AUTHOR]

The instability of long-wave disturbances of a geostrophic current with linear velocity shear is studied with allowance for the diffusion of buoyancy. A detailed derivation of the model problem in dimensionless variables is presented, which is used for analyzing the dynamics of disturbances in a vertically bounded layer and for describing the formation of large-scale intrusions in the Arctic basin. The problem is solved numerically based on a high-precision method developed for solving fourth-order differential equations. It is established that there is an eigenvalue in the spectrum of eigenvalues that corresponds to unstable (growing with time) disturbances, which are characterized by a phase velocity exceeding the maximum velocity of the geostrophic flow. A discussion is presented to explain some features of the instability. [ABSTRACT FROM AUTHOR]

The linear theory of long waves was applied to study horizontal motions of the water layer in a rotating ocean which appear after tsunami generation by an earthquake. The structures of residual potential and eddy fields are analyzed on the basis of the analytical solution of a model axisymmetric problem for an ocean of constant depth. The estimates of the horizontal displacements of water particles, velocity of the eddy current, and energy of the geostrophic eddy are calculated for typical conditions of the tsunami source. Particular features of the residual fields related to the existence of stable stratification are considered. Static and dynamic numerical models are described that allow us to calculate the residual potential field and its evolution related to the realistic events. The field of residual horizontal displacements of water particles for the catastrophic earthquake near the coasts of Japan on March 11, 2011, is calculated and analyzed. [ABSTRACT FROM AUTHOR]

A quasi-geostrophic contour dynamics model permitting one to study flows induced by a system of vortex patches in a two-layer ocean with round shore boundaries in the presence of specified background flows caused by the bottom relief, the β effect, and sources and sinks at the boundaries is proposed. The principal relations of the model are presented and the algorithm of its numerical realization is described. Some experimental results of the study of the evolution of unstable two-layer vortices are demonstrated. [ABSTRACT FROM AUTHOR]

Cyclone-anticyclone asymmetry in a rotating fluid results in vortices with cyclonic rotation being attenuated more rapidly than vortices with anticyclonic rotation due to the Ekman bottom friction. To explain this effect, some authors invoked rather complex integral (averaged along the vertical) models with the parametrization of nonlinear friction. A simple analytical model, free of the procedure of formal averaging and based on a separate consideration of the equations for external flow in the nonviscous region and internal flow in the boundary layer, is investigated in this work. The corresponding equations are written in the so-called geostrophic momentum approximation, which makes it possible to take into account the nonlinear advective mass transport in the boundary layer at small Rossby numbers. The nonlinear equation of the hyperbolic type for the tangential velocity, which describes the process of attenuation of an axisymmetric vortex, is obtained from the condition of total mass conservation. Based on the solutions to this equation, it was shown that distinctions in the character of vortex attenuation are caused by deviations from the geostrophic regime in the nonviscous region. It was established that the concentration (compression) of anticyclonic vortices and the extension of cyclonic ones take place in the process of attenuation. [ABSTRACT FROM AUTHOR]