This study explores the potential for the penetration of technical waters from the Fukushima nuclear power plant (Fukushima NPP) into the fishing areas of Russia. Using a Lagrangian approach, which examines the advection of a large number of passive markers simulating waters released from the Fukushima NPP, the typical transport pathways to the South Kuril Islands are investigated, and an estimate of the time of such transport is provided. Calculations are conducted using satellite-derived and modelled velocity fields for the test year from August 24, 2022, to August 24, 2023. This study focuses on the advection of Lagrangian markers and highlights the potential for the rapid arrival of them from the Fukushima NPP into the southern Kuril region. This article emphasizes the importance of considering the seasonal variability in Kuroshio meandering and the impact of local mesoscale vortex advection related to the propagation of Lagrangian markers from the Fukushima NPP.

This paper presents a novel Lagrangian algorithm, the Lagrangian Eddy Boundary Delineation Algorithm (LEBDA), designed for determining the horizontal boundaries of mesoscale quasi-stationary eddies. In contrast to traditional Eulerian methods employed for similar tasks, LEBDA minimizes abrupt boundary changes, a critical advantage particularly relevant for the analysis of long-lived structures. A key feature of the algorithm is the use of passive tracer trajectories to construct R-contours, enabling accurate identification of both the eddy core and its periphery, while effectively filtering out transient perturbations. A comparison with the Automated Mesoscale Eddy Detection Algorithm (AMEDA), using the Lofoten Vortex as a case study, demonstrated that LEBDA provides a more physically consistent and temporally smooth delineation of the eddy boundary. Unlike AMEDA, which tends to overestimate eddy sizes (by up to 1.5 times), LEBDA exhibits a gradual and realistic evolution of boundaries. Analysis of the Lofoten Vortex parameters using LEBDA revealed a relationship between lobe formation, perimeter variations, interaction with the surrounding flow, and the influence of convection on the eddy's shape and stability.

This work presents a combined analysis of the spatial distributions of oceanographic fields based on Eulerian and Lagrangian approaches. In the Eulerian approach, the fluid motion is considered as a function of coordinates and time, and the equations of motion are formulated for specific points in space. In contrast, the Lagrangian approach focuses on tracking individual particles in the ocean, representing water masses or other materials, as separate objects moving according to the equations of motion. The variability of oceanographic characteristics in the Northwest Pacific region is examined, specifically analyzing the spatial distributions of oceanographic fields on October 24, 2010. The AMEDA algorithm is used to identify mesoscale eddies. Within the Eulerian approach, it is shown that regions prohibiting the stretching of mesoscale eddies only partially correspond to areas where large-scale eddies are located. Vortical structures and elements of large-scale circulation are well manifested in the distributions of the Lyapunov exponent (Λ-maps) and maps characterizing the trajectories of advected particles (S-maps). Enhanced values of kinetic and available potential energy correspond to the main circulation structures in the region. However, for analyzing the evolution of circulation structures, they are less informative compared to Λ-maps and S-maps, which accumulate information from the previous period. Spatial distributions of relative and potential vorticity are constructed. Positive values of relative vorticity outline the Kuroshio current from the north, while negative values outline it from the south, which is typical of jet currents with a pronounced zonal component. Mesoscale eddies exhibit elevated values of vorticity and a shielding effect (shielded vortices). In the Lagrangian experiment with passive tracer patches, it is demonstrated that the most deformation-resistant patch spent most of the analyzed time interval in a domain where the stretching of eddies is prohibited.

A new study is presented on the transport of markers (virtual particles) at the periphery of a quasi-stationary anticyclonic Lofoten vortex using R-contours calculated with the Lagrangian eddy boundary delineation algorithm (LEBDA) and archiving, validation and interpretation of Satellite Oceanographic data geostrophic velocities. It is shown that LEBDA has advantages over classical Eulerian approaches (e.g., automated mesoscale eddy detection algorithm): it minimizes abrupt changes in the eddy boundaries and reliably identifies the formation and evolution of lobes, which play a key role in the exchange of matter between the eddy and the surrounding flow. The obtained maps of marker escape times from the eddy and the number of rotations demonstrate spatial-azimuthal heterogeneity: some particles are retained for more than 180 days, while others leave the eddy quickly, confirming the existence of a coherent core and “sticky” zones at the boundaries. Verification using a drifter trajectory confirms the real nature of the identified processes of capture, retention, and escape of the markers from the vortex. Analysis of the escape-function and escape-fractal graphs reveals that markers leave the eddy in portions. Each such portion is reflected on the graphs as U-shaped and step-like structures. The partitioned (or intermittent) release of particles, as well as the dependence of the exit time on the initial position, indicates a fractal structure in the escape paths of markers from the vortex and suggests that chaotic advection is the dominant mechanism of water exchange between the eddy and the ambient flow.