The impact of circulation features on the dispersion of radionuclides after the nuclear submarine accident in Chazhma Bay (Japan Sea) in 1985: A retrospective Lagrangian simulation.

A reactor accident on a nuclear submarine in Chazhma Bay (Peter the Great Bay (PGB), Japan Sea), occurred at 11:55 h local time on 10 August 1985 and caused radioactive contamination of sea water and air. The potential transport pathways of radioactive tracers on the sea surface and at different depths in the water during the month after the accident have been simulated based on the regional ocean modelling system (ROMS) with high resolution and Lagrangian analysis. The spread of radionuclides on the sea surface in the adjacent Ussuri Bay was strongly influenced by two typhoons, which mixed the polluted water in the bay and reduced the concentration of radionuclides in the fallen spot. The surface transport of tracers from the Chazhma and Strelok bays was also affected by multidirectional winds, whereas the dispersion of tracers in the deeper layers was influenced by eddies in PGB.

Mechanism of destruction of transport barriers in geophysical jets with Rossby waves.

The mechanism of destruction of a central transport barrier in a dynamical model of a geophysical zonal jet current in the ocean or the atmosphere with two propagating Rossby waves is studied. We develop a method for computing a central invariant curve which is an indicator of existence of the barrier. Breakdown of this curve under a variation in the Rossby wave amplitudes and onset of chaotic cross-jet transport happen due to specific resonances producing stochastic layers in the central jet. The main result is that there are resonances breaking the transport barrier at unexpectedly small values of the amplitudes that may have serious impact on mixing and transport in the ocean and the atmosphere. The effect can be found in laboratory experiments with azimuthal jets and Rossby waves in rotating tanks under specific values of the wave numbers that are predicted in the theory.

Detection of barriers to cross-jet Lagrangian transport and its destruction in a meandering flow.

Cross-jet transport of passive scalars in a kinematic model of the meandering laminar two-dimensional incompressible flow which is known to produce chaotic mixing is studied. We develop a method for detecting barriers to cross-jet transport in the phase space which is a physical space for our model. Using tools from the theory of nontwist maps, we construct a central invariant curve and compute its characteristics that may serve as good indicators of the existence of a central transport barrier, its strength, and topology. Computing fractal dimension, length, and winding number of that curve in the parameter space, we study in detail the change in its geometry and its destruction that is caused by local bifurcations and a global bifurcation known as reconnection of separatrices of resonances. Scenarios of reconnection are different for odd and even resonances. The central invariant curves with rational and irrational (noble) values of winding numbers are arranged into hierarchical series which are described in terms of continued fractions. Destruction of central transport barrier is illustrated for two ways in the parameter space: when moving along resonant bifurcation curves with rational values of the winding number and along curves with noble (irrational) values.

Effect of dynamical traps on chaotic transport in a meandering jet flow.

We continue our study of chaotic mixing and transport of passive particles in a simple model of a meandering jet flow [Prants et al., Chaos 16, 033117 (2006)]. In the present paper we study and phenomenologically explain a connection between dynamical, topological, and statistical properties of chaotic mixing and transport in the model flow in terms of dynamical traps, singular zones in the phase space where particles may spend an arbitrarily long but finite time [Zaslavsky, Phys. D 168-169, 292 (2002)]. The transport of passive particles is described in terms of lengths and durations of zonal flights which are events between two successive changes of sign of zonal velocity. Some peculiarities of the respective probability density functions for short flights are proven to be caused by the so-called rotational-island traps connected with the boundaries of resonant islands (including the vortex cores) filled with the particles moving in the same frame and the saddle traps connected with periodic saddle trajectories. Whereas, the statistics of long flights can be explained by the influence of the so-called ballistic-islands traps filled with the particles moving from a frame to frame.

Chaotic mixing and transport in a meandering jet flow.

Mixing and transport of passive particles are studied in a simple kinematic model of a meandering jet flow motivated by the problem of lateral mixing and transport in the Gulf Stream. We briefly discuss a model stream function, Hamiltonian advection equations, stationary points, and bifurcations. The phase portrait of the chosen model flow in the moving reference frame consists of a central eastward jet, chains of northern and southern circulations, and peripheral westward currents. Under a periodic perturbation of the meander's amplitude, the topology of the phase space is complicated by the presence of chaotic layers and chains of oscillatory and ballistic islands with sticky boundaries immersed into a stochastic sea. Typical chaotic trajectories of advected particles are shown to demonstrate a complicated behavior with long flights in both the directions of motion intermittent with trapping in the circulation cells being stuck to the boundaries of vortex cores and resonant islands. Transport is asymmetric in the sense that mixing between the circulations and the peripheral currents is, in general, different from mixing between the circulations and the jet. The transport properties are characterized by probability distribution functions (PDFs) of durations and lengths of flights. Both the PDFs exhibit at their tails power-law decay with different values of exponents.

Clustering in randomly driven Hamiltonian systems.

The motion of oscillatorylike nonlinear Hamiltonian systems, driven by a weak noise, is considered. A general method to find regions of stability in the phase space of a randomly driven system, based on a specific Poincaré map, is proposed and justified. Physical manifestations of these regions of stability are coherent clusters. We illustrate the method and demonstrate the appearance of coherent clusters with two models motivated by the problems of waveguide sound propagation and Lagrangian mixing of passive scalars in the ocean. We find bunches of sound rays propagating coherently in an underwater waveguide through a randomly fluctuating ocean at long distances. We find clusters of passive particles to be advected coherently for a comparatively long time by a random two-dimensional flow modeling mixing around a fixed vortex.