We show in this paper that helical hydrodynamic turbulence can magnify perturbation seed eddies and that this can lead to the appearance of large-scale structures. The characteristic size of the structures which appear is much larger than the size of the turbulence containing the energy and it is determined by the ratio of the topological invariant to the turbulence energy. The evolution of the instability found in this paper is accompanied by a transfer of energy from smallscale to large-scale fluid motions. PACS numbers: 47.25.Cg, 47.20. + m

The interaction of a mean flow with a random fluctuation field is considered. This interaction is described by the averaged Navier-Stokes equation in which terms nonlinear in the fluctuation field are expressed in terms of the mean flow and the statistical properties of the fluctuation field, which is assumed to be homogeneous, isotropic, and helical. Averaged equations are derived using a functional technique. These equations are solved for a mean background flow that depends linearly on the position vector. The solutions show that large-scale vortices may arise in this system.

A field experiment was carried out in summer 2002 on an oceanographic platform near the coast of Crimea, in the Black Sea. For the first time, the spectral volume scattering function (VSF) was measured for a wide range of scattering angles (i.e., from 0.6 to 177.3 degrees) using a recently developed device. Our analysis revealed that the mineral particles are the primary component influencing the scattering and backscattering coefficient in the study area. The good correlation obtained between the backscattering coefficient b bp and the nonalgal particles absorption coefficient showed that the absorption efficiency of the mineral particles is high in the second half of the experiment. The ratio Chla/c p (where Chla is the chlorophyll a concentration and c p is the beam attenuation coefficient) did not correlate with the backscattering ratio and thus could not be used in this experiment as an alternative proxy to estimate the bulk composition of the particles. The spectral variation of b p (the scattering coefficient) and b bp (the backscattering coefficient) was less steep than what can be found in the open ocean waters. That was explained by the influence of the absorption on the scattering process, especially in the blue, as a consequence of the anomalous dispersion. The average backscattering ratio bp varied spectrally within 4%. Nevertheless, a high spectral variability of bp (around 30%) was observed suggesting that the use of a flat spectral variation is not accurate in coastal zones.

We present the description and preliminary results of the international subsatellite experiment carried out on the oceanographic platform located in the Black Sea (near the South Coast of Crimea in the region of Katsiveli). A brief description of the equipment and experimental procedure is given. Some preliminary results of the experiment, including the data on the behavior of biooptical parameters as functions of time and their correlation, are presented. These data cover a broad range of variation of the biooptical properties of the sea and can be used for the quantitative comparison with the data of the MERIS, MODIS, and SeaWiFS scanners.

We construct a simple model of seasonal variability of circulation in the Black Sea, which satisfactorily explains the data of altimetric satellite observations. The model is used to describe the nonstationary wind-induced currents in a round basin and study the trajectories of water particles in the surface layer of the sea. It is shown that, for nonstationary currents, these trajectories can be quite complicated. It is also assumed that Lagrangian mixing can be caused by the complex trajectories of water particles.

This paper is aimed to propose a theory of self-organization of large vortex motions in a turbulent medium. The hydrodynamical turbulence is an example of nonequilibrium systems commonly met in nature. Turbulence is usually understood as an unordered motion of a fluid such that the energy of a large-scale perturbation is transferred to random chaotic motions of smaller and smaller scales and eventually dissipates. This concept of turbulence seems to be inconsistent with coherent structures existing in a turbulent medium. In the present paper we show, however, that large-scale vortex motions arise in a turbulent medium, provided that this medium is homogeneous, isotropic, and gyrotropic. The scale of the generated vortices, L, is much greater than the correlation length of the turbulence, A, and is determined by the internal characteristics of the turbulence as L~E/I, where \(f\left\langle {\vec V\vec V} \right\rangle d\vec r\) is the turbulent energy and \(I = f\left\langle {\vec V \bullet \nabla \times \vec V} \right\rangle\) is the topological invariant. This result is obtained by direct averaging of the Navier-Stokes equation without use of phenomenological models. Some solutions of the averaged equations exhibit large-scale instabilities with the maximum of increment on the scale L. We should emphasize that the generated structures are not the remnants of the central flow (of the type of Karman vortices) but are produced just by the gyrotropic turbulence

Theoretical work on the stochastic nature and turbulence of plasmas is reviewed, and some new results are discussed. The relationships among the various criteria for a stochastic state are discussed (overlap of resonances and the condition of a local instability). Quasilinear equations are derived for a system which is becoming stochastic. The width of the stochastic layer which arises near a separatrix is derived. Functional and diagram formulations of strong turbulence are given. A method for eliminating the divergences in the Dyson diagram equations in all orders of perturbation theory is described. Explicit expressions are given for the contraterms. Turbulence spectra are found through the use of a scale-transformation group and a similarity theorem for a characteristic functional. It is shown that if the turbulence is gyrotropic then a large-scale instability occurs and generates coherent vortex structures.