Vertical hydroacoustic structure of the Tropical Atlantic central and intermediate waters

Large-scale CTD survey data are used to calculate the acoustic velocity in the North Tropical Atlantic. It has been stated that a characteristic feature of the vertical hydroacoustic structure in this region is associated with the presence of numerous local sound channels in the subsurface and intermediate layers. Characteristics of these channels are given and possible causes of their origin are discussed. It is shown how local acoustic waveguides affect the sound beam trajectory.Translated by V. Puchkin.     

Hydrometeorological conditions in the north-eastern Arabian Sea shelf zone during the period of the trade winds' change and their impact on the formation of commercial fish shoals

This paper examines the oceanographic situation in the north-eastern Arabian Sea shelf area during the period when the trade winds change. The location and intensity of the discharge front there have been found to be dictated by tidal events and the wind régime. It is shown that commercial fish shoals move over the water column along with the front and that fish catches are largest when the front is steady.Translated by Vladimir A. Puchkin.     

Model of the water exchange through the Bosphorus (a hydrodynamic estimate of blocking conditions for the Bosphorus undercurrent

A three-dimensional linear model of the stationary water circulation in the Bosphorus due to the river's outflow, density differences at the ends of the straits, and win is considered allowing for the earth's rotation and the bottom topography. The channel approximation and the method of the separation of variables are used to obtain the analytical solution of the problem. The solution obtained describes the main circulation elements which are know from observations. The influence of different parameters on the formation of vertical and horizontal structures of the velocity field is analysed.Blocking conditions for the Bosphorus undercurrent are estimated. Possible variations in the structure of flows in the straits related to the regulated outflow of the rivers of the Black Sea basin are discussed.Translated by Mikhail M. Trufanov.     

The influence of the haline and thermal stages of convection on the vertical hydroacoustic structure of the upper layer of waters in the tropical Atlantic

The variability of the sound speed vertical distribution in high-salinity and freshened tropical waters has been computed using the intense convection model. It is shown that the most complicated transformation of theC(z) profile is induced by haline convection in freshened oceanic waters. Computation results are collated with observed data.Translated by Mikhail M. Trufanov.     

Manifestations of the Black Sea undercurrent in the density and hydrostatic pressure fields

Vertical kinematic structure of the geostrophic currents has been found to be correlated to the distribution of seawater density and hydrostatic pressure over depth. The conditions necessary for the existence of the undercurrent have been defined. On this basis, hydrological survey data compiled by the Marine Hydrophysical Institute in the Black Sea have been treated. Examples are given, which support theoretical deductions about the possible existence of the undercurrent beneath the Black Sea rim current. The undercurrent's parameters have been determined, along with the depths of the upper and lower boundaries and the mainstream velocity. Translated by Vladimir A. Puchkin.     

Ecologically Tolerable Impact Levels of Abiotic Factors in Water Bodies in Russia and Neighboring Countries: Dependence on the Geographic and Climatic Conditions

Largest river basins in Russia, Lithuania, Ukraine, and Uzbekistan are compared with respect to the admissible levels of the environmental physicochemical factors, the violation of which entails ecological disturbance of hydrobiont communities. The determination analysis of data is used to study the dependence of the degree of adaptation of limnetic ecosystems to external impacts on the sampling site (water column or ground), the latitude, climate, distance from sea, and the density of population in the region under study. Geographical and climatic classifications of regions are proposed based on the variability in the limits of environmental tolerance to abiotic impacts.     

Thermohaline characteristics of large-scale irregularities and frontal zones of the Tropical Atlantic

We determine the zones of maximum horizontal gradients of thermohaline characteristics and climatic frontal zones in the Tropical Atlantic and their behavior as functions of time and spatial variables on the basis of the climatic array of data on temperature and salinity. It is shown that the zones, where the maximum horizontal temperature, salinity, and density gradients coincide, are located in the northern and southern tropical frontal zones. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

North Brazil Current: Variability, stability and transport of waters

On the basis of the data of thein situ measurements of current velocities and other basic hydrophysical parameters (temperature and salinity) performed in the course of Cruise 41 of the R/VAkademik Vernadsky, we analyze the variability and stability of the North Brazil Current in winter. We also study the possibility of the influence of the baroclinic component of the horizontal drop of hydrostatic pressure on the vertical profile of the current velocity and estimate the intensity of the transport of waters. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Guiana current over North Brazil shelf and continental slope

Using thein situ currents measurements conducted during Cruise 41 of the R/VAkademik Vernadsky, we have considered the structure of the Guiana Current in winter over the shelf, continental slope and in the deep-water part of the ocean, adjoining the Brazilian coast. Regular variations of the current velocity with depth have been identified, and the current velocity's stability and variability determined. The paper examines how the barocline component of the hydrostatic pressure horizontal drop influences the current velocity's vertical profile. An attempt has been made to evaluate the current's transport. Translated by Vladimir A. Puchkin.     

Acoustic properties of surface water masses in the tropical Atlantic and their seasonal variability

The peculiarities of the vertical hydroacoustic structure of surface water masses in the tropical Atlantic are reported. The near-surface acoustic channel in areas of strong freshening of oceanic waters by continental discharge and rainfall is studied. Quantitative characteristics of the seasonal variability of the channel's parameters are given. The mechanism responsible for the long-range acoustic conductivity in the upper layer of waters is analysed. The areas of maximum horizontal refraction in the near-surface layer are identified and the refraction angles of acoustic rays determined.Translated by V. Puchkin.