Physical and hydrological characteristics of climatic frontal zones in the Tropical Atlantic

Climatic frontal zones are selected in the thermohaline fields of the Tropical Atlantic by analyzing the many-year-average seasonal database reduced to the nodes of a one-degree grid. We determine physical characteristics of the frontal zones, study their spatial and temporal variability, and reveal basic regularities of the appearance of frontal zones in the fields of thermohaline characteristics. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Interannual and seasonal variability of hydrometeorological fields in some regions of the Atlantic-European sector as a manifestation of the abnormal behaviour of the North-Atlantic Oscillation

We study the interannual and seasonal variability of hydrometeorological fields in some regions of the Atlantic-European sector. These low-frequency processes are analyzed depending on the index ΔP (an analog of the index of the North-Atlantic Oscillation). It is shown that the average value of the index ΔP over the winter natural synoptic season can be used for the determination of stable locations of the centre of the Azorean maximum in 1971–1980 and 1981–1990, the typical state of cloudiness in the Atlantic-European sector, and the fields of precipitations and atmospheric temperature in some regions of the Crimea. Typical anomalies of the fields of precipitations and atmospheric temperature over the west and south coasts of the Crimea are described. The signs of the anomalies of precipitations in the winter natural synoptic season are in good agreement with the signs of the corresponding anomalies of the field of cloudiness in the Black-Sea region. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

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     

Convection of salt fingers in theC-SALT region

We study possible mechanisms of mixing in the northwest part of the Tropical Atlantic (C-SALT) and show that homogeneous layers in the staircase structure can be observed across the entire frontal zone of the North Equatorial Countercurrent. In the central region of the frontal zone, one may observe horizontal motions of the upper parts of quasihomogeneous layers with respect to their lower parts and an essential role in the exchange processes is played by turbulence. The peripheral regions of the frontal zone are characterized by the presence of horizontal advection and isopycnic mixing. Far from the frontal interface, the principal contribution to the exchange processes is made by double diffusion. We demonstrate that, for the analysis of the vertical buoyancy fluxes caused by salt fingers, one can use both the Stern relation and the “law of 4/3”. Translated by Peter V. Malyshev and Dmitry V. Malyshev.     

Vertical structure of geostrophic currents in the fields of density of water and hydrostatic pressure

We analyze geostrophic currents with nonmonotonic vertical profiles, of velocity and present the distributions of the density of water and hydrostatic pressure corresponding to possible types of the vertical kinematic structure. To prove the existence of the indicated complex layered structures, we use, the data of instrumentalin situ measurements of currents in the Black Sea and in the west part of the Tropical Atlantic. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Analysis of the possibilities of aGALS-3 hydrophysical towed complex

We describe the characteristics of a towed complex used for measurements in the upper layer of the ocean under the conditions of periodic deepening and lifting (scanning) of a carrier with sensors connected with the ship by a weight-carrying cable of constant lengt. For a maximum scanning range of 0–200 m and a towing speed of up to 12 knots, the measurements were performed every 1.5–2.0 km. The minimum vertical scale of recorded temperature and conductivity inhomogeneities is 0.05–0.08 m. We present the results of measurements carried out by the towed complex in a section of the frontal zone in the north-east part of the Tropical Atlantic. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

North Brazil current: vertical structure

On the basis of the data ofin situ measurements of the velocities of currents and basic hydrophysical parameters (such as temperature and salinity) carried out during Cruise 41 of the R/VAkademik Vernadsky, we analyze the structure of the North Brazil Current near the continental slope and in the equatorial abyssal part of the ocean in winter, establish the regularities of changes in the current velocity with depth, and compare the structures of the North Brazil and Guiana Currents. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Rotation of orbital currents in the trains of internal solitons in the ocean

We analyze the results of measurements of currents in the trains of internal solitons on the New-York shelf of the Atlantic Ocean performed in the course of the Joint US/Russia Internal Wave Remote Sensing Experiment (JUSREX). It was discovered that the thermocline is characterized by an almost monotonic anticyclonic variation of the direction of orbital currents in the trains of solitons but the direction of waves in each train is practically constant. As a rule, the current significantly deviates to the left from the direction of waves in the leading soliton and approaches the indicated direction in the rear solitons of the train. The angular rotation current velocity corresponded to periods varying within the range 12–24h and, on the average, was close to the local inertial period. It is shown that this rotation cannot be caused by the distorting influence of advection of background shear currents but, most likely, is connected with the unknown properties of internal solitons in the rotating ocean. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Mechanism for the Formation of Temperature Anomalies in the Upper Layer of the North Atlantic

ORA-S3 oceanological reanalysis data for 1959–2011 is applied to analyze the role different factors play in forming advective heat transfer anomalies on an interannual–decadal scale in the upper mixed layer of the North Atlantic. Regions are revealed in which horizontal heat advection anomalies are determined by variations in current intensity, temperature gradients, and their joint influence. It is demonstrated that the contribution of different mechanisms responsible for advective heat transfer anomalies in the upper mixed layer to the total anomalies of advective origin varies fundamentally from one current to another in the North Atlantic. In the Gulf Stream area (after it separates from the continental slope), horizontal heat advection anomalies in the upper mixed layer result mainly from fluctuations in current intensity, while in the Caribbean Current and the Gulf Stream area (until its separation), they result from variations in the horizontal temperature gradients in the upper mixed layer. In the Labrador Current, both of these mechanisms have the same sign and approximately the same absolute values. In the East Greenland Current, they compensate each other. The contribution of anomalies in horizontal temperature gradients transferred by anomalous currents to the formation of heat transfer anomalies in the upper layer of the North Atlantic are, on the whole, relatively small throughout the water area. The areas of the North Atlantic and West Greenland currents are exceptions.     

Identification of mantle and lithospheric components of the gravity field by isostatic gravity anomalies

All anomalous masses of the Earth are reflected in the free air gravity anomalies and the geoidal undulations. The low viscosity of the asthenosphere significantly reduces the possibility of existence of density inhomogeneities in the layer. This fact provides some physical basis for the separation of the gravity field anomalies. It has been shown by power spectrum analysis of the free air anomalies and gravity field of isostatically compensated model of the lithosphere for the North Atlantic and adjacent areas of America, Europe and Mediterranean, that the attraction of isostatically compensated model is significant for any wave length of the field. It causes significant error in the interpretation if long wavelength constituents of the free air gravity anomalies are considered as a field of deep anomalous masses. The isostatic anomalies und isostatic geoid are free from the influences of isostatically compensated lithosphere. The characteristic feature of the isostatic anomalies power spectrum is a pronounced minimum at the wavelength of about 1000 km. The relative homogeneity of the asthenosphere may explain this minimum. It means that principal density inhomogeneities of the Earth's interior are separated by the asthenospheric layer. Such a minimum has not been observed at the power spectrum of free air anomalies being masked by corresponding wavelength of the field of isostatically compensated lithosphere. Isostatic anomalies that reflect the differences between the real structure of the lithosphere and its isostatically compensated model have wavelengths less than 1000 km. Isostatic anomalies with the wavelength more than 1000 km reflect the attraction of density inhomogeneities situated under the level of isostatic compensation. The basic features of power spectrum of isostatic anomalies are the same for oceanic and continental areas. The method based on Kolmogorov-Wiener filtration which consideres statistical characteristics of the field has been developed to divide the isostatic gravity anomalies into lithosphere and mantle components. For the North Atlantic and adjacent areas the field of mantle inhomogeneities has been determined.     

Characteristics of the mixing effect of small-scale internal waves in the upper layer of the Black Sea according to the data of fine-structure sounding

A method of statistical separation of fine-structure fluctuations according to their origin is applied to the analysis of the characteristics of mixing in a layer located below the summer temperature minimum in the Black Sea. The simplification of the procedure of numerical evaluation of the coefficient of vertical wave exchange enabled us to perform the comprehensive fine-structure processing of the data of regular surveys of the Black Sea with an aim to determine the spatial distribution of the field intensity of small-scale internal waves and the intensity of mixing caused by these waves in the analyzed layer. 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     

Incidence of flexural gravitational waves on the line of contact of two floating ice plates of different thickness

We analyze the influence of a rift in an ice field on the propagation of flexural gravitational waves in a basin of finite constant depth. The ice cover is simulated by two floating semiinfinite elastic plates of different thickness. We studied the dependence of the amplitude coefficients of reflection and transmission of waves incident on the rift on the frequency of running waves, the thickness of ice on both sides of the rift, and the type of contact boundary conditions at the rift. Translated by Peter V. Malyshev and Dmitry, V. Malyshev     

On the relationship between dynamic processes in the near-earth atmosphere and the tropical Atlantic surface temperature anomalies

A close correlation is found between dynamic processes in the near-earth tropical atmosphere, conditioned by air pressure anomalies in the Azor maximum, and the inter-annual ocean surface temperature variability in the north equatorial current area and in some other areas of the North Atlantic. A regression relation is proposed for calculating the sea surface temperature from the air pressure maximum in the Azor maximum. We discuss the anomalously high (low) upper ocean layer temperatures in the north equatorial current area induced by dynamic anomalies in the near-earth atmosphere and by the bottom topography.Translated by V. Puchkin.     

Trajectory and drift velocity of a sounding instrument in the field of nonuniform currents

We present a method for the determination of the trajectory of a sounding instrument and its drift velocity in the field of currents nonuniform in depth and develop special software for IBM/PC compatible computers. The proposed method and software are checked by using the well-known analytic solution of a similar problem given by Academician A. N. Krylov. We also consider some special examples of application of the developed method to the processing of the data of an OLT profilometer. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Generation of long waves in a basin of variable depth in the process of formation of a region of perturbations of atmospheric pressure

We perform the numerical analysis of the long-wave response of the free surface of a fluid in a basin of variable depth to the formation of an anomaly of the baric field for a finite period of time. In numerical experiments, we use the distribution of depths typical of the south coast of the Crimea. We also study the dependence of the dynamics of the sea level in the zone of the baric anomaly and in the shelf zone on the space and time scales of local changes in the field of atmospheric pressure in the open part of the basin. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Spectrophotometric and iodometric methods for the detection of hydrogen sulfide in the Black Sea: Comparison of the results of analysis

We discuss the results of analysis of published data and field and laboratory investigations aimed at the solution of the problem of comparabilityof the results of detection of hydrogen sulfide in the Black Sea by spectrophotometric and iodometric methods. We show that the reproducibility of the results of spectrophotometric analysis is higher than hat of the iodometric method only in the case where the content of sulfide in a sample is less than 10–30 μMl⁻¹. When larger concentrations are involved, the traditional iodometric analysis proves to be the most precise and reliable method for the detection of hydrogen sulfide in the Black-Sea waters. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

On the mechanisms behind salinity anomaly signals of the northern North Atlantic

Hydrographic time series from the northern North Atlantic throughout the 20th century show oscillations in temperature and salinity at more or less regular intervals. The Great Salinity Anomalies described during the 1970s [Dickson, R.R., Meincke, J., Malmberg, S.-A., Lee, A.J., 1988. The “Great Salinity Anomaly” in the North Atlantic, 1968-1982. Progress in Oceanography 20, 103-151.], during the 1980s [Belkin, I.M., Levitus, S., Antonov, J., Malmberg, S.-A., 1998. “Great Salinity Anomalies” in the North Atlantic. Progress in Oceanography 41, 1-68.], and during the 1990s [Belkin, I.M., 2004. Propagation of the “Great Salinity Anomaly” of the 1990s around the northern North Atlantic. Geophysical Research Letters 31(8), L08306, doi:10.1029/2003GL019334.] have distinct amplitudes, and all three of them were interpreted as low salinity anomalies propagating downstream through the anti-clockwise circulation system of the northern North Atlantic Ocean. Further inspection of time series from the Northeast Atlantic and the Northwest Atlantic over the past century shows, however, several other distinct negative anomalies of lesser amplitudes. Additionally, a number of high salinity anomalies can be identified. The present paper analyses further the propagation of the negative and positive anomalies and links them together. It is shown that they have varying speeds of propagation, and that the varying speeds are correlated across the North Atlantic. We propose that varying volume fluxes in and out of the Arctic Basin is the causal mechanism behind the anomaly signals, and that the North Atlantic Oscillation (NAO) partly has influence on the flux variations described. Periods of large decadal-scale amplitudes of the NAO coincide with periods of large decadal-scale oscillation in the marine climate.     

Manifestations of water dynamics in the coastal zone in the field of breaking of wind waves

In the coastal zone, as a result of mixing of waters, it is difficult to identify turbulent phenomena with a spatial scale of 0.1–1 km accompanied by strong vertical flows according to the data of measuring temperature. On the basis of the data of direct measurements, it is shown that turbulent structures are well pronounced in the field of breaking of wind waves. We deduce empirical estimates of the response of the intensity of wave breaking to the magnitude of divergence of the current and develop a theoretical model of the influence of inhomogeneities of currents on wave breaking capable of describing the experimental data. Translated by Peter V. Malyshev and Dmitry V. Malyshev