Spheroidal Earth’s free oscillations _0Sn, where n is the number of oscillation nodes along a meridian between the poles, are observed during seismically quiet days. The seismometer measurements of these background Earth’s free oscillations with n = 12—65, located at frequencies of 2—7 mHz (periods ~8—2 min), show that the Earth’s free oscillations are caused by atmospheric processes. The following mechanism for excitation of the Earth’s free oscillations is proposed. During strong storms high waves generate oceanic internal gravity waves, which excite, in turn, Earth’s free oscillations acting on the seabed. The present study is devoted to the search for the excitation source of background Earth’s free oscillations 0S2, which is located at the frequency of about 0.3 mHz (period of about 54 min) and is the lowest frequency Earth’s free oscillations. We have used the continuous measurements of the vertical (Z) output signal of STS-2 seismometer at Collm, Germany (51.3°N, 13.0°E), for the full year of 2002. The spectral analysis was applied over the 5-day window sliding along the annual series of the seismometer measurements with 1-day step. The values of power spectral density at the frequencies of the ₀S₂ multiplet and the frequencies close to them are matched with the values of the Arctic oscillation index, which characterizes the intensity of dynamic perturbation of the atmosphere in the Northern hemisphere. It is found that the correlation coefficients between these values are positive and statistically valid. So, it is shown for the first time that the background Earth’s free oscillations ₀S₂ can be excited by dynamic processes in the atmosphere, just as it is for highfrequency Earth’s free oscillations.

The mechanisms of influence of stratified turbulence to the formation of the atmospheric boundary layer electric state and the variability of electric parameters are discussed. As a result of the field observations and numerical modeling, it is found that the development of convection in the atmospheric boundary layer reduces the electric conductivity near the surface. The stochastic electrodynamic model, reproducing the evolution of the vertical profiles of electric conductivity and aeroelectric field intensity in the lower troposphere of mid-latitudes land undisturbed by precipitations and thunderstorms, is used for the calculations. The results show that the increased turbulence generation due to convection accompanied by an increase of the turbulent kinetic energy and the variance of vertical turbulent velocity tends to more intensive vertical mixing of radon and its short-lived daughters. In this case, the turbulent transport of radon leads to more uniform vertical distribution of the electric conductivity and an increase of the aeroelectric field intensity in the surface layer. Estimations of the variability of electric conductivity and aeroelectric field intensity, caused by radon emissions, air ionization, charge separation on the electric conductivity inhomogeneities, turbulent transport of radioactive elements and space charge, are performed. It is assumed that altitudinal aeroelectric profiles can be objective and operative parameters of the atmospheric boundary layer turbulent conditions.

We make a review on the modelling efforts devoted to better understand the complex oceanography of the Strait of Gibraltar, where Atlantic waters enter the Mediterranean Sea as a surface flow, and Mediterranean outflowing waters spread into the interior of the North Atlantic forming a prominent basin-scale termohaline anomaly at mid-depths. Besides the mean exchange flows relevant phenomena include tides, high amplitude internal waves, meteorologically forced subinertial oscillations, mixing, and involve a wide-range of spatio-temporal scales. The remarkable progress achieved in understanding and modelling the ocean processes in the Strait of Gibraltar allows now undertaking new societal demands and scientific challenges. One societal demand is given by the increasing need of operational oceanographic information as a support tool for decision-makers in an area considered as one of world's busiest shipping lanes, with an increased risk of maritime accidents and environmental pollution. We present an Operational Oceanography system for the Strait of Gibraltar responding to that demand. On the other hand, new scientific challenges call for the need of developing perspective-modelling studies accounting for process and scale interactions. Using a global ocean general circulation model with regional high resolution around the Iberian Peninsula we are able to resolve the local-scale at the Strait of Gibraltar and the Gulf of Cádiz while focusing on the basin scale. As a result, we find that tidally-induced local-scale processes in the Strait and in the Gulf of Cádiz appear to have a drastic impact on the distribution of Mediterranean outflow waters in the Atlantic basin.

The integrated water circulation of the South China Sea in the area of coastal Vietnamese Current during transitional spring period (May 1999) has been calculated on the basis of numerical modeling. The South China Sea considerably influences the climate regime in South-East Asia, including the Far East of Russia. Here the tropical cyclones of the destructive power coming from the western Pacific or incipient in the South China Sea are developed. This specified year was selected in connection with this period of large-scale international expedition Fisheries Association of South-East Asia and Japan, the data of which are presented by Vietnamese colleagues. Spring season is used as an example of the transition from winter to summer because it’s poorly investigated. Synoptic processes in the region significantly influence the seasonal the nature of Vietnamese Сurrent. This current is directed from north to south in winter under the influence of the northeast monsoon, thus forming the cyclonic water circulation. This current is directed in the opposite direction in the summer under the influence of the southwest monsoon, forming an anticyclonic circulation. The calculations were performed for the synoptic situation, which is characterized by the presence of tropical cyclone in the southern part of the South China Sea. Results of modeling have showed that two anticyclonic and separating its cyclonic gyres exist in the specified period in the studied area. As a result, two zones of different water modifications within the Vietnamese Current are formed: water masses are transported from south to north in the northern and southern parts of the region (summer regime), and in the central part — from north to south (winter regime). On this basis, it was concluded about a transitional character of the chosen time interval when influence has not yet left winter and already coming summer monsoons affects.

Materials of the large experiment, which included installing of five moorings in the northern part of Aniva Gulf which located in the southern part of Sakhalin Island, were analyzed. Four acoustic Doppler current-meters were installed in the coastal area in June 2003 and removed in the late autumn. Current Doppler profiler was placed in the deep part of the Gulf in the area of the soil dumping point, current measurements were carried out during 2 months. During the warm season, under the influence of typical S-SW winds, cyclonic circulation formed in the coastal zone of the Gulf. After adjustment of the wind field to the winter monsoon winds with typical NW winds, coastal currents change their direction. The intense anticyclonic inertial currents with an amplitude of about 20 cm/s and a period of about 16.6 hours was found in the dumping area (three times observed within 3—5 days). They were most pronounced in the intermediate layer and weaker near the top and bottom. During the second decade of July, these currents and flow with a period of about 2 weeks occurred when passing over the area of measurements of the atmospheric perturbation with anticyclonic vorticity of the wind. Special investigations of bottom soil showed no significant changes in its characteristics in the process of dumping.

During field work in the summer of 2012 in the White Sea in the south-eastern part of the Throat, and Western and Eastern Solovetsky Salma were carried out experimental studies of short-term variability of the temperature field, having the characteristic properties of internal waves with time scales less than an hour. For piecewise constant and piecewise exponential distribution approximations analytical solutions of the boundary value problem with the depth and density found corresponding dispersion curves for internal waves. The calculation of the eigenfunctions numerical and analytical method produced three density distribution models: exponential (linear), two-layer and three-layer. The characteristics of waves (length, height, period, phase and group velocity), as well as vertical wave structure by calculating its own functions for density models and numerical calculation of the eigenfunctions for an arbitrary density distribution. The smallest difference between the numerical and analytical assessment refers to Eastern Solovetsky Salma. The dispersion characteristics of internal waves for the region Throat derived analytically, are highly dependent on the evaluation of Brunt-Vaisala frequency. It was found that the waves, called uncharacteristic, covered subsurface water column in the neck, and the area in the vicinity of the density of the thermocline in the western Solovetsky Salma.

This work employs numerical methods of viscous fluid dynamics for determination of hydrodynamic and hydroacoustic characteristics of the oscillating wing as the major structural element of the fin propulsor. Verification of the calculation methods with subsequent analysis of the fin propulsors of more complex designs was carried out by means of comparison of numerical results against respective analytical solutions and experimental data. Hydrodynamic characteristics were determined based on the numerical solution of the Reynolds-averaged Navier—Stokes equations supplemented by the realizable model of turbulence. Rotation of the wing in the water flow was ensured by the mechanism of «sliding computation meshes» implemented in many computing software packages of mechanics of fluids and gases. Hybrid approach to mathematical modelling was described to assess the noise produced by the fin propulsor in the far field using the Ffowcs Williams—Hawkings equation. Verification of this method was based on comparison of the calculated results against experimental values of levels of acoustic pressure when viscous gas flows around the cylinder. The calculated values of pressure fluctuation amplitudes in the far field produced by wing oscillations were compared against analytical estimations obtained by means of modelling of the effect that concentrated fluctuating force (presented as dipole) produces on fluid. The proposed calculation approaches can be used for designing perspective propulsion systems based on the oscillating wing.

The optimal frequency plays an important role in design and usage of different sonar both passive and active. For simplicity the optimal frequency calculation is usually fulfilled with the use of the formulas not taking in account the peculiarities of the signal and sea noise propagation in the concrete conditions. It can entail the mistakes in the optimal frequency choosing. The work is devoted to the passive and active sonar optimal frequency investigation. Investigations were fulfilled taking in account all the factors influencing on the optimal frequency, including signal propagation anomaly and vertical sea noise anisotropy. The investigation showed that in the real ocean conditions the optimal frequency always lower then simplified calculation gives. And the difference depends on the hydroacoustic conditions in the ocean region. The greatest difference takes place in the conditions of positive ray refraction when the propagation of the acoustic energy occurs by reflection of sea surface. In these conditions the optimal frequency value strongly depends on sea state — the greater sea state the lower optimal frequency. The greatest influence of signal propagation anomaly takes place on the distances from 3 to 30 km: on the smaller distances the conditions have weak influence on the signal propagation; on the larger distances the main influence on optimal frequency has spatial fading.

The problem of determining of the marine environment characteristics by fixed values of the emitted and reflected acoustic signals, received from different scatterers without direct characteristics measurement with ship dipping probes, is relevant and useful. Impact assessment of the vertical sound velocity distribution in the waveguide from the surface to the sea bottom is made immediately prior to use of various hydroacoustic equipment. The usability of information contained in the received acoustic signal, reflected from the target, to obtain the marine environment characteristics, can significantly simplify the nature of the efficient use of acoustic ship equipment. This work studies solution algorithms of return problems of restoration of sound speed vertical distribution while sounding from the ship in water medium acoustic sound diffuser, relatively big single or multiple small, in the volume, limited by characteristics of antenna directivity, sea surface and sea bottom. It is shown that the more acceptable (for practical use) is the algorithm of restoration of sound speed vertical distribution with the method of linearization while sounding on the move in the sea medium single sound diffusers, having dimensions more than a radiated signal wavelength.