On the problem of the computation of spectra of small-scale inhomogeneities in hydrophysical fields of the ocean

A novel form of correlation window employed to calculate the spectral density of a random process using a Fourier transform of the correlation function is proposed. It is shown that, concerning its metrologic characteristics, the value of the spectral density obtained does not yield the best autoregression estimates. A fast recurrent estimational algorithm is suggested to increase the efficiency of the calculational procedure.Translated by M. M. Trufanov.     

Short-range forecast of hydrophysical fields in the eastern part of the Black Sea

On the basis of an analysis of the results of modeling and a forecast of the basic hydrophysical fields in the easternmost part of the Black Sea for 2010–2012, the features of annual variability of regional circulating processes in this part of the sea basin are investigated. A forecast of a hydrological mode is made on the basis of the regional forecasting system developed at the Institute of Geophysics at Javakhishvili State University in cooperation with the oceanographic centers of the Black Sea riparian countries within the frame-work of the ARENA and ECOOP EU international scientific and technical projects. The regional system is one of the components of the Black Sea basin-scale Nowcasting/Forecasting System. The analysis of the material cumulated for the registered period shows that the easternmost water area of the Black Sea is a dynamically active zone where there is a continuous formation of different circulating processes considerably distinguished from each other.     

The study of intermittent hydrophysical fields in the vicinity of the frontal zone

CTD data provided by the MGI-4204 and MARK-III probes are used to study the quasistationary subpolar front structure in the north-western Sea of Japan. In order to provide further insights into the intermittent scalar hydrophysical fields, the method of inhomogeneity identification using temperature pulsations calculated by the moving interval is suggested. The experimentally-derived inhomogeneity distribution is satisfactorily approximated by the exponential law.Translated by V. Puchkin.     

Numerical modelling of the seasonal variability of hydrophysical fields in the Black Sea

The results of research into the seasonal variability of hydrothermodynamic characteristics of the Black Sea are presented. These have been obtained using field data on the fields of temperature, salinity, and wind, and by mathematical modelling. The seasonal variability of the current and heat content fields and of the cold intermediate layer and other hydrophysical characteristics is discussed.Translated by Mikhail M. Trufanov.     

Spatial and temporal variability and monitoring of hydrophysical fields of the Black Sea

As part of the Russian-Ukrainian program “The Black Sea as a Simulation Model of the Ocean,” the monitoring of the marine environment is considered using modern measuring systems. On the basis of historical and contemporary observation data, we estimate the spatial and temporal scales of dominant processes in the Black Sea. We describe the main measuring systems used to monitor the structure and variability of the hydrophysical fields. Examples characterizing the specific features of the Black Sea processes are presented.     

Numerical analysis of hydrophysical fields on the northwestern shelf of the Black Sea

A numerical experiment with assimilation of hydrological observational data from a survey in October 2007 on the northwestern shelf of the Black Sea was carried out using the hydrodynamic model with nonlinear equations of motion, equations of heat and salt advection, and data assimilation. The results of this calculation are compared with thermohydrodynamic fields obtained without taking into account temperature and salinity measurements. It is shown that allowance for the observation data leads to qualitative and quantitative differences in the structure of the hydrophysical fields. Mesoscale eddies and intense jet streams that agree with satellite observations were found in the field of currents and were investigated. These eddies are not resolved in low-resolution field experiments.     

An ocean data assimilation system and reanalysis of the World Ocean hydrophysical fields

A new version of the ocean data assimilation system (ODAS) developed at the Hydrometcentre of Russia is presented. The assimilation is performed following the sequential scheme analysis–forecast–analysis. The main components of the ODAS are procedures for operational observation data processing, a variational analysis scheme, and an ocean general circulation model used to estimate the first guess fields involved in the analysis. In situ observations of temperature and salinity in the upper 1400-m ocean layer obtained from various observational platforms are used as input data. In the new ODAS version, the horizontal resolution of the assimilating model and of the output products is increased, the previous 2D-Var analysis scheme is replaced by a more general 3D-Var scheme, and a more flexible incremental analysis updating procedure is introduced to correct the model calculations. A reanalysis of the main World Ocean hydrophysical fields over the 2005–2015 period has been performed using the updated ODAS. The reanalysis results are compared with data from independent sources.     

Numerical experiment aimed at modeling the hydrophysical fields in the sea of Marmara with regard for Bosporus and Dardanelles

We performed a long-term prognostic experiment aimed at the investigation of the process of formation of the hydrodynamic structure of the Sea-of-Marmara waters with regard for the influence of Bosporus and Dardanelles. It is shown that the mutual adaptation of hydrophysical fields and their adjustment to the physical and geographical conditions of the sea proceed as a result of the action of rapid (tens of days) and slow (several tens of years) mechanisms of adaptation. An S-like jet current directed from Bosporus to Dardanelles was formed. Two stable anticyclonic formations are well visible in the central part of the sea. In deeper layer, an abyssal jet current was formed as a result of penetration of heavy Mediterranean waters. The established specific features of the circulation of waters in the Sea of Marmara are confirmed by the data of observations. We conclude that the principal features of the dynamics of waters in the Sea of Marmara are formed under the influence of two straits. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 28–41, May–June, 2007.     

Numerical experiments on estimating the accuracy of four-dimensional analysis of hydrophysical fields using a quasi-geostrophic model of currents

The relationship between the results of four-dimensional (4-D) analysis and the approximations employed in the assimilation scheme, as well as the initial fields, is studied. The contribution made by a procedure of correcting the horizontal velocities by theT, S data to the increase of the quality of the data obtained is estimated. Numerical experiments were carried out on the data of measurements made in the observation site located in the Newfoundland energy-active zone in August 1985.Translated by Mikhail M. Trufanov.     

Numerical modeling of hydrophysical fields of the Black Sea under the conditions of alternation of atmospheric circulation processes

The hydrological regime of the Black Sea in the conditions of permanent alternation of atmospheric circulation processes was investigated on the basis of a baroclinic prognostic model of the sea dynamics. In the model, variations in the wind action were expressed as permanent alternation of 24 wind types characteristic of the Black Sea basin throughout the year. Thermohaline impact of the atmosphere was taken into account by specifying the annual trends of temperature and salinity at the sea surface, which was established from multiyear means of these parameters. The problem was solved numerically on the basis of the method of two-cycle splitting with the use of the grid with a horizontal spacing of 5 km. Results of the numerical experiment showed that, under the influence of a strong nonstationarity of atmospheric processes, the water circulation in the upper layer of the Black Sea changes qualitatively and quantitatively. The upper 20–30-m layer of the sea is particularly sensitive to atmospheric circulation variations. For any character of atmospheric circulation, the Black Sea circulation below this layer is nearly always cyclonic with internal cyclonic rotations.     

Four-dimensional analysis of the variability of hydrophysical fields in the tropical atlantic and on the shelf of guinea

The problem of monitoring of the mesoscale variability of hydrophysical fields in the shelf zone is considered. The usefulness of the data available in regional information centres is discussed. The possibility of monitoring the dynamics of the oceanic fields in the tropical Atlantic encompassing separate observation sites is demonstrated using the oceanographic databank of the scientific research centre (CERESCOR) in Conakry-Rogbane as an example. The results of assimilation of the hydrophysical survey data derived on the shelf in a telescopic model of the region are given.Translated by Mikhail M. Trufanov.     

Short-period variability of hydrophysical fields and internal wave characteristics during a semidiurnal tidal cycle on the White Sea shelf

Experimental data obtained in the summer of 2011 in three White Sea continental shelf areas with different stratification are analyzed. The measurements were conducted using a unified procedure that combines frequent oceanographic stations (scanning) and deployment of moorings. It is shown that the tide-induced variability of the thermohaline fields and internal waves is of different types. A shelf area is detected where intense short-period internal waves are observed during every tidal cycle and their contribution to water mixing is significant.     

Numerical modeling of the influence of exchange through the Bosporus and Dardanelles Straits on the hydrophysical fields of the Marmara Sea

A long-term (18 years) prognostic experiment on the formation of the Marmara Sea hydrodynamic structure driven by the exchange through straits with zero atmospheric forcing is carried out using a numerical nonlinear circulation model. The seasonal variability is taken into account by specifying the water temperature in the Bosporus. It is shown that the mutual adaptation of hydrophysical fields and their adjustment to the physical and geographical conditions of the sea are caused by rapid (tens of days) and slow (several tens of years) adjustment mechanisms. An S-shaped jet current directed from the Bosporus Strait to the Dardanelles is formed in the upper 20-m layer. A cyclonic eddy is periodically formed near the northern boundary of the Marmara Sea. An anticyclonic pattern is well defined in the central part of the sea. In deeper layers there is an abyssal jet current formed by the inflow of the high-density Aegean water to the Marmara Sea. These features of the Marmara Sea circulation are confirmed by observational data.     

Four-dimensional analysis of the hydrophysical fields in the tropical Atlantic using a complete non-linear model of currents: Numerical simulation andin situ data treatment

This paper reports the results of a numerical modelling experiment on estimating the accuracy of four-dimensional analysis using the twins technique.In situ temperature and salinity data collected in the tropical Atlantic are treated using a special algorithm. Some features resulting from the disagreement between the hydrophysical fields at the time of assimilation are discussed.Translated by V. Puchkin.     

Estimation of the long-term variability of hydrophysical characteristics of the Black Sea based on the assimilation of the climatic hydrological fields L and altimetry data

To study the long-term variability of the thermohaline and dynamic characteristics of the Black Sea, we use three versions of climatic fields, namely, the fields reconstructed in the model according to the old (1903–1982) and new (1903–2003) hydrological climatic data arrays of temperature and salinity and according to the data of satellite altimetry. The analysis of the altimetry-based climatic fields confirms the distinctions (established earlier according to the old and new data arrays) in the seasonal variability of the integral characteristics of temperature and salinity and in the structures of hydrophysical fields in the sea. It is shown that, in the winter-spring season, the thermohaline fields reconstructed according to the new and altimetry data arrays are characterized by a small elevation of the halocline (pycnocline) and the upper boundary of the cold intermediate layer. In all seasons, the altimetry-based surface geostrophic currents contain numerous mesoscale eddies with different signs of rotation. Moreover, in all seasons, the Rim Current reconstructed according to the altimetry data is characterized by a narrower jet almost along the entire its length. This jet is especially intense near the coasts of West Anatolia. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 3–17, July–August, 2006.     

Asymptotic detection performance of discrete power and higher-order spectra estimates

Several detection statistics are compared in the frequency domain based on the asymptotic probability of detection (APD) criterion. They include second-order, fourth-order, normalized fourth-order, and kurtosis estimates. The results show that for randomly occurring signals which can be characterized as non-Gaussian, the fourth-order, normalized fourth-order, and kurtosis estimates can have higher asymptotic probability of detection levels compared with second-order estimates. But only for the normalized fourth-order and kurtosis estimates do the results seem significant. Moreover, if a second-order estimate of the noise is available to normalize a fourth-order estimate of signal and noise, the resultant normalized fourth-order estimate has higher asymptotic probability of detection levels even for Gaussian signals. This result holds only when there is a significant positive covariance between the numerator and the normalizing noise sample in the denominator. On the other hand, if an independent noise sample is used to normalize a second-order or fourth-order estimate, the overall performance based on the asymptotic probability of detection will be degraded compared with the unnormalized second-order or fourth-order estimates, respectively.     

Specific features of the variability of atmospheric processes and hydrophysical fields near the west and southwest coasts of Crimea on time scales from interdiurnal to long-term

We present the results of analysis of the variability of hydrometeorological and hydrophysical fields near the west and southwest coasts of Crimea on scales varying from 1–100 days to 1–11 yr according to the data of long-term routine (4–8 h) observations performed at the coastal marine hydrometeorological stations. New methods of filtration and spectral analysis are used to reveal the characteristic time scales of variability including the quasiperiodic and periodic components and study the physical processes responsible for the indicated variability. Special attention is given to the analysis of correlation between the periodic variability of the fields in the atmosphere and in the coastal zone on different time scales. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 22–36, January–February, 2006.     

Sea-bed characterisation and classification from the power spectra of side-scan sonar data

This work is concerned with the automatic characterisation and classification of the sea-bed for side-scan sonar trace power-spectra.A parametric model of side-scan sonar trace power-spectra is developed from the equation for the magnitude frequency response of a Butterworth filter. The model's parameters are optimised to give a least squares fit with observed spectra. Three of the optimised parameters are used to define features.     

A comparison of several wave spectra for the random wave diffraction by a semi-infinite breakwater

A comparison of the diffraction of multidirectional random waves using several selected wave spectrum models is presented in this paper. Six wave spectrum models, Bretschneider, Pierson–Moskowitz, ISSC, ITTC, Mitsuyasu, and JONSWAP spectrum, are considered. A discrete form for each of the given spectrum models is used to specify the incident wave conditions. Analytical solutions based on both the Fresnel integrals and polynomial approximations of the Fresnel integrals and numerical solutions of a boundary integral approach have been used to obtain the two-dimensional wave diffraction by a semi-infinite breakwater at uniform water depth. The diffraction of random waves is based on the cumulative superposition of linear diffraction solution. The results of predicted random wave diffraction for each of the given spectrum models are compared with those of the published physical model presented by Briggs et al. [1995. Wave diffraction around breakwater. Journal of Waterway, Port, Coastal and Ocean Engineering—ASCE 121(1), 23–35]. Reasonable agreement is obtained in all cases. The effect of the directional spreading function is also examined from the results of the random wave diffraction. Based on these comparisons, the present model for the analysis of various wave spectra is found to be an accurate and efficient tool for predicting the random wave field around a semi-infinite breakwater or inside a harbor of arbitrary geometry in practical applications.