On the formation of atmospheric seasonal precipitation in the Black Sea region

The climatic features of the formation of precipitation and their correlation with the baric situation in the Atlantic-European sector are studied on the basis of the data of the Sevastopol and Feodosiya coastal hydrometeorological stations. As the source data, we use the data arrays of daily precipitation at these stations in 1900–2005 and the data of reanalysis of the fields of atmospheric pressure in the Atlantic-European sector. The comparative statistical analysis of daily precipitation for the wet and dry summer and winter seasons and the estimates of extremely high levels of precipitation for the specified periods of repeatability are presented. The existence of the dependence of occurrence of wet and dry winter seasons in Sevastopol and Feodosiya on the large-scale baric fields in the Atlantic-European sector is confirmed. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 43–51, July–August, 2008.     

Investigation of Frontal Zones in the Karkinitskii Bay

On the basis of the data from the databank of the Marine Hydrophysical Institute of the Ukrainian National Academy of Sciences and the data of regional marine hydrometeorological stations, we present the characteristics of the seasonal variability of temperature and salinity frontal zones and background gradients in waters of the Karkinitskii Bay. We determine the locations of the frontal zones, the values of their gradients, horizontal scales, repetition, connection with weather conditions, inflow, and direction of propagation of salt and freshened waters in the bay in different seasons of the year. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 30–42, July–August, 2005.     

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     

Reconstruction of the space and time variability of thermohaline fields in the Sevastopol Bay

The aim of the present work is to reconstruct the space and time variability of the three-dimensional fields of currents, temperature, salinity, and density in the Sevastopol Bay under the influence of the actual external factors in 1999. For this purpose, we use a version of the numerical multilayer model on the σ-coordinates. A vast array of the data of observations accumulated as a result of regular monitoring of the Sevastopol Bay contains, in particular, the data on the sea-surface temperature measured with six-hour intervals (at the hydrometeorological station located near the center of the bay) and almost monthly vertical profiles of temperature and salinity obtained at seven hydrological stations. The comparison of the numerical results with the data of observations enables us to conclude that, in general, the model fairly correctly describes the space structure and rearrangements of the fields of temperature and salinity. Among the most important distinctions, we can mention the fact that the fresh river water penetrating into the bay is mixed with seawater faster than predicted by the model. We also discuss the causes of these distinctions. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 23–39, September–October, 2008.     

Application of biooptical relationships for the determination of the characteristics of state of marine media in the optical monitoring of the black-sea waters performed by using transparency meters

As applied to the transparency meter installed in the hydrometeorological complex aimed at monitoring the Black-Sea coastal waters, we show the possibility of evaluation of various characteristics of state of the marine medium according to the data of measurements of the beam attenuation coefficient in two spectral regions: short-and long-wave. For this purpose, we use biooptical relations established on the basis of the experimental data accumulated for the Black Sea. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 37–45, March–April, 2008.     

On the Statistical Structure of Hydrometeorological Fields in the North Atlantic

We study the possibility of detection of statistically significant trends as a characteristic of low-frequency variability of hydrometeorological fields in the North Atlantic on the basis of relatively short time series. We use the monthly data of the Russian Hydrometeorological Center for 1957–1990 and analyze their statistical structure. It is shown that significant linear and quadratic trends can be detected in the fields of most hydrometeorological characteristics of the North Atlantic. The residual signal is approximated by using the first-order autoregressive model. Typical values of the coefficient of autoregression vary within the range 0.3–0.6 (for different hydrometeorological characteristics of the North Atlantic). The maximum correlation is observed for the fields of sea-surface temperature and humidity, whereas the minimum correlation is typical of the fields of wind velocity and the difference between the temperatures of water and air.     

Time variability of technogenic radioactivity in the Black and Mediterranean Seas

We analyse the time variability of the fields of Cs-137 concentration in the surface waters of the Black and Mediterranean Seas in 1986–1998. It is shown that more contaminated Black-Sea waters affect the levels of concentration of this radionuclide in the east part of the Mediterranean Sea. We also study the influence of atmospheric processes and water exchange through Bosporus on the radioecological situation in the east part of the Mediterranean Sea and its coastal area. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Observed vs. predicted variability in non-algal suspended particulate matter concentration in the English Channel in relation to tides and waves

The study of water clarity is essential to understand variability in biological production, particularly in coastal seas. The spatial and temporal variability of non-algal suspended particulate matter (SPM) in surface waters of the English Channel was investigated and related to local forcing by means of a large satellite dataset covering the study area with a spatial resolution of 1.2 km and a daily temporal resolution. This analysed dataset is a time series of non-algal SPM images derived from MODIS and MERIS remote-sensing reflectance by application of an IFREMER semi-analytical algorithm over the period 2003–2009. In a first step, the variability of time series of MODIS images was analysed through temporal autocorrelation functions. Then, non-algal SPM concentrations were assessed in terms of site-specific explanatory variables such as tides, wind-generated surface-gravity wave amplitudes and chlorophyll-a (Chl-a), based on three statistical models with fitting parameters calibrated on a dataset of merged MERIS/MODIS images gathered from 2007 to 2009 over the whole English Channel. Correlogram analysis and the first model highlight the local patterns of the influence of the tide, especially the neap–spring cycle, on non-algal surface SPM. Its effect is particularly strong in the central and eastern English Channel and in the western coastal areas. The second model shows that waves prevail as driver at the entrance of the English Channel. The most sophisticated of the three statistical models, although involving only three explanatory variables—the tide, waves and Chl-a—is able to estimate non-algal surface SPM with a coefficient of determination reaching 70% at many locations.     

Statistical structure of the large-scale fields of temperature and salinity in the Black Sea

In order to reconstruct the large-scale temperature and salinity fields by the method of optimal interpolation of the archival data, we compute the correlation functions and analyze the space and time variations of the statistical structure of the fields. On the sea surface, the thermohaline fields are spatially inhomogeneous. Thus, the correlation functions are anisotropic in the region of the northwest shelf and close to isotropic in the inner parts of the sea. The values of correlation length vary from season to season. In the layer of pycnocline, the temperature and salinity fields are anisotropic. In the zonal direction, the correlation length is 2–3 times greater than in the meridional direction. The indicated anisotropy becomes stronger in the winter season and weaker in the summer season as a consequence of the seasonal variability of large-scale circulation. We study the dependence of the error of reconstruction of the fields by the method of optimal interpolation on the form of approximation of the correlation functions with regard for anisotropy. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 51–65, January–February, 2008.     

Mesoscale structure of the fields of vertical velocity and vorticity of winds over the Black Sea

On the basis of a simple stationary linear model and a contemporary nonlinear model, we study the mesoscale characteristics of the fields of vertical velocity and vorticity of winds over the Black Sea. It is shown that, in the idealized case (without taking into account the coastal features), the temperature contrast between the land and the sea in both models leads to the formation of circulation cells in the coastal zone. However, the mountainous features prove to be the main factor affecting the process of circulation for the actual synoptic situations. We present the map of monthly average vorticity of the surface winds constructed according to the nonlinear mesoscale model with a resolution of 30 km for January 1996–2001. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 52–61, January–February, 2005.     

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.     

Investigation of the characteristics of surge phenomena in the Sea of Azov

We present the results of numerical simulation of currents and sea level for the Sea of Azov. In calculations, we use a three-dimensional nonlinear mathematical model taking into account the tangential wind stresses. We present the results of numerical analysis of the fields of currents and the amplitudes of oscillations of the sea level at the coastal stations as functions of the maximum velocity and the period of constant action of the west wind. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 12–25, January–February, 2008.     

Temporal and spatial variabilities of Japan Sea surface temperature and atmospheric forcings

In this study, we used the National Centers for Environmental Prediction monthly sea surface temperature (SST) and surface air temperature (SAT) data during 1982–1994 and the National Center for Atmospheric Research surface wind stress curl data during 1982–1989 to investigate the Japan Sea SST temporal and spatial variabilities and their relations to atmospheric forcing. First, we found an asymmetry in the correlation coefficients between SST and wind stress curl, which implies that the SST variability at the scales of the order of one month is largely due to atmospheric forcing. Second, we performed three analyses on the data fields: annual mean, composite analysis to obtain the monthly anomaly relative to the annual mean, and empirical orthogonal function (EOF) analysis on the residue data relative to the summation of the annual mean and the monthly anomaly. The first EOF mode of SST accounts for 59.9% of the variance and represents the Subpolar Front. The temporal variation of the first EOF mode implies that the deep Japan Sea could be cooler in cold seasons (November–April) of 1984–1987. Third, we computed cross-correlation coefficients among various principal components and found that the atmospheric warming/cooling is the key factor causing intra-seasonal and interannual SST variabilities.     

One-dimensional nonstationary model of vertical exchange in the Black Sea with regard for the mechanism of winter convection in the surface layer

We construct a one-dimensional nonstationary isopycnic model of vertical exchange in the Black Sea with regard for the processes of draining and transformation of waters of the Sea of Marmara (or “plume”), vertical diffusion, and the action of winter convection in the upper layer. It is assumed that mixing in the basin is local in space and time and that the winter wind action remains constant from year to year in the analyzed version of the model. The temperature of the upper mixed layer introduced to simulate the winter conditions is regarded as the principal external variable factor. Within the framework of the accepted restrictions, the model enables us to study the annual and interannual variability of the thermohaline characteristics and hydrochemical parameters in the water column of the sea. As an example, we perform the numerical analysis of the periodic action of external thermal conditions on the characteristics of the system with a period of six years. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 3–21, September–October, 2006.     

Interdecadal modulation of interannual atmospheric and oceanic variability over the North Pacific

The interdecadal modulation of interannual variability of the atmosphere and ocean is examined over the North Pacific by using Wavelet Transform combined with Empirical Orthogonal Function (EOF) or Singular Value Decomposition (SVD) analysis. For the period of record 1899–1997, the interannual variability of the wintertime Aleutian Low, identified by either the North Pacific Index or the leading eigenvector (EOF-1) of North Pacific sea level pressure (SLP), exhibits an interdecadal modulation. Interannual variance in the strength of the Aleutian Low was relatively large from the mid-1920s to mid-1940s and in the mid-1980s, but relatively small in the periods from 1899 to the mid-1920s and from the mid-1940s to the mid-1970s. The periods of high (low) interannual variability roughly coincide with pentadecadal regimes having a time averaged relatively intense (weak) Aleutian Low. Consistent with this SLP variability the interannual variance in the zonal wind stress is strengthened in the central North Pacific after the 1970s. The SLP EOF-2, which is related to the North Pacific Oscillation, exhibited a strengthening trend from the beginning of this century to the mid-1960s. After the 1970s, the interannual variance of SLP EOF-2 is generally smaller than that in the period from 1930 to 1970. Similar interdecadal changes in interannual variance are found in expansion coefficients for the first two EOFs of the Pacific sector 500 hPa height field for the period 1946–1993. EOF-1 of Pacific sector 500 hPa corresponds to the Pacific/North American (PNA) teleconnection pattern, while EOF-2 is related to the Western Pacific (WP) pattern. The relative influence of the atmospheric PNA and WP interannual variability on North Pacific SSTs appears to have varied at pentadecadal time scales. Results from an SVD analysis of winter season (December–February) 500 hPa and North Pacific spring season (March–May) SST fields demonstrate that the PNA-related SST anomaly exhibited larger interannual variance after the 1970s, whereas the interannual variance of the WP related SST anomaly is larger before the 1970s. Correlations between the coastal North Pacific SST records and gridded atmospheric field data also change on interdecadal time scales. Our results suggest that the SST records from both the northwest and northeast Pacific coasts were more closely coupled with the PNA teleconnection pattern during the periods of 1925–1947 and 1977–1997 than in the regime from 1948 to 1976. Teleconnections between ENSO and preferred patterns of atmospheric variability over the North Pacific also appear to vary on interdecadal time scales. However, these variations do not reflect a unique regime-dependent influence. Our results indicate that ENSO is primarily related to the PNA (WP) pattern in the first (last) half of the present century. Correlation coefficients between indices for ENSO and PNA-like atmospheric variability are remarkably weak in the period from 1948 to 1976.     

Seasonal variations of wind and waves over Taiwan waters

We here investigate the frequency and intensity of oscillations in oceanographic data within intraseasonal time scales using spectral analysis of surface wind and wave time-series data collected at off-island weather stations or moored buoys around Taiwan. Data from marine weather stations were used to trace atmospheric conditions, while we used buoy data to examine sea states. The spectra and wavelet scalogram of the wind fields revealed oscillations with a period of around 20–33 days, and the energy density of the wind field at the off-island stations was stronger than that at the data buoy stations. However, the wavelet scalogram of the wave height measured at the buoy stations was stronger than its associated wind field. This long-period oscillation is consistent with the wavelet scalogram of the wind field calculated from the off-island weather stations. About 20–33 day oscillations exist within intraseasonal variations, which are closely linked to the atmospheric environment and to wind and ocean wave fields. Oscillations with a period of 5–10 days are a pronounced feature over northeastern Taiwan waters during the winter season and can be interpreted as the wave pattern following synoptic weather systems.     

Hydrographic Structure and Transport of Intermediate Water in the Kuroshio Region off the Boso Peninsula, Japan

Hydrographic structure and transport of intermediate water were observed in the Kuroshio region south of Japan, focusing on the 26.6–27.5σ_θ density in six cruises from May 1998 through September 2001. In the section off the Boso Peninsula where the Kuroshio exfoliates eastward, the intermediate water was clearly clustered into three groups meridionally composed of the coastal water, the Kuroshio water and the offshore water. Compared with the Kuroshio water characterized by warm, salty water transported by the Kuroshio, the coastal and offshore waters significantly degenerated due to mixing with cold, fresh waters originated from the subarctic region: the former was affected by alongshore spread of the coastal Oyashio and the latter by direct intrusion of the new North Pacific Intermediate Water (NPIW) into the southern side of the Kuroshio current axis. Particularly the offshore water showed higher apparent oxygen utilization (AOU) in layers deeper than 26.9σ_θ while it showed lower AOU in layers shallower than 26.9σ_θ, which indicated that colder, fresher and higher AOU water was distributed on the southeastern side of the Kuroshio in deeper layers. In May 1998, the Oyashio-Kuroshio mixing ratio was estimated to be typically 2:8 for the offshore water on the assumption of isopycnal mixing. Moreover, northeastward volume transport of the Kuroshio water was obtained from geostrophic velocity fields adjusted to lowered acoustic Doppler current profiler (LADCP) data to yield 6.1 Sv at 26.6–26.9σ_θ and 11.8 Sv at 26.9–27.5 σ_θ. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reciprocal sound transmission measurement of mean current and temperature variations in the central part (Aki-nada) of the Seto Inland Sea,Japan

A 30 km-range reciprocal sound transmission experiment was carried out on the line connecting Honshu and Shikoku (the first and fourth biggest main Japanese islands, respectively) in the central part (Aki-nada) of the Seto Inland Sea, Japan, during March–May 2010 to measure the mean current and temperature variations over the sea. The range-averaged current along the sound transmission line was estimated to have a mean and standard deviation of (3.8–4.4) ± (1.7–1.8) cm/s after converting the travel time difference data into currents, including a fortnightly tidal variation in the range of ±30 cm/s. The positive mean current implies slow water movement from the west to east through Aki-nada. The range-averaged speed of sound was estimated by converting from the mean travel time or one-way travel time into the speed of sound, and further converted into temperature for fixed values of salinity and depth, according to the standard speed of sound formula. Besides the precise measurement (to an accuracy of 0.01°C) of semidiurnal and diurnal tidal variations and seasonal warming, the temperature data showed periodic variations with periods of 7.0 and 21.1 days that had never been observed in Aki-nada before. This study suggests that reciprocal sound transmission is a powerful technique for the long-term accurate measurement of mean current and temperature variations in coastal and inland seas.     

Soft- and hardware for the reception and treatment of satellite and reference data and their application to monitoring hydrometeorological fields

The paper describes the functional scheme of the soft- and hardware complex designed to receive, to treat and to disseminate satellite and reference hydrometeorological data. The complex displays a high degree of integration and unification of soft- and hardware techniques and packages. The operation of the complex is studied through the monitoring of cloud fields in the Atlantic-European section of the Northern hemisphere during the winter-time synoptic season of 1995–1996. The complex is shown to be capable of identifying large-scale cloud anomalies and of estimating their coherence in the individual regions of the Atlantic-European zone. Translated by Vladimir A. Puchkin.     

Spatial and Temporal Scale Variations of Sea Surface Temperature in the East Sea Using NOAA/AVHRR Data

Sea surface temperature fields in the East Sea are composed of various spatial structures such as eddies, fronts, filaments, turbulent-like features and other mesoscale variations associated with the oceanic circulations of the East Sea. These complex SST structures have many spatial scales and evole with time. Semi-monthly averaged SST distributions based on extensive satellite observations of SSTs from 1990 through 1995 were constructed to examine the characteristics of their spatial and temporal scale variations by using statistical methods of multi-dimensional autocorrelation functions and spectral analysis. Two-dimensional autocorrelation functions in the central part of the East Sea revealed that most of the spatial SST structures are anisotropic in the shape of ellipsoids with minor axes of about 90–290 km and major axes of 100–400 km. Two dimensional spatial scale analysis demonstrated a consistent pattern of seasonal variation that the scales appear small in winter and spring, increase gradually to summer, and then decrease again until the spring of the next year. These structures also show great spatial inhomogeneity and rapid temporal change on time scales as short as a semi-month in some cases. The slopes in spectral energy density spectra of SSTs show characteristics quite similar to horizontal and geostrophic turbulence. Temporal spectra at each latitude are demonstrated by predominant peaks of one and two cycles per year in all regions of the East Sea, implying that SSTs present very strong annual and semi-annual variations. This revised version was published online in August 2006 with corrections to the Cover Date.