Cloud filtration technique for the Black-Sea AVHRR data

We consider a version of the procedure of cloudiness recognition in the AVHRR images regionally adapted for the Black-Sea region. The threshold algorithms using the specific features of the formation of upward radiation in different spectral ranges are taken as basic. In studying the data obtained for the Black Sea, we analyze and modify the well-known algorithms of detection of the cloudy situations in the day and night time. The efficiency and disadvantages of the developed method are estimated by analyzing the results of processing of the satellite data obtained in 2005 and 2006.     

Modeling of decadal variations in the Black-Sea ecosystem

We consider the decadal evolution of the Black-Sea ecosystem on the basis of a three-dimensional coupled model consisting of the Black-Sea circulation model and a biogeochemical block. The circulation model is based on the widely used POM (Princeton Ocean Model) model. The calculated hydrophysical fields are interpolated then to levels of the biogeochemical model, which covers the upper 150-m layer. We demonstrate the close relationship between the interannual variation of hydrophysical fields and the evolution of the main elements of the ecosystem. The period under consideration (1992–2001) is characterized by the warming of the Black-Sea upper layer, which can be traced by the trend of a growing surface temperature. It follows from the results of modeling that the process of warming is also revealed in the subsurface hydrophysical characteristics and the dynamics of the main elements of the Black-Sea ecosystem.     

Climatic structure of the wind fields in the Black-Sea region

For the Black-Sea region, we perform the dynamic reanalysis of the data on atmospheric circulation for the period 1958–2001 by using the HadRM3P model with a space resolution of 25 km. We estimate the mean climatic atmospheric fields of vorticity and divergence of the wind velocity and study their space structure and seasonal variability. The climatic estimates of the annual course of vorticity of the wind velocity over the sea are presented. The obtained large annual average values of vorticity of the velocity reveal the predominant role played by the wind action in the generation not only of the seasonal variability but also of the mean cyclonic circulation of waters in the Black Sea.     

Monitoring of the Black-Sea Dynamics Based on Satellite Technologies

We present a survey of the principles and methods of satellite monitoring of the ocean, analyze the prospects of application of the data of satellite measurements to the operative diagnostics and prediction of circulation in the Black Sea, and discuss the physical foundations of remote sensing, the possibilities of contemporary equipment aimed at the observation of the sea surface from satellites, and the applicability of satellites as retransmitters of the data of measurements from free-drifting buoys. The contemporary oceanographic investigations carried out from satellites enable one to use the accumulated data for the numerical analysis of currents in seas and oceans in the model of general circulation as well as for the creation of a system of operative diagnostics and prediction of the state of marine environment. Examples of experimental realization of elements of the system of operative diagnostics of the state of the Black Sea based on the use of the satellite data are presented and the prospects of prediction of currents in the basin are analyzed.     

Registration of tsunamis in the open ocean

Abstract

The small tsunami of February 23, 1980, which originated near the southern part of the Kuril Islands was recorded by the bottom vibrotron sensor installed on the shelf near Shikotan Island and connected to the island observatory by underwater cable. The marigram of the tsunami is given and compared with marigrams obtained at shore tide gauges. Some spectral features of the records are discussed.     

Modeling of the Specific Features of Climate in the Black-Sea Region

By the method of cluster analysis, we obtain a collection of meteorological fields for six typical synoptic situations in Eastern Europe for 1982–1996. We study the possibility of evaluation of the climatic characteristics of the field of precipitations for the Black-Sea region on the basis of a mesoscale atmospheric model with the use of certain statistically selected typical situations as input data.     

Specific features of reverberation in the Black-Sea underwater sound channel

We consider the results of instrumental investigations of specific features of reverberation in the Black Sea and obtain qualitative dependences of the duration of volume reverberation on the parameters of the Black-Sea underwater sound channel, (width, drop of the sound velocity, and dimensions of the inhomogeneities of stratification). We also analyse the behaviour of the intensity of surface reverberation in the far-field zone of acoustic illumination and the influence of bottom reverberation on the detection of underwater objects. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Measurement of tsunamis in the open ocean

Abstract

The spectrum of long waves, which are a background to tsunamis, is analyzed on the basis of records of near‐bottom pressure sensors obtained in the Northwest Pacific during the first and second USA‐USSR expeditions on the investigation of tsunamis in the open ocean (1975 and 1978). Instrumental trends, tidal oscillations, and quasistationary longwave noise were contained in the records. Special filters were used to pick out small waves generated by the seismicity of the ocean bottom. A decrease of noise level from 10² cm (including tides) to 10°¹ cm could be reached. The level of long‐wave noise is found to depend on the instrument's location. Minimal disturbances in the records were observed at stations situated on the edge of the continental slope. The influence of cyclones passing over the instrument's site is deduced. It shows an increase in noise level on Nyquist frequency (0.5 min°¹), which possibly is caused by the action of swell generated by the cyclone. Seismicity of the region under investigation for the second expedition (August‐October 1978) is described, and the recurrence of tsunamis is estimated, including microtsunamis. Taking into account this analysis, records were filtered and sections corresponding to probable arrivals of tsunamis from most strong earthquakes were selected. The anomalous disturbance of ocean level with a height of about 0.5 cm was found. Presumably, it was generated by an earthquake with magnitude M = 6.     

Mathematical modelling of volcanic tsunamis

The height of widespread tsunami runup about the Bay of Plenty from various volcanic scenarios involving eruptions at White Island is shown to be insignificant in all cases considered, except for Krakatoa‐type explosions. The problem of localised inundation remains unanswered. Some definitions describing volcanic tsunami risk, introduced recently by J. Latter (Bulletin volcanologique 1982), are briefly mentioned. All numerical calculations assumed cylindrical symmetry and used a flux‐corrected Lax‐Wendroff algorithm to solve the modified shallow water equations of Peregrine.     

HF radar detection of tsunamis

This paper demonstrates that HF radar systems can be used to detect tsunamis well before their arrival at a coastline. We solve the equations of motion and continuity on the ocean surface using models to simulate the signals produced by a tsunami approaching the east U.S. coast. Height and velocity profiles are derived along with expressions for the radar-observed current velocities in terms of bathymetry and tsunami height and period. Simulated tsunami-generated radial current velocities are superimposed on typical maps of radial velocity generated by a Rutgers University HF radar system. A detection parameter is defined and plotted to quantify the progress of the tsunami, which is shown to be detectable well before its arrival at the coast. We describe observations/warnings that would have been provided by HF radar systems at locations in the path of the 2004 Indian Ocean tsunami.     

Relationship between the Beam Attenuation Coefficient and the Concentration of Suspended Matter in Black-Sea Waters

By using the results of simultaneous measurements of the beam attenuation coefficient and the concentration of suspended matter in water samples, we deduce the relationships between these parameters for wavelengths of 640, 660, and 677 nm. The proposed formulas are used for the evaluation of the concentration of suspended matter according to the data of optical measurements performed in cruises of research vessels. We present two maps of the distribution of suspended matter plotted for the north part of the sea in November–December 1991 and for the south part of the sea in July 1992.     

Analysis of the necessity and possibility of tsunami early warning on the Black-Sea coast

The catastrophic tsunami of December 26, 2004 in Southeast Asia revealed the necessity of creating tsunami early warning systems in the regions of the World Ocean where these systems are still absent but the potential hazard of tsunami generation exists. The Black Sea is one of these regions. We present the general characteristic of the tsunami hazard in the Black-Sea region and describe the most probable zones of tsunami generation, the specific features of tsunami propagation, and the parameters of tsunamis according to the data of observations and the results of numerical simulations. We also discuss the possibility of tsunami early warning on the basis of the operative data provided by the network of hydrometeorological and seismological observation stations existing in this region. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 57–66, September–October, 2008.     

Modelling of the ecosystem of the Black-Sea shelf zone near the estuary of the Danube

We analyze the results of numerical calculations performed according to the three-dimensional interdisciplinary model of an ecological system of the Black-Sea shelf zone near the estuary of the Danube. The complete system of equations of hydrothermodynamics is solved together with transport equations of the advection-diffusion-reaction type used to describe the transformation of a substance (nitrogen) between the components of the characteristic vectors of the ecosystem: plankton, detritus, and biogenic elements (nitrates). We describe the distinctive features of the circumcontinental distribution of components obtained as a result of numerical experiments and present arguments for the conclusion that the ecosystem of the Danube estuary water area plays the role of a buffer zone between the press of the Danubian biogenic pollutions and the neighbouring areas of the shelf zone and open sea. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Angle of energy flux at the origin of two major tsunamis

The energy flux of the Japan Sea Tsunami of May 26, 1983 radiated offshore causing the destruction of ships in Shimane Prefecture, the fourth worst area hit. In 1960, a tsunami from Chile attacked the Pacific coast from the Ryukyu Islands to Adak Island Alaska. The energy flux of the latter was similar to that of the former. The angle formed at the origin off the Chilean coast by the energy flux was 68°48 or possibly slightly larger. The coincidence between the angle given by this process and that by the directivity theory of Miyoshi (1977) is good. The Sanriku District is located approximately on the center line of this angle. Judging from the fact that the Sanriku District was attacked most severely in 1960, it can be suspected that the energy flux was a little more sharply directed than estimated by the theory. The equivalent angle in the case of the Japan Sea Tsunami, which attacked the area from the tip of the Noto Peninsula to the east coast of the Korean Peninsula, was only 45°30 and the smaller angle can be explained as a refraction effect of the Yamato Bank. The above information should be useful for warnings of future tsunamis.     

Deposits of the 1983 and 1993 tsunamis on the coast of Primorye

Deposits of the two strongest tsunamis of the 20th century have been found on the eastern coast of Primorye. The tsunamis had epicenters in the Sea of Japan west of the coast of Hokkaido. The distribution and preservation of deposits in bays of different geomorphological structure have been analyzed. The best defined sedimentary covers occur in the upper part of sections in low-lying areas of bay shores, where the wave runup was more than 3 m. The best preserved deposits have been observed in bays attributed to loworder streams. Variations of the structural composition of tsunami deposits formed by traction processes associated with the tsunamis have been analyzed depending on distance from the shoreline; the sources of material have been identified. Tsunami waves transported sand not only from beaches, ancient storm ridges, and terraces, but also from the underwater coastal slope; waves also grabbed material from estuarine lagoons and lakes located in the shore inundation zone. Deposits include marine diatoms with dominant sublittoral planktonic and benthic species, which suggests that the material was transported from a depth no more than 15 m. Deep-sea species of diatoms and their fragments have been encountered. Among freshwater diatoms are species with different ecological identities, indicating erosion and redeposition of material transported from various sources.     

On the problem of local tsunamis and possibilities of their warning

At present, the problem of predicting tsunamis with source earthquakes near the shoreline remains practically unresolved. It is shown that, in the Pacific region, 87% of tsunamigenous earthquake epicenters are located closer than 100 km to the shoreline and 67% are closer than 50 km. For a more detailed analysis, the area of the Pacific Ocean was divided into ten subregions: Kamchatka, the Kuril Islands, Japan, Indonesia, Australia and Oceania, South and Central America, Alaska, and the Aleutian Islands. Each subregion was analyzed individually. All the earthquakes from 1950 to 2003 with Ms >= 6.0 causing tsunamis with intensities I > 0 were processed. The ITDB/PAC 2004 database was used as the data source. For each subregion, mean and minimal travel times were calculated. The minimal travel times for all the regions except for a single one are less than 10 min. It is shown that, in the near earthquake zone, no tsunami alert based sea-level gauge data is possible. One probable solution could be based on detecting hydroacoustic signals that precede strong earthquakes in the near-shore zone.     

Relationship between the depth of visibility of Secchi disk and biooptical characteristics of the Black-Sea waters

We present the parameters of empirical relationships between the depth of visibility of Secchi disk and optical and biological characteristics of the Black-Sea surface waters. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Wave characteristic and morphologic effects on the onshore hydrodynamic response of tsunamis

While the destruction caused by a tsunami can vary significantly owing to near- and onshore controls, we have only a limited quantitative understanding of how different local parameters influence the onshore response of tsunamis. Here, a numerical model based on the non-linear shallow water equations is first shown to agree well with analytical expressions developed for periodic long waves inundating over planar slopes. More than 13,000 simulations are then conducted to examine the effects variations in the wave characteristics, bed slopes, and bottom roughness have on maximum tsunami run-up and water velocity at the still water shoreline. While deviations from periodic waves and planar slopes affect the onshore dynamics, the details of these effects depend on a combination of factors. In general, the effects differ for breaking and non-breaking waves, and are related to the relative shift of the waves along the breaking–non-breaking wave continuum. Variations that shift waves toward increased breaking, such as steeper wave fronts, tend to increase the onshore impact of non-breaking waves, but decrease the impact of already breaking waves. The onshore impact of a tsunami composed of multiple waves can be different from that of a single wave tsunami, with the largest difference occurring on long, shallow onshore topographies. These results demonstrate that the onshore response of a tsunami is complex, and that using analytical expressions derived from simplified conditions may not always be appropriate.     

Traces of ancient tsunamis in the coastal parts of the South China Sea

The results of geological and geomorphological investigations have shown that the South China Sea and its close coastal margins are in danger because of the possibility of a tsunami arriving from seismically active zones in the Philippines and Taiwan to the west and northwest coastal zones of the South China Sea. The collected data on paleotsunamis make it possible to date at least three such ancient catastrophes that have occurred in the last 1000 years (about 350, 650, and 960 years ago). The height of splashes of these ancient tsunami waves can be estimated. It was more than 7 m and in some places exceeded 15 m. The length of the sea coast covered by the paleotsunamis is estimated at several hundred (up to a first thousand) kilometers, which gives the opportunity to distinguish them from the ancient typhoons that are also typical of the region.