Hydrometeorological Coastal Integrated Researchin the North-Eastern Partof the Black Sea
V.S. Arkhipkin, S.S. Mukhametov
M.V.LomonosovMoscowStateUniversity, 119991 Moscow, Russian Federation
Tel: +7495 9392215 Fax: +7495 9328836
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Abstract
Department of Oceanography, Faculty of Geography of M.V.Lomonosov Moscow State University engage in field observations of hydrometeorological characteristics in the base of South Branch of the Shirshov Institute of Oceanology Russian Academy of Sciences more than 10 years. The study area is varied topography, occupies a mountain-foreland of the Caucasian Black Sea coast between the territories of the cities Novorossiysk and Tuapse, a length of about 90 km and a width of 8 to 30 km.
During this work gained wide array of oceanographic observations in the coastal zone of the north-eastern Black Sea. Studies are in the same time (late May - mid-July and late January - early February), during this period held steady continuous observation with a step for 5 minutes for the main meteorological parameters and hydrological-chemical parameters of sea water (temperature, salinity, pH , redox potential, dissolved oxygen, etc.), to engage in a comprehensive oceanographic survey of Gelendzhik Bay area (30 stations). Surface water samples took that to determine the hydrochemical parameters (pH, alkalinity, oxygen content, concentrations of phosphate, silicate and nitrate concentrations of some pollutants such as petroleum products) in laboratory conditions, as well as sampling for phytoplankton. Using Doppler profiler observations were carried out for currents and with the help of an acoustic wave recorder – wave observations and sea level.
Fig. 1: Area studies
Introduction
One of the distinguishing features of meteorological study area is the interaction of breeze and mountain-valley atmosphere circulation. Spectral analysis of observational data shows that the most energy-for the main meteorological variables (air temperature, atmospheric pressure, longshore and normal to the shore components of wind velocity) are variations of the daily periodicity. Contribution to the overall variability of wind speed normal to the shore was equal to two times more than the contribution of longshore component. This confirms the important role of local circulation, as not only a breeze, but the winds of mountain-valley circulation perpendicular coastline. Processes of large-scale energy transfer in the ocean-atmosphere system associated with the thermal contrast of air and water, and phase differences between the annual cycle of the thermal characteristics of the ocean and atmosphere [Lappo, 2004]. Mesoscale interaction between the ocean and the atmosphere is characterized by an exchange of properties and energy in the processes of daily variability. Diurnal changes, as well as seasonal, are quasi-cyclic processes. This circumstance allowed to apply to daily fluctuations, similar to the seasonal approach, based on the consideration of two-parameter phase diagram [Lappo, Gulev, Rozhdestvensky, 1990]. The rate of change in water temperature and the air is largely controlled by the regime breeze circulation in the atmosphere.
To analyze theprocessesin the coastalzonehas beenappliednumericaloceanmodels, University of Bergen (BOM),adaptedto theconditions ofthe study area. Grid spacingalongx andy -75mNumber ofsigmalevels- 24. Experiments were conductedto identify thecharacteristics ofthe reactionzone in thecoastalwaters ofvarioussynopticsituationstypicalforthe area.ПрослушатьНалатинице
The observations were made using an automatic weather station, "Vantage Pro" by "Davis Instruments", an automatic oceanographic probe YSI 6600, ultrasonic wave recorder remote «LOG_a Level» by «General Acoustics Company», Acoustic Doppler Current Profiler by «RD Instruments». Hydro-meteorological observations were conducted during the summer months (June-July) and winter (January-February) for 12 years (since 1999). Especially noticeable influence of local circulation on the weather appears while easing the pressure of wind and large-scale atmospheric flows, where over time, exceeding the characteristic period of meteorological processes, there is no change of air mass. In this case, the nature of weather and diurnal variation of meteorological variables is determined by properties located in the area of air masses, particularly its moisture content, which depends on the radiation and, consequently, the temperature regime. From this perspective, the study of meteorological processes on the northeastern coast of the Black Sea summer period is the most appropriate. At this time, the number of passing cyclones and atmospheric fronts decreases and the frequency of days with breeze circulation may be from 50 to 100% (Burman, 1969).
Sections of the main text
Spectral analysis of our observational data shows that the most energy-carrier for the main meteorological variables (air temperature, atmospheric pressure, alongshore and normal to the shore wind velocity component) are the fluctuations of the daily periodicity (1440 min). After eliminating the diurnal revealed two peaks of the spectral density (Fig. 2a-b).
a) b)
Fig. 2: The graphs of the spectral density normal to the shore component of wind velocity (a) and spectral density of air temperature in summer days with breeze circulation 1999-2011
The first corresponds to the period close to the semi-diurnal (10-17 h). This is explained by the fact that daytime and nocturnal manifestations of local circulation regimes (breezes, mountain-valley wind and slope winds) are independent processes. The second maximum falls on the oscillation period 30-60 h (1,5-3 day). Contribution to the overall variability of the wind velocity component normal to the coast two times greater than the contribution of alongshore component. This fact confirms the important role of local circulation, as not only a breeze, but the winds of the mountain-valley circulation are perpendicular to the coastline.
In the Gelendzhik Bay aquatory regularly conducted comprehensive oceanographic surveys of a single polygon, which contains about 30 stations (Fig. 3)
Latitude
Longitude
Fig. 3: The scheme of the stations at the site of Gelendzhik Bay
These works are taking place not only in favorable weather in the summer but in winter time. One of the most interesting processes taking place on the shelf of north-eastern part of the Black Sea in the winter – the formation of cold intermediate water. Formation of cold intermediate and deep waters occurs primarily when compacted during winter cooling (due to the impact of heat in the atmosphere and sea due to evaporation) and salinity (due to evaporation) of surface waters. These two processes are actively contributing to cold and dry continental winds. Cold winds increase the cooling, strong and dry – increased evaporation. Strong winds also increased wind mixing, which contributes to the destruction of the seasonal thermocline. Meteorological conditions of the Black Sea in winter are characterized by frequent westerly winds, which at times can be very strong, and bring to the surface of the sea is cold, dry air from the continent (continental polar air, or even continental arctic air). Water temperature at the surface of 9-7 °C and below, on the northwest shelf - to 0 °C, while in the northern part of it - to the freezing point. In the Black Sea, on the one hand, represented a vast north-west shelf of limited depth, strongly freshwater river runoff and a smaller area of the northeastern shelf, on the other – the two main cyclonic gyre in the open part. The main foci formation of intermediate cold waters of open sea in winter are associated with anomalously cold and salty spots in the centers of cyclonic gyres of the Black Sea. Permanent pycnocline is raised to 30-40 m and sometimes up to 20 meters, so it delays the exchange of properties vertically particularly strong, and increased density in the centers of most cycles. Convective mixing here, regardless of «severity» winter conditions, may develop much earlier and stronger than in other parts of the open sea.
Engaging in cyclonic circulation, the density currents generated on «domes» feed layer minimum temperature, which is gradually spreading throughout the deep part of the Black Sea and deepened in the continental slope to 100 m or more.
The sequence of formation of cold shelf waters in shallow areas of the shelf and in bays can be considered an example of Gelendzhik Bay. The increase in density is greatest, because the heat is removed from a thin layer and cooling more rapidly than in other, more distant from Markotkh Ridge through which the inflow cold dry air in the bay area. As a result, formed abnormally cold water is not very high salinity but significant density. Thus, under the force of gravity is generated by the density of the flow with downward movement of the slope of the shelf.
As seen in these images (Fig. 4,5), the lowest recorded water temperature in a period of intense cooling was 4.4 °C, maximum 8.8 °C, and the depth of minimum temperature, except for coastal areas, corresponds to the depth of the bay itself. At this depth is the core of the emerging here of cold intermediate water.
These countervailing trends clearly visualized on the temperature and density profiles constructed from the data section, normal to the wellhead alignment bay. Cold shelf waters, reaching its sliding back depth of 35 m, dropped on to the continental slope, and may be subject to the open sea.
Latitude
Longitude
Fig. 4: The distribution of the lowest water temperatures in Gelendzhik Bay waters – the core of cold intermediate water
Studies had shown, the combination of favorable oceanographic and meteorological factors on the northeastern shelf of the Black Sea (kinematics, water structure, dynamics and properties of air masses) in the winter cooling of surface waters causes that are located close to the low spurs of the Caucasus, the waters may form cold intermediate water.
Depth, m
Fig. 5: The temperature distribution on the longitudinal section of 04/02/2008
Leading factor in this case supports a small depth. As a result of the restructuring of the density field of winter there is the density currents, which are on the bottom of the shallow depths to greater. However, we must take into account that the parameters of the cold intermediate water reveal a strong dependence on the synoptic factors (direction, duration and wind speed and air temperature), so the process of their formation may be discrete in time and space in nature, slowing down and stopping, but reopening new force, under favorable conditions.
Synoptic variability with time scales of the inertial period to the season - one of the 5 major time-range variations in the state of the oceans and seas, along with inter-annually (many years), seasonal, diurnal and short-period range. However, it has become apparent only in 1970-1980's. That can be considered the "golden age" in the history of the problem. A comprehensive compilation of very numerous and important results of oceanographic research done in this period (Blatov, Tuzhilkin, 1990). In particular, it implies that the main carriers of synoptic variability in the oceans are:
1) forced to be immediately excited and supported by synoptic atmospheric processes (drift currents away from the coast, coastal upwelling / downvelling, deepening / shallowing bottom border of the upper mixed layer, etc.);
2) proper motion - subinertion gradient-vortex waves, Rossby, topographic, coastal trapped, frontal;
3) mesoscale eddies of various kinds, as a result of hydrodynamic instability of wave motions of the previous group. Among them, the whole of the oceans most energetic eddies (Blatov, Tuzhilkin, 1990).
The exception in this sense is a coastal zone of the oceans and seas, including the continental shelf and slope. Here most of the vortex collapses, forming a small short-lived vortices as a result of shear (horizontal gradient) between the rate of longshore currents rod and the shore, creating a regime of chaotic variability is close to fully developed turbulence in pipes and channels. The main carriers of the same distinct synoptic signal in the shelf-slope area, along with upwelling / downvelling serve as coastal trapped waves (CTW). Targeted and highly productive full-scale and theoretical studies of these processes are performed in the same 1970-1980-ies. off the coast of North and South America, Africa, Australia, Western Europe (see, eg, reviews Allen, 1980, Brink, 1982, 1983, 1991, Clarke, Thompson, 1984, Arkhipkin et al, 1987, Blatov, Tuzhilkin, 1990 Ivanov, Jankowski, 1992), clearly showed a close genetic relationship between them. Thus, coastal upwelling / downvelling almost always gives a good start ("triggers") CTW, which are distributed along the coast (leaving it in the northern hemisphere on the right) as alternating regions of divergence / convergence of longshore currents synoptic. Accordingly, these regions are associated with traveling in the same direction of a "wave" upwelling / downvelling that the process of moving can "pump up" the resonant wind effects (Clarke, Thompson, 1984, Brink, 1991). Depending on the geometric parameters of the shelf and slope, and water density stratification periods CTW ranged from 1 day to 2 weeks, the wavelengths - from tens to hundreds of kilometers, the phase velocity of 3-4 m / sec. Extremely large and diverse application of knowledge and scientific importance of these processes encourage them to intensive research in most of the coastal ocean regions with active business operations.
In the Black Sea the first studies of synoptic variability in the coastal zone - the wind-tide phenomena - were made long ago - a half century ago (Bogdanova, 1959, Bogdanov, Kropachev, 1959, Tolmazin, 1963). Over the next 30 years, despite clear evidence of high intensity of coastal upwelling, even he was given undeservedly little attention. In particular, in the most popular books on hydrology and water dynamics of the Black Sea (Filippov, 1968, Blatov et al, 1984, Hydrometeorology ..., 1991), this question has not been considered at all. The results of the first modern systematic study of coastal upwelling and CTW off the south coast of Crimea were set out in (Blatov, Ivanov 1992, Ivanov, Jankowski, 1992, 1993). They showed a close similarity of the properties of these processes in the Black Sea and in the above regions of the oceans. However, even after they sufficient activity in these areas of research of the Black Sea was not observed. It may be noted only a few full-scale and model studies of upwelling in the same southern coast of Crimea (Gawarkiewicz et al., 1999, Vlasenko et al 2002, Ivanov et al, 2005) and in the vicinity of. Snake (Smith, Mikhailova, 2008), as well as estimates of total variance and spectra of the synoptic variability of currents off the north-eastern coast of the Black Sea (Ovchinnikov et al, 1986, Titov, 1990, Titov and Savin, 1997). They show that in the Caucasian Black Sea coastal zone variance synoptic velocity variations are 1.5-2.5 times higher than the high-frequency dispersion. Exceeding the synoptic variance in water temperature over the high reached 3-5. The spectra of the variability allocated significant peaks at periods of 12, 8-10; 6 4.2 days.
In some ways, similar to the mentioned research ship and satellite observations of meandering longshore Basic Black Current and vortex at its seaward and coastal flanks. In general, these observations were made outside of the shelf zone and their results are summarized in the book (Comprehensive Research ..., 2002) can not be uniquely extrapolated into it. The most discussed of synoptic processes in these studies - nearly always traceable chain of anticyclonic eddies in the coastal side of dim moving along the coast to the northwest. Their dimensions are large longshore axis of 50-70 km, a small cross - 20-30 km. Between two consecutive vortices varies from 2 to 14 days. In a later study (Zatsepin et al, 2008) described the horizontal field vector currents in the anterior (front) part of such a vortex over the continental slope according to a towed acoustic Doppler current meters. Analyzing these results, however, it should be noted a number of features (distinct time intervals, and apparently reversible nature of longshore currents, synchronous reversal of the vectors on a fairly large distances along the coast and others) who are physically much more logical to interpret the wave in terms of CTW than with turbulent eddies in terms of shear.
Summarizing the review of the problem, we can say that the special studies of synoptic variability of temperature and salinity in the shelf zone of the Caucasian Black Sea, such executed by the southern coast of Crimea (Ivanov, Jankowski, 1993, Ivanov et al, 2005), has not yet been conducted. The purpose of this article - to fill this gap by observations at the Blue Bay in June-July, as well as archival data coastal hydrometeorological Gelendzhik station.
Conclusions
Results of the analysis of observational data of meteorological characteristics, temperature and salinity of water at the Blue Bay in the Russian Black Sea coast near the town of Gelendzhik in June-July showed a very intense synoptic thermohaline variability with time scales of several days, weeks, and 15 ˚C sweep respect to temperature and salinity of 1,5 ‰. The most important maritime events in the synoptic observations were upwelling of cold subsurface water and salt, and the subsequent invasion of the surface lens of warm and brackish water, which led to the formation of a barrier layer and heat significantly (up to 28,5 ˚ C) surface waters. In turn, this created an unfavorable ecological situation in the bay. Both events were not unique due to local weather conditions, the synoptic variability of which was rather weak. It is suggested that they are largely attributable, respectively, the divergent and convergent phases of coastal trapped waves, dynamic signs which were followed by parallel observations of currents in the expedition of Institute of Oceanology RAS. Wind effects were only an additional factor in certain periods of time reinforcing effect CTW. Thermohaline characteristics of lenses of freshened waters suggest their origin from the coastal district of Sochi. Analysis of the retrospective (archival) observations on the hydrometeorological Gelendzhik station showed that traced in June 1999-2011, the synoptic nature of the thermohaline variability in this region were repeatedly observed in June last year with a close match intensity, duration and phases of individual synoptic events. Thus, the results and findings can be considered fairly typical for the Russian Black Sea coastal zone.
References