Black Sea Currents

The results of our studies of the currents of the Northern and Middle Caspian Sea differed significantly from the ideas that were most widespread. Therefore, we sought to compare them with published results from studies in other bodies of water. Gradually, we moved from studies of Caspian currents to studies of the nature of specific types of currents - wind, thermohaline, quasi-permanent circulations, long-wave, inertial, etc. in various reservoirs - in the Black Sea, in the Sea of ​​Okhotsk, in lakes Ladoga, Huron, etc. ., in those reservoirs for which it is possible to find measurement results.

This approach significantly expands the amount of experimental data suitable for analysis. We can compare current parameters in different bodies of water. This will allow us to better understand the properties of the studied processes of formation and existence of flows. The main research methods were invented during studies of the currents of the Northern and Middle Caspian Sea.

Let us consider the results of instrumental observations of currents in various seas and large lakes.

2.1. Black Sea Currents

The area of ​​the Black Sea is 423,488 km. The greatest width along the parallel is 42°21′ N. – 1148 km, along the meridian 31°12′ E – 615 km. Coastline length 4074 km.

Rice. 2.1. Black Sea water circulation diagram. 1 – Annular cyclonic current (ACC) – average position of the rod; 2 – CCT meanders; 3 – coastal anticyclonic eddies (SAEs); 4 – cyclonic eddies (CV); 5 – Batumi anticyclonic vortex; 6 – Kaliar surfactant; 7 – Sevastopol surfactant; 8 – Kerch surfactant; 9 – quasi-stationary cyclonic gyres (Kosyan R.D. et al. 2003).

The general circulation of the Black Sea waters - the Main Black Sea Current (Rim Current) is characterized by cyclonic movement of waters (Fig. 2.1). Its main structural element is the Annular Cyclonic Current (RCC). Near the Caucasian coast, the CCT occupies a strip along the coast 50-60 km wide and carries its waters in a general direction to the northwest. The centerline of the flow can be traced at a distance of 20-35 km from the coast, where speeds reach 60-80 cm/s. This current penetrates to a depth of 150-200 m in the summer, 250-300 m in the winter, sometimes to a depth of 350-400 m. The current core experiences wave-like oscillations, deviates either to the right or to the left from its average position, i.e. This jet the current meanders. In Fig. 2.1. the most common idea of ​​the structure of the Black Sea currents is presented.

The results of current measurements carried out over a period of 5 months in coastal waters in the northeastern part of the Black Sea are shown in Fig. 2.2.

In the figures we see that the currents cover the entire water column, the changes are synchronous at all horizons.

Rice. 2.2. Fragment of the time sequence of half-hour current vectors from December 20 to December 23, 1997. Point 1 – horizons of 5, 26 and 48 m; point 2 – horizons 5 and 26 m; point 3 – horizon 10 m (Kosyan R.D. et al. 2003).

These studies did not filter to identify long-period wave currents. The measurements lasted 5 months, i.e. It is possible to show about 5 periods of variability of long-period wave currents and their variability at different points, differences and common features as they move away from the coast. Instead, the authors provide explanations that are consistent with traditional views.

Rice. 2.3. Location of instruments off the southern coast of the Crimean Peninsula at points 1–5 (Ivanov V. A., Yankovsky A. E. 1993).

Rice. 2.4. Variability of current speed at measurement points 3 and 5 (Fig. 2.12) at a horizon of 50 m. High-frequency oscillations with a period of 18 hours. And less filtered using a Gaussian filter. (Ivanov V. A., Yankovsky A. E. 1993).

Measurements of currents in the coastal zone using autonomous buoy stations (ABS) were carried out off the southern coast of the Crimean Peninsula in the Black Sea at 6 points on 4 horizons from June to September 1991 (Fig. 2.3). (Ivanov V. A., Yankovsky A. E. 1993).

One of the main tasks is the study of waves captured by the shore. Long-wave currents with a period of 250-300 hours have been recorded. and amplitude up to 40 cm/s (Fig. 2.4). The phase propagated westward at a speed of 2 m/s. (Note that the value of the phase velocity is obtained from calculation, and not from the difference in the time of passage of the wave at two adjacent points).

Water circulation in the upper layer of the Black Sea is shown using drift data (Zhurbas V.M. et al. 2004). More than 61 drifters were launched in the Black Sea, which were carried by the current of large-scale circulation along the coast.

Rice. 2.5. Trajectory of drifter No. 16331 in the southwestern part of the Black Sea. The numbers on the trajectory are the day that has passed since the drifter was launched (Zhurbas V.M. et al. 2004).

The patterns of drifter advancement show the patterns of currents. The most common misconception about the nature of currents in the Black Sea: cyclonic circulation currents are jet meandering current. Meanders, breaking away from the main jet, form vortices. The authors demonstrate such a “vortex” in Fig. 2.5.

The following figure (2.6) shows the variability of the components of the speed of movement (current) of the drifter along the trajectory. The periodic variability of the current speed is clearly visible. The period of variability is from 2 to 7 days. The speed varies from - 40 cm/s. up to 50 cm/s, but the average speed (thick line) is close to zero. The drifter moves along a circular path. It reflects the movement of a water mass of a wave nature.

Bondarenko A.L. (2010) shows the path of one of the drifters in the Black Sea (Fig. 2.7), and the variability of the drifter’s movement speed along the trajectory (Fig. 2.8). Just as in the previous work, it is clear that currents of a wave nature are observed, and not a jet, meandering current. The path taken by the drifter during the initial period of its voyage attracts attention. The starting point (0) is in the center of the western part of the sea.

Rice. 2.6. Time series of drifter velocity components 16331. Ut is the longitudinal component of the velocity (+/- east/west, respectively), Vt is the latitudinal component [Zhurbas V.M. et al. 2004].

According to ideas (Fig. 2.1), this point is located outside the CCT. But we see that the drifter made a cyclonic path along a stretched almost ellipse, then moved southwest for 20 days. the direction where he got into the CCT and moved in it the entire further path. From this trajectory it is possible to calculate the flow velocity in different sections of the trajectory, and from (Fig. 2.8) the periodicity of the r.f. and n.ch. variability of this speed.

Rice. 2.7. Drifter's path in the Black Sea ( Bondarenko A.L., 2010).

The measurement examples discussed above show that the Main Black Sea Current, the Circular Cyclonic Current (ACC), is the resulting movement of long-period wave currents. The understanding of the geostrophic nature of the CCT currents and its meandering is erroneous. The period of variability of wave currents in the northern part is 260 hours. As we move along the coast, due to the unevenness of the coastline and bottom surface, the components of the current velocity across the coast become comparable with the components along the coast, the trajectories of drifters acquire a ring-shaped shape. The period of variability is greatly reduced.

Rice. 2.8. AND variability of the speed of movement of the drifter along the trajectory shown in Fig. 2.7.(Bondarenko A.L., 2010).

there is a so-called main Black Sea Current(VERT). It spreads throughout the Black Sea perimeter. This flow is directed counterclockwise and forms two vortex flows, the so-called rings.

This phenomenon is scientifically called “Knipovich glasses”. Nikolai Mikhailovich Knipovich was the first hydrologist who noticed and described this phenomenon in detail.

The acceleration imparted to seawater by the rotation of the planet is the basis for the characteristic direction of this movement. In physics, this effect is called “Coriolis force”. But, due to the fact that the Black Sea has a relatively small water area, a significant impact on the main The strength of the wind also has an effect. Due to this factor, the main flow The Black Sea is very changeable. Sometimes it happens that it becomes faintly noticeable against the background of other sea currents of a smaller scale. And it happens that the speed of the main Black Sea current exceeds one hundred centimeters per second.

In the coastal Black Sea waters, eddy currents are formed with the opposite direction to the main one. Black Sea current direction - the so-called anticyclonic gyres. Such eddies are especially pronounced near the Anatolian and Caucasian coasts. In these regions, longshore currents in the surface layer of the Black Sea are usually determined by the wind. The direction of such currents can change during the day.

There is a special type of local Black Sea current called the draft. Tyagun is formed during a storm (strong sea waves) near gently sloping sandy shores. The principle of this currents lies in the fact that the sea water flowing onto the shore does not retreat equally evenly over the entire area of ​​the tide, but along channels formed in the sandy bottom. Getting caught in the current of such a jet is very dangerous, since, despite all the efforts of the swimmer, he can be carried far from the shore directly into the open sea.

To get out of such a current, you need to swim not straight to the shore, but diagonally, this way it is easier to overcome the force of the receding water.

The current of “dragons” is one of the little-studied phenomena that is associated with waves.

The “tyagun” current is the most dangerous type of coastal current; it is formed due to the outflow of sea water, which was brought to the coast by waves. There is a well-established opinion that the “dragon” is pulled under the water; this is not true; the waves carry it away from the shore.

The power of the tug is high; it can pull even very experienced and strong swimmers with it from the shore. A person caught in a “thrust” should not fight it and try to swim straight to the shore by any means; the best option for salvation would be to move diagonally. This way you will be able to gradually leave the range of action of the thruster, this will allow you to save energy and stay afloat, as well as wait for help. It is also possible for the victim himself to gradually reach the shore on his own, trying not to return to the area of ​​influence of this dangerous phenomenon.

This phenomenon can be observed; in many ports of the Black Sea, ships moored to the pier suddenly begin to move from time to time and move along the piers, seemingly under the influence of some force. It happens that such a movement is so powerful that the steel mooring ends cannot withstand the pressure, because of this, cargo ships are forced to stop loading and unloading operations and go to roadstead. Tyagun can form not only during a storm, but also in completely calm seas.

There are several hypotheses about the formation of the draft, but they all define the draft as a consequence of the approach of a special type of sea waves to the port gates, which are difficult to notice with the naked eye. These waves are called long-period; they create an oscillation period much longer than ordinary waves visible to people. By periodically creating strong fluctuations in the mass of water located in the port waters, these waves cause the movements of ships moored at the pier.

The formation of this phenomenon, which poses a danger to fleet vessels, is being studied both in our country and abroad. The ongoing research work provides scientific and practical recommendations on the rules for mooring ships during the “thrust”, as well as advice on the construction of safe ports that will dampen the energy of this wave.

In the Black Sea there is Main Black Sea Current(Rim Current) - it is directed counterclockwise along the entire perimeter of the sea, forming two noticeable rings (“Knipovich glasses”, named after one of the hydrologists who described these currents). The basis of this movement of water and its direction is the acceleration imparted to water by the rotation of the Earth - the Coriolis force. True, in such a relatively small water area as the Black Sea, the direction and strength of the wind are no less important. Therefore, the Rim Current is very variable, sometimes it becomes poorly distinguishable against the background of smaller-scale currents, and sometimes its jet speed reaches 100 cm/s.

In the coastal waters of the Black Sea, eddies of opposite direction to the Rim Current are formed - anticyclonic gyres, they are especially pronounced along the Caucasian and Anatolian coasts.

Local coastal currents in the surface layer of water are usually determined by the wind; their direction can change even during the day.

A special type of local coastal current - draft- forms on flat sandy shores during strong sea waves: the water flowing onto the shore does not retreat evenly, but along channels formed in the sandy bottom. Getting caught in such a current is dangerous - despite the efforts of the swimmer, he can be carried away from the shore; to get out, you need to swim not straight to the shore, but diagonally.

Vertical currents: rise of water from depth - upwelling, most often occurs when driven away coastal surface waters from the shore by strong offshore winds; at the same time, water from the depths rises to replace the surface water driven into the sea. Since the water of the depths is colder than the surface waters heated by the sun, as a result of the surge, the water near the shore becomes colder. The surge of water off the Caucasian coast of the Black Sea, caused by a strong northeast wind (this wind is called bora here), can be so powerful that the sea level near the coast can drop by forty centimeters per day.

In the oceans, upwellings arise from the action of the Coriolis force (created by the movement of the Earth around its axis) on masses of water carried by currents in the meridional direction (from the poles to the equator) along the coasts of the continents: the Peruvian current and the Peruvian upwelling (the most powerful in the world) off the Pacific coast of the South America, the Benguela Current and the Benguela Upwelling off the eastern coast of South Africa .

Upwellings lift into the surface, illuminated layer of the ocean (or sea) water enriched with biogenic minerals (salt ions containing nitrogen, phosphorus, silicon), necessary for the growth and reproduction of phytoplankton microalgae - the basis of life in the sea. Therefore, upwelling areas are the most productive water areas - there is more plankton, fish, and everything that lives in the ocean.

Summer holidays on the Black Sea - many Russians dream about this during their working days. However, the southern beaches are fraught with many dangers. Every tourist season, the media reports about people who have died while swimming in shallow waters. The main reason for such accidents is bottom currents. The locals call them tugunami, because these streams of water can easily drag even experienced swimmers to the next world.

What kind of rips and pulls

The strength and speed of the wind have a great influence on the Black Sea currents. Under the influence of storms and other meteorological phenomena, the direction of water flows in this hydrological body changes rapidly.

Group of scientists: A.G. Zatsepin, V.V. Kremenetsky, S.V. Stanichny and V.M. Burdyugov, representing the Moscow Institute of Oceanology named after P.P. Shirshova and the Sevastopol Marine Hydrophysical Institute, wrote a scientific article “Basin circulation and mesoscale dynamics of the Black Sea under wind influence.” This scientific work was published in the collection “Modern problems of the dynamics of the ocean and atmosphere” (Moscow, published in 2010).

The authors of the study noted that depending on the wind, the structure and intensity of the coastal current can repeatedly change from the “jet” to the “wave-vortex” mode of water circulation. And this is confirmed by long-term observational data.

The instability and variability of the Black Sea often leads to the formation of so-called rip currents in the coastal zone. As a result of a storm, waves appear near gently sloping sandy beaches that move not toward the shore, but, on the contrary, away from it. And swimmers caught in such rips or tugs cannot reach land in any way: the current negates all their efforts. In the end, exhausted and panicking people drown in shallow water, very close to the shore.

Such dangerous phenomena occur on many beaches, where the flat bottom is framed by sandbanks and spits. Rips are often found in the Gulf of Mexico, off the Pacific Islands, at Indian resorts, in the Mediterranean, Black and Azov Seas, and residents of the Far East also know about them.

Although the dimensions of the draft are usually small, it reaches 10-15 meters in width and no more than 100 meters in length, the current speed is quite high - up to 3 meters per second. So even a trained swimmer may not be able to cope with such a flow.

Vacationers should be careful. If some section of the sea surface, located near the shore, is noticeably different from the rest of the water area in color and nature of water movement, and white foam has formed on its surface, then it is absolutely forbidden to get into the water in this place.

How do they arise?

Scientists have been arguing about the reasons for the formation of drafts throughout the history of meteorological observations. Most experts believe that it is a matter of wind strength and speed. This point of view is shared, for example, by Natalia Balinets, a hydrologist at the Hydrometeorological Center of the Russian Black Sea Fleet. Her article “Conditions for the occurrence of draft in the ports of the Black Sea” was published in the specialized journal “Ecological safety of coastal and shelf zones and integrated use of shelf resources” (No. 15, 2007).

ON THE. Balinets called the rip current a particularly dangerous hydrometeorological phenomenon. Having analyzed the conditions for the occurrence of drafts over a long period of observation, she determined which atmospheric processes precede them. It turned out that in almost 80% of cases such currents arise as a result of storms formed by Mediterranean cyclones that arrived in the southwestern part of the Black Sea.

But the most powerful drafts arise in the following situation: “Over the northwestern, northern or central regions of the European territory of Russia is the center of a vast cyclone, its trough covers the northern part of the Black Sea. An anticyclone or ridge extends over Turkey or the Balkans. Winds from the south prevail over the sea.”

As N.A. wrote Balinets, in this case the speed of storm winds can reach particular strength, and the water disturbance in some places is fixed at around five points. After such meteorological phenomena, drafts appear in a seemingly calm water area.

Why are they dangerous?

Every year tourists die on the Black Sea. After the start of the swimming season, local authorities and employees of the Russian Ministry of Emergency Situations regularly publish warnings in the media that swimming in certain places after strong storms is prohibited, but vacationers, as a rule, ignore such messages. People don't want to lose long-awaited vacation days, no matter what.

For example, this topic was the subject of a story on the regional TV channel “360,” entitled “Tourists in Anapa ignored the warning about the bottom current. And it is deadly” (release date: July 1, 2019).

The authors of the TV story, Anastasia Kukova and Ekaterina Andronova, talked with the head of the Krasnodar regional hydrometeorological center, Andrei Bondar. The specialist said that the 2019 tourist season is just beginning, and several cases have already been recorded on the beaches of Anapa when vacationers were swept out to sea. And all because people do not pay attention to storm warnings and behave carelessly.

“The wind is quite strong now. On our coast, the current is mainly westerly, and it pushes surface water towards the shore. Therefore, the bottom countercurrent intensifies. If you dive, you may be carried far enough from the shore, and it will be very difficult to swim out,” A.N. warned tourists. Cooper.

How to escape from such a current

Experienced swimmers and rescuers say that people who are caught in a rip current should not panic. The main thing is to soberly assess the current situation.

The author of the daily educational magazine “ShkolaZhizni.ru,” Maxim Selinsky, wrote the article “Rip currents are the main danger for swimmers in the ocean or sea” (publication date: September 7, 2017). It says that it is panic that most often leads to the death of a swimmer who desperately rushes to the shore, losing his last strength and completely exhausted. People should remember that an ordinary draft is only 5-10 meters wide; it is not capable of carrying a person far into the open sea: the rip current, as a rule, completely weakens less than 100 meters from the shore.

“Don't try to fight the current. His speed may be such that even an Olympic swimming champion cannot cope with him. If you find yourself in a reverse current, you should swim not directly towards the shore, but parallel to it, that is, away from the current. In this way you can get out of the trap, after which you can swim towards the shore. Or, realizing that you are being carried away by a rip current, swim at an angle of 45 degrees to the shore and gradually get ashore,” advises Maxim Selinsky.

And of course, you should be careful, do not ignore the warnings of rescuers, and carefully monitor the coastal waters. If in any place the water moves in the opposite direction from the shore, this can be noticed by a change in the color of the wave and white foam (white foam) appearing on the surface.

Currents in the sea can be figuratively compared to rivers without banks. In marine science, it is customary to designate the direction of currents using the “where” principle. Unlike currents, wind and wave directions are determined by the “from” principle. For example, a wind blowing from south to north will be called south, and the current created by this wind will be called north.

Map of Black Sea currents

The currents of the Black Sea are weak, their speed rarely exceeds 0.5 meters per second, their main causes are river flow and the influence of winds. Under the influence of river flow, the water should move towards the center of the sea, but under the influence of the force of the Earth's rotation, it deviates to the right (in the northern hemisphere) by 90 degrees and flows along the coast in a counterclockwise direction. The main stream of currents has a width of 40-60 kilometers and passes at a distance of 3-7 kilometers from the coast.

Separate gyres are formed in the bays, directed clockwise, their speed reaches 0.5 meters per second.
In the central part of the sea there is a calm zone, where the currents are weaker than off the coast and are not constant in direction. Some researchers identify two separate rings in the general flow. The origin of the two rings of currents is associated with the peculiarities of the outlines of the Black Sea, which contribute to the deviation of parts of the general flow to the left off the coast of Crimea and Turkey.

An interesting system of currents is observed in the Bosphorus Strait; it is of great importance for the Black Sea.

These currents were first studied at the end of the last century by Admiral Makarov. S. O. Makarov was not only an outstanding naval commander, shipbuilder, and military theorist, he was also a remarkable scientist who understood how important it is to understand the environment in which the navy has to operate.

From conversations with local residents, S. O. Makarov established that there are two currents in the Bosphorus: surface and deep. He tested this fact by successively lowering a load into the water to different depths. The load was secured by a cable to a buoy floating on the surface. When the load was in the surface layers, the buoy moved towards the Sea of ​​Marmara; when the load was at the bottom, the buoy was carried towards the Black Sea. Thus, it was established that the surface current, carrying desalinated water, goes to the Sea of ​​Marmara, and the deep one, carrying denser salty water, goes to the Black Sea. S. O. Makarov established that the speed of the upper current is 1.5 meters per second, the lower one is 0.75 meters per second; The depth of the current interface is 20 meters. The lower current does not go strictly under the upper one, both of them are reflected from the capes, sometimes the current jets bifurcate.

To explain the reasons for these currents, Makarov performed the following experiment. Water was poured into a glass box, divided into two parts: salted in one part, desalinated in the other. Two holes were made in the partition, one above the other. Salt water began to move through the lower hole, desalinated water through the top. S. O. Makarov was the first to explain the origin of these two layers. The upper current is a waste stream; it is formed under the influence of excess water brought by rivers to the Black Sea. The lower one, the so-called dense one, is formed as a result of the fact that the denser waters of the Sea of ​​Marmara exert greater pressure on the underlying layers than the lighter waters of the Black Sea. This causes water to move from an area of ​​higher pressure to an area of ​​lower pressure.