Movement of water in bays scanword. Non-periodic flows
Chapter 5. Dynamic regime of the World Ocean 73
3. In narrow rocky shores (the gates of the large closed Avachinskaya bays in Kamchatka and Vladivostok) tsunamis break on the rocky shores, losing their energy. Inside such bays there is a slight rise in water, which does not pose a serious danger (Fig. 17).
Therefore, when notified of an approaching tsunami, many sea vessels take refuge in Avachinskaya or Vladivostok bays. There are such bays off the coast of the USA and Canada.
Tsunami prediction and warning . Over the course of many centuries, residents of coastal states have accumulated experience with information about the approach of a tsunami.
1. 10-40 minutes before the appearance of this terrible wave, a retreat (retraction) of water occurs, i.e., exposure of several tens and sometimes hundreds of meters of the oceanic coastal zone of the bottom.
2. Shortly before the sea water recedes, an oppressive silence reigns over the ocean, replacing the noise or groan of the surf.
3. Domestic animals - cats, dogs, horses, etc. - react very actively to the approach of a tsunami, and wild animals - weasels, rats, mice, gophers, snakes. You can also observe the unexpected behavior of birds (the cries of pheasants, many birds fly away from the shore).
4. Instruments (seaographs) monitor the approach of a tsunami.
 Over the past decades, a constant exchange of information on tsunami prevention has been established between scientists from the USA, Russia, and Japan. The International Center for Information on the Origin and Propagation of Tsunamis is located in Honolulu (Hawaii Islands). Since 1975, international warning communications have been established along the Honolulu - Tokyo - Khabarovsk line.
Tsunami waves can be caused not only by earthquakes
è volcanic eruptions, but also typhoons, cyclones, hurricanes. True, in these cases they are called not the word “tsunami”, but “pressure waves”, i.e. waves caused by deep and sudden changes in atmospheric pressure. The coasts of the Atlantic Ocean especially suffer from such waves - Bristol Bay in the North Sea, the mouth of the Thames River; within the Baltic Sea - the Gulf of Finland. Such tsunamis here are called solitons. They do not propagate in the form of a series of waves, but in the form one and only (soloing), i.e. soliton. Most of them are caused by cyclones. If a cyclone settles for a long time over a significant area of the sea
74 Chapter 5. Dynamic regime of the World Ocean
surface and is accompanied by heavy precipitation, then it manages to cause a noticeable rise (swelling) of the sea surface. This is also facilitated by winds that drive water towards the center of the cyclone. Solitons often stagnate in the North and Baltic seas, as a result of which low pressure is established here for a long time, and constant rains cause swelling and a rise (by 80 cm) of the sea surface around the cyclonic center. As a result of a sudden change in atmospheric pressure, accompanied by strong gusty winds from the west, the soliton rushes east. “Soliton” waves are responsible for the famous floods in Bristol Bay in London (Great Britain) and St. Petersburg (Russia).
Solitons are single waves formed over the sea surface, where cyclonic weather with constant rain sets in for a long time.
Seiches. Often in the seas there are fluctuations in surface level, covering the entire sea as a whole. These oscillations resemble standing waves of enormous length, with characteristic “knots”. The amplitude of such standing waves can reach several meters. Such waves are called seiches (French seiche, which means free vibrations, or from the Latin siccus - dry). Seiches are formed in closed bodies of water (seas, bays, bays, lakes). They represent oscillatory movements of the entire mass of water without the propagation of a wave profile over the surface, as a result of which special periodic fluctuations in level are observed near the coast, imperceptible to the eye. The term “seiches” has been used for two centuries to describe the rise and fall of water that occurs periodically in the narrow part of Lake Geneva, where the genesis of this phenomenon was studied at the end of the 19th century by the Swiss scientist Forel. He established that seiches in their elementary form are due to two long waves propagating simultaneously in opposite directions. As a result, instead of two waves, a “standing wave” appears, which looks like this: if at one end of the lake (bay) there is low tide, then at the other there is high tide.
Between these extreme positions, the lake level does not change during the entire cycle of fluctuations. A line (vertical section) across the entire width of the lake, on which there is no vertical movement of the surface, is called a nodal line, and a seiche is called a one-node, if one node is observed
Chapter 5. Dynamic regime of the World Ocean 75
the entire length of the lake; if there are two nodes - a two-node, the other nodes - a three-node, etc. Usually, seiches, due to the impressive size of reservoirs, have rather long periods of oscillation, but sometimes this period is only a few minutes, then seiches begin to create certain problems in seaports . For example, in Los Angeles Bay (USA), wave oscillations occur with periods ranging from 12 to 2-3 minutes. Such high-frequency vibrations are no longer seiches, but are called tyagun. The horizontal movements of water particles during drafting can reach several meters, and the resulting waves are so strong that invisible underwater waves tear steel cables, tear ships from strong anchor chains, and hit the ship against the pier. And there are cases when ships, even with seemingly calm seas and clear weather, perish in port. Having small vertical displacements of water, the draft is practically invisible. You can only escape from it on the open sea. Despite long-term research, the reason for the formation of tyagun has not yet been clarified.
The main reasons causing the formation of a seiche are: a sharp change in atmospheric pressure; sudden strong wind; heavy rain, snow or hail over the surface of the water basin; rapid change in atmospheric pressure as a result of the cessation of a squall; flood flows from rivers; fundamental disturbances of the sea bed during strong earthquakes, etc.
 within large expanses of water (seas, bays), the formation of seiches is influenced by the rotational motion of the Earth and Coriolis forces. But this factor does not have a significant impact on the formation of seiches in small water basins.
 in our textbook there is a need to dwell on the characteristics special waves.
bore - a deformed tidal wave observed in the conditions of some rivers and estuaries . It appears in the form of a single long wave with a breaking crest and a high propagation speed (10 m/s). The height of this wave is not less than 2-6 m and represents a high water shaft, the front side of which resembles a moving water wall. As a rule, the frontal attack of the wave goes along the entire perimeter of the river to the very bottom. These waves have different names in different parts of the world. On the Atlantic coast of France (the mouth of the Seine River) - this phenomenon is called “ìà-
76 Chapter 5. Dynamic regime of the World Ocean
scare” - height 1.5 m. At the mouth of the Congo (Africa) this wave is called “kalema” - height 1.5-2 m. It is timed to coincide with the period of zenithal rains. The strongest bore is observed on the Fuchunjiang River in China, the height of the wave is up to 6-7 m. On the Ganges River, this phenomenon is called bore - height up to 2 m. In the classical form, a deformed tidal wave bore is presented at the mouth of the Amazon River. In the Tupi language this wave is called pororoka, which means “thundering water.” Many residents call it amazunu, which means “boat wrecker,” which may be where the name of the river itself comes from. Pororoka comes from the Atlantic Ocean, starts in shallow water and rushes with enormous force and speed across the entire width of the river against its current, forming a wave 4-6 m high, carrying fresh water and not mixing with the salty waters of the ocean. Pororoka goes a thousand kilometers deep into the mainland, floods low banks, crushing and destroying tens of meters of coastal soil and uprooting thousands of centuries-old trees of the Amazon forest. This phenomenon is accompanied by a loud roar that can be heard for tens of kilometers around. The speed of the wave shaft reaches 10 m/s. Amazunu (pororoka) spreads across the entire width of the river (10-30 km), reaching the bottom (70 m). On its way, the wave carries billions of tons of soil, destroying everything, and presents a terrible sight. Pororoka (amazunu) is active in February-March-April and is usually timed to coincide with the full moon, but lasts no more than 30 minutes and lays eggs.
Storm centers in the World Ocean. Modern advances in the study of the regime functions of ocean waves have made it possible to identify a number of storm centers within the World Ocean, where wind waves reach significant heights. Due to the presence of vast water areas in the Southern Hemisphere, within which the wind can influence the ocean surface for a long time, the Antarctic region
The region of the Southern Hemisphere is the main source of storm disturbances. At 40-60 south. w. almost always there is no
how many areas of storm surge moving in an easterly or southeasterly direction at a speed of about 40 km/h. But the strength and direction of the winds over this vast area are very stable over time. Mode waves here have a latitudinal distribution. Storm waves reach their greatest values not near the “roaring” 40’s latitudes, but
Chapter 5. Dynamic regime of the World Ocean 77
near 50-60 S. w. in the Atlantic, Pacific, Indian and Southern oceans. In the western air transport zone of the Antarctic region, 5 wave centers are distinguished.
1. Within the Indian (and now Southern Ocean with a center near O. Kerguelen) is the stormiest region of the World Ocean. In all seasons of the year, the highest wind wave heights (up to 35 m) are observed here.
2. The second area of increased storm activity is located between New Zealand and Antarctica, in the vicinity of Macquarie and Emeralda Islands. The area of this region is much smaller than the Kerguelen region. In the New Zealand storm center, average wave heights are constant and amount to 2-3 m, and maximum - 20-25 m.
3. The third place in terms of storm activity is occupied by the storm center in the Drake Passage, where wave heights are up to 20 m. During the sailing fleet, this was the most dangerous area for sea navigation.
4. The fourth storm center is located northeast of the South Sandwich Islands, where maximum waves reach 15-20 m.
5. Increased storm activity is also observed
â Southern Ocean, in the area from 100 to 140th meridian. Moderate waves are 5-6 m high, and maximum wave heights in the center of the area exceed 15 m.
Thus, all five storm centers of the Southern Hemisphere are located in the zone of westerly air transport and are areas of the most intense transfer of atmospheric energy to the ocean surface.
In the Northern Hemisphere, five more storm centers can be identified. The stormiest areas here are the temperate latitudes of the Pacific and Atlantic oceans.
1. A powerful storm center is located in the Pacific Ocean, near North America at the mouth of the Columbia River (Cape Disappointment). The stormiest waves arise here, reaching from 4 to 10 m in height. The US Pacific Coast Rescue Service is located in this area.
2. Near the American continent in the temperate latitudes of the Atlantic, near Sable Island, there is the most powerful storm center in the Northern Hemisphere, where wind wave heights reach 15 m.
Chapter 5. Dynamic regime of the World Ocean 79
3. Another center is located in the waters of the Bay of Biscay, where the waves reach 6-8 m, and sometimes 12-15 m. This center is sometimes called Galician.
4. The formation of the Arabian storm center is associated with the development of a strong summer monsoon. The wave height reaches 8 m.
5. The presence of a storm center within the Bay of Bengal is associated not only with the monsoon circulation, but also with the cyclonic activity characteristic of this part of the Indian Ocean. Here the wave height reaches 10 m, which made it very difficult to sail to India and around Africa during the great geographical discoveries.
5.2. SEA (OCEAN) CURRENTS
Main currents. Marine (ocean) or simply currents are the translational movements of water masses in the oceans and seas over distances measured in hundreds and thousands of kilometers, caused by various forces (gravitational, frictional, tidal) (Fig. 18). Sea currents play a huge role in the life of the World Ocean, in navigation, they contribute to the exchange of water masses, changes in coastlines, as well as climate in different parts of the globe, etc.
The presence of sea currents is a characteristic feature of ocean waters. Even in ancient times, people established that the wind blowing over the sea causes not only waves, but also currents, which play a huge role in the process of heat redistribution on Earth, and they showed special interest in studying them.
We find the first mentions of currents among the ancient Greeks. Aristotle described currents in the Kerch straits,
REGION 18. The main surface currents of the World Ocean.
1 – Gulf Stream; 2 – North Atlantic; 3 – Norwegian; 4 – North Cape; 5 – Spitsbergen; 6 – East Greenland; 7 – West Greenland; 8 – Labrador; 9 – Canary; 10 – Northern Trade Winds; 11 – Guiana; 12 – equatorial countercurrents; 13 – Southern Trade Winds; 14 – Brazilian; 15 – Benguela; 16 – Falkland; 17 – Antarctic circumpolar; 18 – Madagascar; 19 – Mozambican; 20 – Cape Agulhas; 21 – Somali; 22 – monsoon (summer); 23 – Western Australian; 24 – Peruvian; 25 – East Australian; 26 – Kuroshio; 27 – North Pacific; 28 – Àëÿ-
Skinskoe; 29 – Kuril; 30 – Californian; 31 – Transantarctic
80 Chapter 5. Dynamic regime of the World Ocean
Bosphorus, Dardanelles. Theofastus mentions the current in the Strait of Gibraltar. The inhabitants of Carthage knew about the currents in the Atlantic Ocean. Knowledge about the existence of currents made it possible for Scandinavian sailors (Normans, or Vikings) back in the 9th-10th centuries to overcome fear and enter the waters of the North Atlantic, colonize Iceland, the southern parts of Greenland and the coast of North America, calling it Vinland, as evidenced by references in the Scandinavian sagas Observations of currents in the open ocean were carried out by H. Columbus during his first voyage to America. In the 19th-20th centuries, the currents were studied by many expeditions around the world. As a result of the accumulated information, we can say that currents are complex combinations of various types of non-periodic and periodic movements of water. Current directions vary in degrees and indicate where does the water flow?(as opposed to the direction of the wind, which indicates where it is blowing from). Current speed is measured in meters per second or in knots (1 knot = 0.5144 m/s).
At one time, the outstanding Russian climatologist A.I. Voeikov called sea currents “water heating pipes” of the globe. Enormous masses of water move among the oceans and, depending on where they begin, carry with them heat or cold.
Warm waters in the western parts of the oceans are directed, as a rule, to the poles and, like a water heating system, heat the high latitudes, and in the east they return cooled to the equator. Essentially, currents play the role of a planetary energy “damper.” Thus, ocean currents are truly grandiose natural phenomena. The most powerful and most famous sea current is the Gulf Stream - a kind of giant river in the ocean, which begins in the southern latitudes, passes through the Caribbean Sea, the Straits of Florida (at a speed of 7-9 km/h), crosses the Atlantic Ocean and reaches the islands Spitsbergen and Novaya Zemlya, extending over 10,000 km (Fig. 19). The reason for its origin is a large surge of water mass by trade winds through the Yucatan Strait into the Gulf of Mexico. When entering the ocean, the power of the current is 25 million m/s, which is 20 times greater than the flow of all rivers on the globe. The width of the current is 75-120 km, the vertical thickness of the flow at depth is 700-800 m. The waters of this current carry a colossal amount
Chapter 5. Dynamic regime of the World Ocean 81
RICE. 19. Gulf Stream Current
heat that warms the whole of Western and Northern Europe. The influence of the Gulf Stream greatly affects the nature of the Arctic Ocean. Thanks to the Gulf Stream, the northern coast of Europe is much warmer than at the same latitudes of North America. In England, for example, evergreen plants grow (rhododendron, holly, strawberry tree), and the northernmost of the Lofoten Islands, located near the Arctic Circle, has the average annual temperature of the Crimean Peninsula. The role of the same stove for the Japanese islands is played by the Kuroshio Current in the Pacific Ocean. It also begins in the equatorial latitudes, rushes to the north, and near the Japanese Islands it turns to the northeast and goes to Alaska, forming the climate of “eternal autumn” there. Kuroshio has a width of 180 to 230 km, and the depth of its waters is 600 m. In the northwest of the Pacific Ocean there is a cold Oyashio (Kuril) current, running from north to south along the eastern shores of the Kuril ridge and Hokkaido Islands.
Along with warm currents, there are cold ones. From Baffin Bay, through Davis Strait to the Atlantic
82 Chapter 5. Dynamic regime of the World Ocean
The cold Labrador Current rushes into the ocean, carrying there cold waters with a temperature difference of 8-10, with the presence of numerous icebergs carried out from the polar latitudes. One of these icebergs was the cause of the sinking of the Titanic in 1912. The presence of the Labrador Current forms a tundra zone in eastern North America at latitude 55 (latitude of Minsk), and a natural zone of steppes and deciduous forests at latitude 50 (latitude of Kiev).
 In the tropical latitudes of the Pacific Ocean, off the coast of South America, the cold surface Peruvian Current (Humboldt Current) passes, which has a great influence on atmospheric processes in this area. Air masses, passing over the cold waters of the current, are not saturated with moisture and do not bring precipitation to the mainland. Therefore, the coast and western slopes of the Andes do not receive precipitation for many years in a row. The cold waters of the Peruvian Current, rich in oxygen and nutrients, are very rich in organic life. Here is the largest fishery for one species of anchovy, thanks to which Peru catches 7-10 million tons of fish resources.
Since the time of H. Columbus, it has been known that trade winds in the tropics excite powerful trade wind currents, and between the northern and southern trade winds there is a strip of calms and weak winds. In the zone of weak winds, the Equatorial, or Intertrade-wind, countercurrent is found, moving towards its two neighbors in the north and south. Such a system of currents and countercurrents exists in all oceans, but each with its own characteristics.
 In the Pacific Ocean, the countercurrent originates near the Philippines and moves due east, just north of the equator, between two trade wind currents.
 In the Indian Ocean, the system of equatorial currents is shifted south of the equator and is strongly influenced by monsoon winds. Continuing the northern winter(December-January), when the northeast monsoon blows, trade wind currents and countercurrents form here. Only the Somali Current (similar to the Gulf Stream and Kuroshio) behaves unusually, moving south in a wide strip. In the summer (July-August), when the southwest monsoon predominates, the Equatorial Countercurrent disappears, and the Somali Current flows north in a narrow stream, faster than the Gulf Stream.
Tidal fluctuations in ocean level are accompanied by horizontal movement of water masses, which is called the tidal current. Therefore, the navigator must take into account not only changes in depths, but also the tidal current, which can reach significant speeds. In areas where there are high tides, the boatmaster must always be aware of the height of the tide and the elements of the tidal current.
Tides allow deep-draft ships to enter some ports located in shallow bays and estuaries.
In some places, the tides are intensified by surge phenomena, which leads to a significant increase or decrease in the level, and this in turn can lead to accidents of ships under cargo operations at berths or in the roadstead.
The nature and magnitude of tides in the World Ocean are very diverse and complex. The magnitude of the tide in the ocean does not exceed 1 m. In coastal areas, due to the decrease in depth and the complexity of the bottom topography, the nature of the tides changes significantly compared to tides in the open ocean. Along straight shores and capes protruding into the ocean, the tide fluctuates within 2-3 m; in the coastal part of the bays and with a heavily indented coastline, it reaches 16 m or more.
For example, in Penzhinskaya Bay (Sea of Okhotsk) the tide reaches 13 m. On the Soviet shores of the Sea of Japan its height does not exceed 2.5 m.
In the seas, the height of the tide depends on what kind of connection a given sea has with the ocean. If the sea extends far into the land and has a narrow and shallow strait with the ocean, then the tides in it are usually small.
In the Baltic Sea, tides are so small that they are measured in centimeters. The tide height in Calais is 7 cm, in the Gulf of Finland and Bothnia about 14 cm, and in Leningrad about 5 cm.
In the Black and Caspian Seas, the tides are almost imperceptible.
In the Barents Sea, tides are semi-diurnal.
In the Kola Bay they reach 4 m, and near the Iokan Islands - up to 6 m.
In the White Sea the tides are semi-diurnal. The highest tide height is observed on the Tersky coast in the throat of the sea, where at the Oryol lighthouse it reaches 8.5 m, and in the Mezen Bay - up to 12 m. In other areas of this sea, the tides are much lower; So, in Arkhangelsk it is about 1 m, in Kemi - 1.5 m, and in Kandalaksha - 2.3 m.
A tidal wave, penetrating into the mouths of rivers, contributes to fluctuations in their levels, and also significantly affects the speed of water flow in the mouths. Thus, often the speed of the tidal current, dominating the speed of the river, changes the flow of the river to the opposite direction.
Winds have a significant influence on tidal phenomena.
A comprehensive study and accounting of tidal phenomena is of great importance for the safety of navigation.
The current that is directed in the direction of the movement of the tidal wave is called tidal, the opposite is called ebb.
The speed of tidal currents is directly proportional to the magnitude of the tide. Consequently, for a certain point, the speed of tidal currents at syzygy will be significantly greater than the speed at quadrature.
With increasing declination of the Moon, as well as as the Moon moves from apogee to perigee, the speed of tidal currents increases.
Tidal currents differ from all other currents in that they capture the entire thickness of water masses from the surface to the bottom, only slightly reducing their speed in the near-bottom layers.
In straits, narrow bays and near the coast, tidal currents have the opposite (reversible) character, that is, the tidal current is constantly directed in one direction, and the ebb current has a direction directly opposite to the tidal one.
In the open sea, far from the coast, and in the middle parts of fairly wide bays, there is no sharp change in the direction of the tidal current to the opposite direction, i.e., the so-called change of currents.
In these places, a continuous change in current directions is most often observed, and a 360° change in current occurs with a semi-diurnal tide in 12 hours and 25 minutes and with a diurnal tide in 24 hours and 50 minutes. Such flows are called rotating flows. Changes in the directions of rotating currents in the northern hemisphere, as a rule, occur clockwise, and in the southern hemisphere, counterclockwise.
The change from tidal current to ebb current and vice versa occurs both at the moment of high and low waters, and at the moment of average level standing. Often, a change in currents occurs in the period of time between high and low water. When the tidal current changes to ebb and flow, the current speed is zero.
The general pattern of tidal currents is often disrupted by local conditions. Taking into account the tidal current, as mentioned above, is of great importance for the safety of navigation.
Data on the elements of tidal currents are selected from the Atlas of Tidal Currents, and for some areas of the seas - from tables located on navigation charts. General instructions about currents are also given in sea directions.
Relatively constant currents are shown on maps with arrows. The direction of each arrow corresponds to the direction of the current operating at a given location, and the numbers above the arrow indicate the speed of the current in knots.
The direction and speed of tidal currents are variable quantities, and in order to reflect them on the map with sufficient completeness, you need not one arrow, but a system of arrows - a vector diagram.
Despite the clarity of vector diagrams, they overload the map and make it difficult to read. To avoid this, elements of tidal currents are usually shown on the map in the form of tables placed in free spaces on the map. A complete table is a table that contains the following data:
Watch relative high water at the nearest tidal point; the inscription “Full water”, corresponding to zero hours, is placed on
In the middle of the column, from it up, in ascending order, are the digits of the hours until full water, and downwards, also in ascending order, are the digits of the hours after full water;
Geographic coordinates of points, usually designated by the letters A; B; IN; G, etc. ; the same letters are placed in the corresponding places on the map;
Elements of currents: direction in degrees and speed in syzygy and quadrature in knots (with an accuracy of 0.1 knots).
The determination of the speed and direction of the current at a given moment in a given place according to the Atlas is found as follows.
First, the main port for a given place is determined using the Atlas, after which, using the Tide Table (Part I), the time of high water closest to the given one is found, and the time interval (in hours) before or after the moment of high water in the main port relative to the given moment is calculated. Then, for the calculated period of time before or after the moment of high water, the direction of the current (in degrees) and speed (in knots) are found in the Atlas.
When sailing, the elements of tidal currents must be determined in advance; It is recommended to compile a table of currents for pre-calculated moments (after 1 hour) corresponding to the ship’s countable positions.
Below is an example of a table of tidal currents (Table 7).
The oscillatory movements of the entire mass of water in a reservoir or lake are called seiches. At the same time, the surface of the water acquires a slope in one direction or the other. The axis around which the surface of the reservoir oscillates is called the seiche node. Seiches can be single-node (Fig. 40, And), two-node (Fig. 40, b) etc.
Rice. 40. Seiches
Seiches occur during sudden changes in atmospheric pressure, the passage of a thunderstorm, or sudden changes in the strength and direction of wind that can shake a mass of water. The water mass, trying to return to its previous equilibrium position, begins to oscillate. Vibrations under the influence of friction will gradually fade. The trajectories of water particles in seiches are similar to those observed in standing waves.
Most often, seiches have a height of several centimeters to a meter. The periods of seiche oscillations can range from several minutes to 20 hours or more. For example, in the near-dam part of the Tsimlyansk Reservoir, single-node seiches are observed with a period of 2 hours and a height of 5-8 cm.
Tyagun is a resonant wave vibration of water in ports, bays and harbors, causing cyclic horizontal movements of ships moored at the berths. The period of water oscillations during draft is from 0.5 to 4.0 min.
The drafts create long-period standing waves where water particles move in the orbits of the nodes. However, below the top and bottom of the wave, their movement is directed vertically. The period of oscillation of the water surface and the speed of movement of particles depend mainly on the configuration of the shores and the depth of the basin.
The port is not a completely closed basin; it communicates with an open body of water or the sea through a relatively narrow passage. Any vibration of water in this passage under the influence of external forces causes its own vibrations of the water in the pool. External forces can be:
post-storm long-period swell; pressure waves that arise after a rapid exit of a cyclone and anticyclone from the sea to land;
internal waves formed under the influence of storms in the open sea or lake, which, approaching shallow water, come to the surface and penetrate into the port water area. If the period of the external force is close to the period of natural oscillations of the port water area, then these oscillations quickly increase and reach their greatest magnitude. After the cessation of external forces, the oscillations die out.
Depending on where the ship is on the thruster, it experiences either horizontal or vertical movements. If the dimensions of the vessel and the mooring points are such that the period of its own oscillations is close to or coincides with the period of the seiches, then strong resonant movements occur. Moreover, there may be a ship nearby that practically does not experience the action of the thruster, since it differs from the first one in size, weight, periods of pitching and natural oscillations.
During drafts, passenger ships are forced to leave for the roadstead, since parking at the berths becomes impossible, and cargo ships are forced to stop working. Even with very small accelerations, shock forces arise in the movement of the vessel that can damage its hull. Thrusts affect ships differently, so navigators must know their characteristics in a given port, the period of water fluctuations in the water area, as well as the peculiarities of the behavior of their vessel during heavy drafts.
When the volume of water changes (inflow and flow), as well as when the water mass moves in lakes, fluctuations in water levels occur. The greater the change in water volume, the greater the amplitude of water level fluctuations (it can be from 2-3 cm to several meters).
The magnitude of level fluctuations largely depends on the area and nature of the shores of the lake. During the year, in individual climatic zones, periods of level fluctuations are different. In northern latitudes, the greatest fluctuations occur at the beginning of summer and the smallest at the end of spring. In the north-west of the European part of the USSR, during the year, maximum levels occur in spring and autumn and minimum levels in winter and summer. In lakes in the central part of Siberia (for example, on Baikal), the highest level occurs in the summer, and the lowest in autumn, winter and spring.
The phrase in the title is a literal translation of the Japanese word “tsunami” and refers to a unique natural phenomenon: several successive long ocean waves generated by sharp displacements of large areas of the ocean floor caused by earthquakes.
Tsunamis formed at great depths are a transverse long wave (100-300 kilometers long) of low height (no more than 2 meters), propagating at a speed of about 0.2 kilometers per second (700 kilometers per hour), their period is 15-60 minutes . But when they reach shallow water, these waves sharply increase in height, their length decreases, the crests begin to collapse and, in essence, huge waves of movement are formed, to which the name “tsunami” actually refers. In some cases, the wave height reaches 30-40 meters.
The arrival of a tsunami on the coast is usually preceded by a drop in sea level and the arrival of relatively small waves. Then there may be a secondary drop in level, and after that a tsunami comes. After the first wave, as a rule, several more waves of larger magnitude come at intervals from 15 minutes to 1-2 hours. Usually the third or fourth wave is the maximum.
The waves penetrate deep into the land, depending on its topography, sometimes 10-15 kilometers and, having high speed, cause enormous destruction. After receiving a tsunami warning, it is necessary to take the ship out to the open sea to meet the wave.
In coastal areas, there are frequent cases of the formation of another natural phenomenon - large standing waves - suloya, which means a whirlpool, a crush. Small suloi are observed in the Black Sea (in the Kerch Strait), stronger ones - in the narrows off the Pacific coast of Canada and the skerries of Scandinavia. But suloi reach their largest sizes in shallow water areas with strong reverse currents - in the Kuril Straits, Singapore Straits, Portland Firth, etc. (up to 4 meters). The formation of ripples is usually associated with the interaction of two counter flows of water (Fig. 4.36a.). In this case, vortices are formed in the frontal zone, emerging to the surface in the form of random waves, and the higher the flow speed, the greater the energy of these waves.
Suloi can also appear as a result of a flow entering shallow water. In this case, large velocity gradients are formed in the water stream, flow discontinuities, vortices and, as a consequence, waves on the surface (Fig. 4.36b).
The ripples reach their greatest size during the maximum speeds of tidal currents. This dependence of suloi on the nature of the tide allows them to be predicted very reliably.
Suloi is very dangerous for navigation. Vessels passing through the swell experience unpleasant, disorderly rolling, go off course, and a high wave can tear off mechanisms and life-saving equipment from their fastenings. Crossing such areas by small vessels threatens them with death.
When water in the sea has a jump in density at any depth, waves called internal waves can arise at the boundary between the upper less dense layer and the lower layer with a sharply increased density.
Internal waves can have a height several times greater than surface waves (up to 90 m, period up to 8 minutes).
When internal waves are excited, a phenomenon known as “dead water” is observed.
A ship in dead water loses speed and can remain almost in place when the machinery is fully operational.
When following “dead water” in a calm state, the surface of the sea takes on an unusual appearance. Transverse waves increase greatly behind the stern, and a huge wave appears in front of the ship, which the ship is forced to push. On “dead water”, almost the same wave movements occur as when a ship moves through shallow water. If the speed of the ship coincides with the speed of propagation of free internal waves, then during its movement the ship creates not only ordinary ship waves on the surface of the water, but also generates waves at the interface of two layers - the “light” upper and “heavy” lower ones. The wave occurs when the interface layer is located approximately at the depth of the keel. In this case, the water masses of the upper layer, with a thickness equal to the ship’s draft, move in the opposite direction and cause a loss of speed of the ship; wave resistance increases greatly, since the ship has to “drag along” the suddenly arisen wave. This phenomenon explains “dead water”.
The phenomenon of “dead water” occurs everywhere near the mouths of large rivers - the Amazon, Orinoco, Mississippi, Lena, Yenisei, etc. But it is especially often observed in Norwegian fiords and in the Arctic seas in calm spring weather during ice melting, when there is a relatively thin layer of almost fresh water located above highly saline and dense sea water.
Internal waves pose a serious threat to underwater navigation. This is manifested both in the direct, physical impact of internal waves, internal surf on submarines, and indirectly - the complication of the conditions for the passage of sound in water.
An in-depth study of the structure of large ocean currents has revealed that these flows are far from being a “river with liquid banks,” as previously thought. It turned out that the currents consist of a number of alternating jets moving at different speeds. Moreover, a speed of 2.7 m/s (5.2 knots) was measured in the Gulf Stream. In addition, it was discovered that there are narrow countercurrents on both sides of the main flow (can reach 2 knots).
Another interesting feature of currents was revealed: streams bend in space, forming bends - like river meanders. Meanders, increasing in size, move with the current, and sometimes break away from it and move independently. The separated meanders form vortices of various sizes. To the left of the general flow, the vortices rotate clockwise, to the right - counterclockwise. The current speed in these eddies is up to 2.0 knots.
Observations have shown that, for example, in the Gulf Stream field, 5-8 pairs of cyclones and anticyclones are formed per year. The most developed Gulf Stream cyclones have a diameter of up to 200 km and capture a layer of water masses almost to the ocean floor (2500-3000 m). Gulf Stream cyclones drift generally to the southwest at speeds of up to 3 miles per day.
The discovery of vortices is of great importance for navigation in the open ocean. The vortex circulation system is the real field of currents that affects a ship located in the ocean. When passing through areas with constant currents marked on hydrometeorological maps and atlases, navigators should be aware that the real variability of current directions and speeds, and therefore the actual drift of the vessel, can differ greatly from the directional direction of the current.
Many navigators have noted that often, especially in tropical latitudes, at night, the glow of water flowing onto the bow of the ship is clearly visible; The seething water at the sides glows, flowing around the hull; a swirling, gradually narrowing and fading light strip forms behind the stern. The glow of the water highlights the shore, rocks, reefs, shallows, buoys, ships and jetties against the general background of the sea.
As hydrobiologists have found out, the glow of the sea is caused mainly by the bioluminescence of marine organisms. The most common is the sparkling or flickering glow of various unicellular and multicellular plankton creatures ranging in size from tens of microns to several millimeters. When there are many such luminous beings, individual points of light merge into an uneven glow. This glow occurs when organisms are mechanically irritated, for example, when animals and fish move, when an oar hits the water, and also when exposed to chemicals.
For a long time, sailors returning from the tropical seas of Southeast Asia spoke of encountering gigantic luminous wheels, several miles in diameter, rotating at high speed on the surface of the sea. Western European sailors dubbed them the “devil’s carousel”; in the East they are called “Buddha wheels”.
The formation of small-scale vortices can be considered an explanation for these phenomena. Such vortices and whirlpools arise at the edges of currents, at the junction of differently directed flows of any origin, where the depth is shallow, tidal currents are strong and internal waves arise.
Falling winds
The general name “falling winds” includes coastal winds observed in the foothills of some seas; These winds are called differently in different areas: foen, bora, mistral, sarma. They are united by such qualities as surprise, great force and the nature of the impact on ships. Many ships suffered accidents during bora near the Novaya Zemlya coast, off the coast of Greenland, and in the roadsteads of such large ports as Trieste, Marseille, and Novorossiysk.
The speed of falling winds reaches 40 meters per second at the sea surface, and with gusts 50-60. Naturally, they pose a great danger to coastal navigation, to the mooring of ships in roadsteads and at berths, and to the operation of ports.
When studying this phenomenon, researchers noticed that bora usually occurs in winter, and in those areas where coastal mountains border a fairly high plain, which becomes very cold in winter. A high pressure area often forms over the plain, while a cyclonic area persists over the sea. This creates large horizontal gradients that move huge masses of cold air. Due to the action of gravity, the speed of air movement increases sharply as it passes over the ridge.
The rapid fall of cold air onto the surface of the bays creates strong waves in the coastal zone; at subzero temperatures, water splashes cause icing of ships and port facilities. Ice armor reaches up to 4 meters, which often causes catastrophic consequences. Vertically, the bora extends to 200-300 meters, and horizontally - only a few miles from the coast.
The mechanism of hair dryer formation is slightly different. The proper name of the wind “fen” (warm) gives the key to understanding the nature of the phenomenon. It has been established that the foehn is formed due to a significant difference between atmospheric pressure inland and over the sea. When a cyclone passes over the sea near the coast, when a high-pressure core remains inland, the pressure field forms flows of air masses directed from the land to the sea. And if there are mountains on the path of these flows, then masses of air, accumulating behind the ridge, begin to slowly rise. As the air rises, the air temperature drops, and the humidity gradually increases and reaches a maximum at a certain point.
At the top of the ridge, where the air is supersaturated with water vapor, it begins to condense, forming a cloud bank that covers the entire mountain range - a characteristic “foehn wall” appears. From this height, the air rushes to the sea, heating up, so it arrives at the coast with a higher temperature and low humidity.
Sometimes, under appropriate weather conditions, small-scale atmospheric vortices are formed - tornadoes (or as they are sometimes called - tornadoes, blood clots, typhons).
An ordinary tornado is formed as follows: as a result of intense ascending air currents, the edge of a formidable cloud begins to rise, twisting horizontally around an axis parallel to the cloud boundary - a small rotor is formed. The rotor, rotating rapidly, lowers one end (usually the left one according to the movement of the cloud) to the ground in the form of a funnel. This funnel - the main component of a tornado - is a spiral vortex consisting of extremely rapidly rotating air.
The internal cavity of the funnel, with a diameter ranging from several meters to several hundred meters, is a space limited by walls; it is almost clear, cloudless, sometimes small lightning flashes from wall to wall; the air movement in it weakens. The pressure here drops sharply - sometimes by 180-200 mb. Such a catastrophically rapid drop in pressure causes a peculiar effect; Hollow objects, in particular houses, other buildings, car tires, explode when they come into contact with a tornado funnel.
There are no direct measurements of wind speed in tornadoes: not a single device can withstand enormous accelerations. However, experts in the strength of materials calculated these speeds based on the nature of destruction and accidents: up to 170-200 m/s, and sometimes even 350-360 m/s - more than the speed of sound.
The lifetime of a tornado varies and ranges from several minutes to several hours.
The speed at which tornadoes move is also different. Sometimes the cloud moves very slowly, almost stands still, sometimes it rushes at high speed. Meteorologists determine the average speed of tornadoes to be 40-60 km/h, but sometimes this speed reaches 200 km/h. During its movement, a tornado travels an average distance of 20-30 km. However, cases of tornadoes passing 100-120 km are not uncommon.
Marine waterspouts usually originate in groups from a single parent cloud. They most often form and reach their greatest strength near thunderstorm cumulonimbus clouds. Sometimes they accompany tropical cyclones.
Tornadoes are visible from a fairly large distance and are easily detected on the radar screen, and therefore, when they see the approach of this natural formation, navigators must take measures to avoid meeting it.
Rare but very dangerous phenomena have long been noticed at sea: - loss of buoyancy during the eruption of underwater volcanoes, of which there are many in the oceans (this creates a water-air mixture) or due to gas breakthrough from the bottom of the sea.
CONCLUSION
In conclusion, we should recall the basic rule of a sailor - there is nothing secondary at sea . At a given specific moment in time, in a given place, the effect of any natural factor can be most strongly manifested, resulting in consequences - even a catastrophe.
Therefore, the skipper must always "consider your place closer to danger" not only in the literal navigational sense of this, but also taking into account all other navigation conditions. Even simple knowledge of the very factor of the influence of these phenomena on navigation, and even more so a qualitative assessment of the effect, allows us to minimize possible negative consequences.
