Tropical and equatorial water masses. What water masses are the most mobile

Water masses are classified not only by depth, but also by origin. Regarding this, they are:

equatorial,
tropical,
moderate,
polar.

Equatorial water masses are formed in the equator region, therefore they are well warmed up by the Sun. The water temperature is +27, +28 degrees and changes only by 2 degrees during the seasons. Abundant precipitation and rivers flowing into the ocean greatly desalinate the water, so the salinity of equatorial waters is lower compared to tropical latitudes.

The water masses of tropical latitudes are also well warmed up by the Sun, but their temperature is lower and is +20, +25 degrees, and in the seasons it changes by 4 degrees. Currents have a great influence on water temperature. Warm currents from the equator are common in the western parts of the ocean, so the water will be warmer here. Cold currents enter the eastern part of the ocean and reduce the water temperature.

In tropical latitudes, descending air currents dominate, as a result of which a high atmospheric pressure is established with a small amount of precipitation. There are few rivers here and their desalination effect is insignificant, therefore, the salinity of water in this area is high.

To the north, there are temperate latitudes, where moderate water masses are formed. The seasonal distribution of temperatures is clearly manifested here, and the difference is 10 degrees. Winter temperatures range from 0 to 10 degrees, while in summer the change occurs from 10 to 20 degrees.

The salinity of temperate water masses is lower than that of tropical ones, because atmospheric precipitation, rivers flowing into the ocean, and icebergs entering these latitudes have a great desalination effect.

The western and eastern parts of the oceans within temperate latitudes also have temperature differences. The western parts of the oceans will be cold, and the eastern parts will warm the warm currents.

In the Arctic region and off the coast of Antarctica, polar water masses are formed, which, with the help of currents, are carried to temperate latitudes, sometimes they reach tropical latitudes. A feature of polar water masses is the presence of floating ice, which has a strong desalination effect. Therefore, the salinity of polar water masses is low.

Remark 1

There are no clear boundaries between water masses of different origins; there are only transition zones, which are more pronounced in those places where the contact of warm and cold currents occurs.

Water masses depending on criteria

Depending on the criteria, a different amount of water masses are allocated.

The largest in terms of volume in the World Ocean is the Antarctic bottom water mass, which occupies the bottom layer around the continent. It extends northward in the Atlantic Ocean to 40 parallel north latitude. The meridional section of this water mass shows a lower temperature and salinity compared to the waters above. The main place of its formation is the Weddell Sea and the shelf around Antarctica, where favorable conditions were formed for this. The salinity of the Antarctic bottom water mass is 34.6 ppm, and the temperature is -0.4 degrees. From the place of its formation, it slowly moves to the Atlantic, participating in the horizontal circulation of the ocean waters;

The second largest in the World Ocean is the deep and bottom North Atlantic water mass. Its formation takes place in the winter between Greenland and Iceland. Here, the warm and salty water of the North Atlantic Current is mixed with cold and more fresh water East Greenland Current. The temperature of this water mass in the formation area varies with depth from 2.8 to 3.3 degrees, and salinity also changes from 34.90 to 34.96 ppm. The North Atlantic deep and bottom water mass from the formation area spreads to the south to a depth of 2000-4000 m over the Antarctic bottom water. The rise of the ocean floor prevents it from moving northward;

Figure 1. North Atlantic water mass. Author24 - online exchange of student papers

Remark 2

To form a similar water mass in Pacific there are no conditions.

Surface water is the Antarctic intermediate water mass, which in the convergence zone spreads to the north to a depth of 1000-1500 m. In the Atlantic Ocean it is noticeable up to 15 degrees north latitude. Its salinity is minimal here and is equal to 33.8 ppm, the temperature is lowered to 2.2 degrees;

For stationary subtropical highs atmospheric pressure the formation of central water masses is characteristic. Their peculiarity is maximum salinity. On their periphery, intense convection develops during periods of cooling, as a result of which the central masses increase their thickness in the Pacific Ocean to 200-300 m, and in the Sargasso Sea of \u200b\u200bthe Atlantic Ocean their thickness increases to 900 m;

In the equatorial region, the equatorial water masses of 3 oceans - the Pacific, Indian and Atlantic - are formed. Due to the fact that a lot of precipitation falls in the equatorial region, these water masses are strongly freshened in comparison with the central water masses. Equatorial water mass is less pronounced in the Atlantic Ocean, because there is a transfer of water from the Southern to the Northern Hemisphere;

In the formation of the deep waters of the Atlantic Ocean, a rather noticeable role is played by the Mediterranean water mass, the temperature of which is 13.0-13.6 degrees, and the salinity is 38.4-38.7 ppm. This mass of water has a high density, due to which, having flown through the Strait of Gibraltar, it sinks to a depth of 1000 m and spreads like a fan over the vast expanse of the North Atlantic;

In the northwestern Indian Ocean, a similar role is played by the Red Sea water mass with a temperature of 23 degrees and a salinity of 40 ppm.

Other types of water masses

The formation of the Antarctic circumpolar water mass involves the North Atlantic deep and bottom water, rising near Antarctica, to which a certain amount of Antarctic intermediate and bottom water is mixed.

The mixture that forms rises as an independent mass of water into the upper layer of the ocean. It sits between Antarctic coastal waters and Antarctic convergence.

Antarctic circumpolar water in the circular transport of waters forms a ring that encircles Antarctica.

The upper layer of the Antarctic circumpolar water is characterized by zonal transport divergence, which causes the rise of the North Atlantic deep and bottom water in the Antarctic region.

Between Antarctic Convergence and southern border the central water masses are the subantarctic water mass. It forms a closed ring in which it moves from west to east. This water mass is the result of the mixing of central water masses with Antarctic intermediate water at their southern periphery.

In the Northern Hemisphere, in a large area of \u200b\u200bthe Pacific Ocean, north of the 40th parallel, there is a subarctic water mass. It was formed by the processes of cooling and freshening of waters in the Bering and Okhotsk seas, as well as in the adjacent part of the ocean.

In the Atlantic, this type of water is formed in small quantities.

Four water masses are present in the Arctic Ocean, and the entire water column has a negative temperature, with a positive temperature there is only a thin layer of water.

The active layer of the ocean with freshened waters and negative temperatures sinks to a depth of 200-250 m - this is the surface water mass. In winter, this layer is completely covered by convection, and the temperature drops almost to the freezing point - about -1.7 degrees.

In summer, the temperature is slightly above freezing point. The salinity on the surface of this water mass is 31.3-31.5 ppm.

A unique phenomenon in the World Ocean is the warm Atlantic layer formed from the warm West Spitsbergen Current. In order for this water mass, due to its high density, to sink under the surface layer of the Arctic Ocean with its salinity up to 34.75 ppm, it is enough for the water to cool down to 3-4 degrees.

Then it spreads over the entire ocean area at a depth of 200-500 m and even near the Bering Strait it retains high salinity and a positive temperature of +0.4 degrees.

Deep and bottom water masses are formed in the Greenland Sea.

Remark 3

Thus, the water masses that form in certain areas of the World Ocean reflect well the vertical and horizontal zoning, which is the main geographic regularity of the planet's nature.

The entire mass of the waters of the World Ocean is conventionally divided into surface and deep. Surface waters - a layer 200-300 m thick - are very heterogeneous in terms of natural properties; they can be called oceanic troposphere.The rest of the waters - oceanic stratosphere,constituting the main mass of waters, more homogeneous.

Surface waters are a zone of active thermal and dynamic interaction

ocean and atmosphere. In accordance with zonal climatic changes, they are subdivided into different water masses, primarily by their thermohaline properties. Water masses- These are relatively large volumes of water that form in certain zones (foci) of the ocean and have stable physical, chemical and biological properties for a long time.

Lyubushkin

Allocate five typeswater masses: equatorial, tropical, subtropical, subpolar and polar.

Equatorial water masses(O - 5 ° N) form inter-trade countercurrents. They have constantly high temperatures (26 - 28 ° C), a clearly pronounced layer of temperature jump at a depth of 20 - 50 m, low density and salinity - 34 - 34.5% 0, low oxygen content - 3 - 4 g / m 3, a slight saturation with life forms. The rise of water masses prevails. In the atmosphere above them there is a belt of low pressure and calm.

Tropical water masses(5 - 35 ° N sh. and 0-30 ° S. sh.) are distributed along the equatorial periphery of subtropical baric maxima; they form trade winds. The temperature in summer reaches +26 ... + 28 ° С, in winter it drops to +18 ... +20 ° С, and it differs near the western and eastern coasts due to currents and coastal stationary upwellings and downwellings. Upwelling(eng. iryueShpd- surfacing) - the ascending movement of water from a depth of 50-100 m, generated by off-set winds off the western coasts of the continents in a strip of 10-30 km. Having a low temperature and, therefore, a significant oxygen saturation, deep waters rich in biogenic and mineral substances, entering the surface illuminated zone, increase the productivity of the water mass. Downwellings- downdrafts off the eastern coasts of the continents due to the surge of water; they carry heat and oxygen down. The temperature jump layer is expressed throughout the year, salinity 35-35.5% 0, oxygen content 2-4 g / m 3.

Subtropical water massespossess the most characteristic and stable properties in the "core" - circular areas bounded by large currents. The temperature during the year varies from 28 to 15 ° C, there is a layer of temperature jump. Salinity 36-37% o, oxygen content 4 - 5 g / m 3. In the center of the gyres, the waters sink. In warm currents, subtropical water masses penetrate into temperate latitudes up to 50 ° C. sh. and 40-45 ° S. sh. These transformed subtropical water masses occupy here almost entirely the waters of the Atlantic, Pacific and Indian oceans. As they cool, subtropical waters give off a huge amount of heat to the atmosphere, especially in winter, playing a very significant role in planetary heat exchange between latitudes. The boundaries of subtropical and tropical waters are very arbitrary, therefore

some oceanographers combine them into one type of tropical waters.

Subpolar- subarctic (50 - 70 ° N) and subantarctic (45 - 60 ° S) water masses. Typical for them is a variety of characteristics both by seasons of the year and by hemispheres. The temperature in summer is 12-15 ° С, in winter 5 - 7 ° С, decreasing towards the poles. There is practically no sea ice, but there are icebergs. The temperature jump layer is expressed only in summer. Salinity decreases from 35 to 33% o towards the poles. The oxygen content is 4-6 g / m 3, so the waters are rich in life forms. These water masses occupy the North Atlantic and Pacific Ocean, penetrating in cold currents along the eastern coasts of the continents to temperate latitudes. In the southern hemisphere, they form a continuous zone south of all continents. In general, this is the western circulation of air and water masses, a strip of storms.

Polar water massesin the Arctic and around Antarctica, they have low temperatures: in summer about 0 ° C, in winter -1.5 ... -1.7 ° C. Brackish sea and fresh continental ice and their fragments are permanent here. There is no temperature jump layer. Salinity 32-33% 0. The maximum amount of oxygen is dissolved in cold waters - 5 - 7 g / m 3. On the border with subpolar waters, a sinking of dense cold waters is observed, especially in winter.

Each water mass has its own focus of formation. When water masses with different properties meet, oceanological fronts, or convergence zones (lat. concomitantly- converge). They usually form at the junction of warm and cold surface currents and are characterized by a sinking of water masses. There are several frontal zones in the World Ocean, but the main ones are four, two each in the northern and southern hemispheres. In temperate latitudes, they are expressed off the eastern coasts of the continents at the boundaries of the subpolar cyclonic and subtropical anticyclonic gyres with their respective cold and warm currents: near Newfoundland, Hokkaido, the Falkland Islands, and New Zealand. In these frontal zones, hydrothermal characteristics (temperature, salinity, density, current velocities, seasonal temperature fluctuations, sizes of wind waves, amount of fog, cloudiness, etc.) reach extreme values. To the east, due to the mixing of waters, the frontal contrasts are blurred. It is in these zones that frontal cyclones of extratropical latitudes originate. Two frontal zones exist on both sides of the thermal equator off the western shores of the motherland.

coves between tropical relatively cold waters and warm equatorial waters of inter-trade countercurrents. They are also distinguished by high values \u200b\u200bof hydrometeorological characteristics, high dynamic and biological activity, and intense interaction between the ocean and the atmosphere. These are areas of origin of tropical cyclones.

Is in the ocean and divergence zones (lat. c ^^ Ve ^ §en (o- deviate) - zones of divergence of surface currents and the rise of deep waters: at the western coasts of temperate continents and above the thermal equator at the eastern coasts of the continents. Such zones are rich in phyto- and zooplankton, are distinguished by increased biological productivity, and are areas of effective fishing.

The depth of the oceanic stratosphere is divided into three layers, differing in temperature, illumination and other properties: intermediate, deep and bottom waters. Intermediate waters are located at depths from 300-500 to 1000-1200 m. Their thickness is maximum in polar latitudes and in the central parts of anticyclonic gyres, where water subsidence prevails. Their properties are somewhat different depending on the breadth of distribution. General transfer

these waters are directed from high latitudes towards the equator.

Deep and especially bottom waters (the thickness of the latter layer is 1000-1500 m above the bottom) are distinguished by high uniformity (low temperatures, oxygen richness) and a slow speed of movement in the meridional direction from polar latitudes to the equator. Especially widespread are the Antarctic waters, "sliding" from the continental slope of Antarctica. They not only occupy the entire southern hemisphere, but also reach 10-12 ° N. sh. in the Pacific Ocean, up to 40 ° N. sh. in the Atlantic and to the Arabian Sea in the Indian Ocean.

From the characteristics of water masses, especially surface ones, and currents, the interaction of the ocean and the atmosphere is clearly visible. The ocean provides the atmosphere with the bulk of the heat, converting the sun's radiant energy into thermal energy. The ocean is a huge distiller that supplies the land with fresh water through the atmosphere. The heat entering the atmosphere from the oceans causes different atmospheric pressures. The difference in pressure creates wind. It causes excitement and currents that transfer heat to high latitudes or cold to low latitudes, etc. The processes of interaction between the two shells of the Earth - the atmosphere and the oceanosphere - are complex and diverse.

Water masses - these are large volumes of water formed in certain parts of the ocean and differing from each other in temperature, salinity, density, transparency, oxygen content and other properties. In contrast, it is of great importance in them. Depending on the depth, there are:

Surface water masses... They are formed under the influence of atmospheric processes and the influx of fresh water from the mainland to a depth of 200-250 m. Here salinity often changes, and their horizontal transport in the form of ocean currents is much stronger than the deep transport. Surface waters have the highest levels of plankton and fish;

Intermediate water masses... They have a lower boundary within the range of 500-1000 m. In intermediate water masses are formed under conditions of increased evaporation and constant rise. This explains the fact that intermediate waters occur between 20 ° and 60 ° in the Northern and Southern Hemispheres;

Deep water masses... They are formed as a result of mixing of surface and intermediate, polar and tropical water masses. Their lower boundary is 1200-5000 m. Vertically, these water masses move extremely slowly, and horizontally they move at a speed of 0.2-0.8 cm / s (28 m / h);

Bottom water masses... They occupy an area below 5000 m and have constant salinity, very high density, and their horizontal movement is slower than vertical.

Depending on the origin, the following types of water masses are distinguished:

Tropical... They form in tropical latitudes. The water temperature here is 20-25 °. The temperature of tropical water masses is greatly influenced ocean currents... The western parts of the oceans are warmer, where warm currents (see) come from the equator. The eastern parts of the oceans are colder as cold currents come here. Seasonally, the temperature of tropical water masses changes by 4 °. The salinity of these water masses is much higher than the equatorial ones, since as a result of the descending air currents, little precipitation is established and falls here;

water masses... In the temperate latitudes of the Northern Hemisphere, the western parts of the oceans, where cold currents pass, are cold. The eastern regions of the oceans are warmed by warm currents. Even in the winter months, the water in them has a temperature of 10 ° C to 0 ° C. In summer, it changes from 10 ° C to 20 ° C. Thus, the temperature of the temperate water masses differs by 10 ° C over the seasons. They are already characterized by the change of seasons. But it comes later than on land, and is not so pronounced. The salinity of temperate water masses is lower than that of tropical ones, since the desalination effect is exerted not only by rivers and atmospheric precipitation that fall here, but also entering these latitudes;

Polar water masses... Formed in and off the coast. These water masses can be carried away by currents to temperate and even tropical latitudes. In the polar regions of both hemispheres, water cools down to -2 ° C, but still remains liquid. Further lowering leads to the formation of ice. The polar water masses are characterized by an abundance of floating ice, as well as ice, which forms huge ice spaces. It stays in ice all year round and is in constant drift. In the Southern Hemisphere, in areas of polar water masses, they go into temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since ice has a strong desalination effect. There are no clear boundaries between the listed water masses, but there are transition zones - zones of mutual influence of neighboring water masses. They are most distinctly expressed in places where warm and cold currents meet. Each water mass is more or less homogeneous in its properties, but in the transition zones, these characteristics can change dramatically.

Water masses actively interact with: they give it heat and moisture, absorb carbon dioxide from it, and release oxygen.

Education

What are water masses and their types? The main types of water masses

30 September 2017

The total mass of all waters of the World Ocean is subdivided by specialists into two types - surface and deep. However, this division is very arbitrary. A more detailed categorization includes the following several groups, distinguished on the basis of territorial location.

Definition

First, let's give a definition of what water masses are. In geography, this designation refers to a sufficiently large volume of water that is formed in one or another part of the ocean. Water masses differ from each other in a number of characteristics: salinity, temperature, as well as density and transparency. Differences are also expressed in the amount of oxygen, the presence of living organisms. We have given a definition of what water masses are. Now it is necessary to consider their different types.

Water at the surface

Surface waters are those zones where their thermal and dynamic interaction with air occurs most actively. In accordance with the climatic characteristics inherent in certain zones, they are divided into separate categories: equatorial, tropical, subtropical, polar, subpolar. Students who are collecting information to answer the question of what water masses are, need to know about the depth of their occurrence. Otherwise, the answer in a geography lesson will be incomplete.

Surface waters reach a depth of 200-250 m. Their temperature often changes, since they are formed by the influence of atmospheric precipitation. Waves and horizontal ocean currents are formed in the surface water column. It is here that the largest amount of fish and plankton is found. Between the surface and deep masses there is an interlayer of intermediate water masses. The depth of their location ranges from 500 to 1000 m. They are formed in areas of high salinity and high levels of evaporation.

Deep water masses

The lower boundary of deep waters can sometimes reach 5000 m. This type of water masses most often comes across in tropical latitudes. They are formed under the influence of surface and intermediate waters. For those interested in what water masses are, and what are the features of their various types, it is also important to have an idea of \u200b\u200bthe speed of the current in the ocean. Deep water masses move very slowly in the vertical direction, but their horizontal speed can be up to 28 km per hour. The next layer is bottom water masses. They are located at depths of more than 5000 m.This type is characterized by a constant level of salinity, as well as high level density.

Equatorial water masses

"What are water masses and their types" is one of the compulsory topics of the course comprehensive school... The student needs to know that waters can be assigned to one group or another, not only depending on their depth, but also on their territorial location. The first type mentioned in accordance with this classification is the equatorial water masses. They are characterized by a high temperature (up to 28 ° C), low density, and low oxygen content. The salinity of such waters is low. There is a belt of low atmospheric pressure above the equatorial waters.

Tropical water masses

They are also quite well warmed up, and their temperature does not change during different seasons by more than 4 ° C. Ocean currents have a great influence on this type of water. Their salinity is higher, since a zone of high atmospheric pressure is established in this climatic zone, and very little precipitation falls.

Moderate water masses

The salinity level of these waters is lower than that of others, because precipitation, rivers, icebergs have a desalination effect on them. In seasons, the temperature of water masses of this type can vary up to 10 ° C. However, the change of seasons occurs much later than on the mainland. Temperate waters differ depending on whether they are in the western or eastern regions of the ocean. The former, as a rule, are cold, and the latter are warmer due to warming by internal currents.

Polar water masses

What are the coldest water masses? Obviously, they are those that are in the Arctic and off the coast of Antarctica. With the help of currents, they can be carried to temperate and tropical regions. The main features of polar water masses are floating blocks of ice and vast ice spaces. Their salinity is extremely low. In the Southern Hemisphere sea \u200b\u200bice move to the region of temperate latitudes much more often than it happens in the north.

Formation methods

Students who are interested in what water masses are will also be interested in learning information about their education. The main method of their formation is convection, or mixing. As a result of mixing, the water is immersed to a considerable depth, where vertical stability is again achieved. This process can take place in several stages, and the depth of convective mixing can reach up to 3-4 km. The next way is subduction, or "diving". With this method of mass formation, the water is lowered due to the combined action of wind and surface cooling.

These are large volumes of water that form in certain parts of the ocean and differ from each other. temperature, salinity, density, transparency, the amount of oxygen contained and many other properties. In contrast, vertical zoning is of great importance in them.

AT depending on depth the following types of water masses are distinguished:

Surface water masses . They go deep 200-250 m... The water temperature and salinity often change here, since these water masses are formed under the influence of the influx of fresh continental waters. In surface water masses are formed waves and horizontal... In this type of water masses the highest content of plankton and fish.

Intermediate water masses ... They go deep 500-1000 m... Basically, this type of masses is found in tropical latitudes of both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity.

Deep water masses ... Their lower limit may be before 5000 m... Their formation is associated with mixing of surface and intermediate water masses, polar and tropical masses. They move vertically very slowly, but horizontally - at a speed of 28 m / h.

Bottom water masses ... They are located in below 5000 m, have constant salinity and very high density.

Water masses can be classified not only depending on the depth, but also by origin... In this case, the following types of water masses are distinguished:

Equatorial water masses ... They are well warmed up by the sun, their temperature changes by no more than 2 ° C and is 27 - 28 ° C. They are desalinated by abundant atmospheric precipitation and flowing into the ocean in these latitudes, so the salinity of these waters is lower than in tropical latitudes.

Tropical water masses ... They are also well warmed up by the sun, but the water temperature here is lower than in equatorial latitudes, and is 20-25 ° С. Seasonally, the temperature of the waters in tropical latitudes changes by 4 °. The temperature of the waters of this type of water masses is greatly influenced by ocean currents: the western parts of the oceans, where warm currents come from the equator, are warmer than the eastern ones, since cold currents come there... The salinity of these waters is much higher than the equatorial ones, since here, as a result of the descending air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Moderate water masses ... According to the seasons, the temperature of the waters of these latitudes differs by 10 °: in winter the water temperature fluctuates from 0 ° to 10 ° С, and in summer it changes from 10 ° to 20 ° С. These waters are already characterized by the change of seasons, but it comes later than on land, and is not so pronounced. The salinity of these waters is lower than that of tropical waters, since atmospheric precipitation, rivers flowing into these waters, and entering these latitudes have a desalination effect. Temperate water masses are also characterized by temperature differences between the western and eastern parts of the ocean: the western parts of the oceans are cold, where cold currents pass, and the eastern regions are warmed by warm currents.

Polar water masses ... They form in the Arctic and off the coast and can be carried by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice, which forms huge ice spaces. In the Southern Hemisphere, in regions of polar water masses, sea ice penetrates into temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

Between different kinds water masses differing in origin, there are no clear boundaries, but there are transition zones... They are most pronounced in places where warm and cold currents meet.

Water masses actively interact with: they give it moisture and heat and absorb carbon dioxide from it, release oxygen.

The most characteristic properties of water masses are and.

Air masses

Transformation of air masses

The influence of the surface over which the air masses pass affects their lower layers. This influence can cause changes in the moisture content of the air due to evaporation or precipitation, as well as changes in the temperature of the air mass as a result of the release of latent heat or heat exchange with the surface.

Tab. 1. Classification of air masses and their properties depending on the focus of formation

Tropical

Polar

Arctic or antarctic

Marine

marine tropical

(MT), warm or very

wet; formed

in the Azores region

islands in the North

Atlantic

marine polar

(MP), cold and very

wet; formed

over the Atlantic to the south

from Greenland

arctic (A)

or antarctic

(AA), very cold and dry; forms over the ice-covered part of the Arctic or over the central part of Antarctica

Continental (K)

continental

tropical (CT),

hot and dry; forming over the Sahara desert

continental

polar (KP), cold and dry; formed in Siberia in

winter period

Transformations associated with the movement of air masses are called dynamic. The air velocities at different altitudes will almost certainly differ, so the air mass does not move as a whole, and the presence of a velocity shear causes turbulent mixing. If the lower layers of the air mass are heated, then instability arises and convective mixing develops. Other dynamic changes are associated with large-scale vertical air movement.

The transformations that occur with the air mass can be indicated by adding one more letter to its basic designation. If the lower layers of the air mass are warmer than the surface over which it passes, then the letter "T" is added, if they are colder, the letter "X" is added. Consequently, with cooling, the stability of the warm sea polar air mass increases, while the heating of the cold sea polar air mass causes its instability.

Air masses and their effect on the weather in the British Isles

Weather conditions in any place on Earth can be considered as a result of the action of a certain air mass and as a consequence of the changes that have occurred to it. Great Britain, located in mid-latitudes, is affected by most types of air masses. It is thus a good example for studying weather conditions caused by the transformation of air masses near the surface. Dynamic changes, caused mainly by vertical air movements, are also very important in determining weather conditions and cannot be neglected in each case.

Polar Marine Air (MPA) reaching the British Isles is generally of the CMPA type, so this air mass is unstable. When passing over the ocean, as a result of evaporation from its surface, it retains a high relative humidity, and as a result of this - especially over the warm surface of the Earth at noon with the arrival of this air mass, cumulus and cumulonimbus clouds will appear, the temperature will drop below average, and in summer there will be showers, and in winter, precipitation can often fall in the form of snow or grains. Gusty winds and convective motions in the air will disperse dust and smoke so visibility is good.

If the marine polar air (MPV) from the source of its formation passes to the south, and then goes towards the British Isles from the southwest, it may well become warm, that is, of the type TMPV; it is sometimes referred to as "polar sea return air". It brings normal temperatures and weather, an average between the weather, which is established with the arrival of air masses CMPV and MTV.

Tropical Marine Air (MTB) is usually of the TMTV type, therefore it is stable. Having reached the British Isles after crossing the ocean and cooled down, it is saturated (or becomes close to saturation) with water vapor. This air mass brings with it mild weather, the sky becomes cloudy and visibility is poor, fog is not uncommon in the west of the British Isles. Stratus clouds are formed as they rise above orographic barriers; at the same time, drizzling rains are common, turning into stronger ones, and continuous rains fall on the eastern side of the mountain ranges.

The continental tropical air mass at its source is unstable, and although its lower layers become stable when it reaches the British Isles, the upper layers remain unstable, which can cause thunderstorms in the summer. However, in winter, the lower layers of the air mass are very stable, and any clouds that form there are of the stratus type. Typically, the arrival of such an air mass causes the temperature to rise well above average, and fog forms.

With the arrival of continental polar air in winter, the British Isles have very cold weather. In the source of formation, this mass is stable, but then in the lower layers it can become unstable and, when passing over the North Sea, will be "saturated" with water vapor to a large extent. The resulting clouds are of the Cumulus type, although Stratocumulus can also form. During the winter, the eastern part of the UK can experience heavy rain and snow or snowfall.

Arctic air (AB) can be continental (CAV) or maritime (MAV), depending on the route it has made from the source of formation to the British Isles. The KAV passes over Scandinavia on its way to the British Isles. It is similar to the continental polar air, although it is colder and therefore often brings snowfalls with it during the winter and spring periods. Arctic sea air passes over Greenland and the Norwegian Sea; it is comparable to the cold polar sea air, although colder and more volatile. In winter and spring, arctic air is characterized by heavy snowfalls, prolonged frosts and exceptionally good visibility.

Water masses and t-s diagram

When determining water masses, oceanographers use a concept similar to that which is applied to air masses. Water masses are distinguished mainly by temperature and salinity. It is also believed that water masses form in a specific area where they are in the surface mixed layer and where they are affected by constant atmospheric conditions. If the water remains in a stationary state for a long period of time, its salinity will be determined by a number of factors: evaporation and precipitation, the influx of fresh water with river runoff in coastal areas, melting and ice formation in high latitudes, etc. In the same way, its temperature will be determined by the radiation balance of the water surface, as well as the exchange of heat with the atmosphere. If the salinity of the water decreases and the temperature rises, the density of the water will decrease and the water column will become stable. Under these conditions, only a surface water mass of small thickness can form. If, however, the salinity increases and the temperature decreases, the water will become denser, sink, and a water mass may form, reaching a significant vertical thickness.

To distinguish between water masses, data on temperature and salinity obtained at different depths in a certain area of \u200b\u200bthe ocean are plotted on a diagram with temperature on the ordinate and salinity on the abscissa. All points are connected to each other by a line in ascending order of depth. If the water mass is perfectly homogeneous, it will be represented by a single point on such a diagram. It is this feature that serves as a criterion for identifying the type of water. The accumulation of observation points near such a point will show the presence of waters of a certain type. But the temperature and salinity of the water mass usually change with depth, and the water mass is characterized by T-S chart a certain curve. These variations can be caused by small fluctuations in the properties of water formed at different times of the year and sinking to different depths in accordance with its density. They can also be explained by changes in conditions on the ocean surface in the area where the formation of the water mass took place, and the water may not descend vertically, but along some inclined surfaces of equal densities. Since q1 is only a function of temperature and salinity, lines of equal values \u200b\u200bof q1 can be drawn on the T-S diagram. An idea of \u200b\u200bthe stability of the water column can be obtained by comparing t-S chart with striking isolines q1.

Conservative and non-conservative properties

Having formed, the water mass, like the air mass, begins to move from the source of formation, undergoing transformation along the way. If it remains in the surface mixed layer or leaves it, and then returns again, further interaction with the atmosphere will cause changes in temperature and salinity. A new water mass can arise as a result of mixing with another water mass, and its properties will be intermediate between the properties of the two original water masses. From the moment the water mass ceases to undergo transformation under the influence of the atmosphere, its temperature and salinity can only change as a result of the mixing process. Therefore, these properties are called conservative.

The body of water usually has certain chemical characteristics, an inherent biota, and typical temperature-salinity ratios (T-S ratios). A useful indicator characterizing the water mass is often the concentration of dissolved oxygen, as well as the concentration of biogenic substances - silicates and phosphates. Marine organisms inherent in a particular water mass are called indicator species. They can remain within a given water mass, since its physical and chemical properties satisfy them or simply because they, being plankton, are transported together with the water mass from the area of \u200b\u200bits formation. These properties, however, change as a result of chemical and biological processes in the ocean and are therefore called non-conservative properties.

Examples of water masses

A fairly clear example is the water masses that are formed in semi-enclosed reservoirs. The water mass that forms in the Baltic Sea has low salinity, which is caused by a significant excess of river flow and the amount of precipitation over evaporation. In summer, this water mass heats up sufficiently and therefore has a very low density. From its source of formation, it flows through narrow straits between Sweden and Denmark, where it intensively mixes with the underlying water layers entering the straits from the ocean. Before mixing, its temperature in summer is close to 16 ° C, and the salinity is less than 8% 0. But by the time it reaches the Skagerrak Strait, its salinity as a result of mixing increases to a value of about 20% o. Due to its low density, it remains on the surface and is rapidly transformed as a result of interaction with the atmosphere. Therefore, this mass of water has no noticeable effect on areas of the open ocean.

In the Mediterranean Sea, evaporation exceeds the influx of fresh water in the form of precipitation and river runoff, and therefore salinity increases there. In the northwest part Mediterranean Sea winter cooling (associated mainly with winds called mistral) can lead to convection that engulfs the entire water column to depths of more than 2000 m, resulting in an extremely homogeneous water mass with a salinity of more than 38.4% and a temperature of about 12.8 ° FROM. When this water mass leaves the Mediterranean Sea through the Strait of Gibraltar, it undergoes intensive mixing, and the least mixed layer, or core, of Mediterranean water in the adjacent Atlantic has a salinity of 36.5% 0 and a temperature of 11 ° C. This layer is very dense and therefore sinks to depths of about 1000 m. At this level, it spreads, undergoing continuous mixing, but its core can still be recognized among other water masses of most of the Atlantic Ocean.

In the open ocean, Central water masses are formed at latitudes from about 25 ° to 40 °, and then sink along inclined isopycnals and occupy the upper part of the main thermocline. In the North Atlantic, this water mass is characterized by T-S curve with an initial value of 19 ° C and 36.7% and a final value of 8 ° C and 35.1%. At higher latitudes, intermediate water masses are formed, which are characterized by low salinity as well as low temperatures. The most widespread is the Antarctic intermediate water mass. It has a temperature of 2 ° to 7 ° C and a salinity of 34.1 to 34.6% 0 and after submersion at about 50 ° S. sh. to a depth of 800-1000 m it spreads in a northern direction. The deepest water masses form at high latitudes, where water cools down to very low temperatures in winter, often to the freezing point, so salinity is determined by the freezing process. The Antarctic bottom water mass has a temperature of -0.4 ° C and a salinity of 34.66% 0 and spreads northward at depths of more than 3000 m.The North Atlantic deep bottom water mass, which is formed in the Norwegian and Greenland Seas and when -The Greenland Sill is undergoing a marked transformation, extends southward and overlaps the Antarctic bottom water mass in the equatorial and southern Atlantic Ocean.

The concept of water masses has played an important role in describing circulation processes in the oceans. The currents in the depths of the oceans are both very slow and very changeable, so that they can be studied through direct observation. But T-S analysis helps to isolate the cores of water masses and determine the directions of their distribution. However, to establish the speed at which they move, other data are needed, such as the stirring speed and the rate of change of non-conservative properties. But they usually cannot be obtained.

Laminar and turbulent flows

Movements in the atmosphere and in the ocean can be classified different ways... One of them is the separation of motion into laminar and turbulent. In a laminar flow, fluid particles move in an orderly manner, streamlines are parallel. The turbulent flow is chaotic and the trajectories of individual particles intersect. In a fluid that is uniform in density, the transition from laminar to turbulent regime occurs when the velocity reaches a certain critical value proportional to the viscosity and inversely proportional to the density and distance to the flow boundary. Most of the currents in the ocean and atmosphere are turbulent. In this case, the effective viscosity, or turbulent friction, in such flows is usually several orders of magnitude higher than the molecular viscosity and depends on the nature of turbulence and its intensity. In nature, there are two cases of the laminar regime. One is a flow in a very thin layer adjacent to a smooth boundary, the other is motion in layers of significant vertical stability (such as, for example, an inversion layer in the atmosphere and a thermocline in the ocean), where the vertical velocity fluctuations are small. The vertical shear of the velocity in such cases is much greater than in turbulent flows.

The scale of the movement

Another way of classifying motions in the atmosphere and ocean is based on their separation according to spatial and temporal scales, as well as on the separation of periodic and non-periodic components of the motion.

The largest spatio-temporal scales correspond to such stationary systems as trade winds in the atmosphere or the Gulf Stream in the ocean. Although the motion in them experiences fluctuations, these systems can be regarded as more or less constant elements of circulation, having a spatial scale of the order of several thousand kilometers.

The next place is occupied by processes with seasonal cyclicity. Among them, the monsoons and the currents of the Indian Ocean caused by them - and also changing their direction - should be especially noted. The spatial scale of these processes is also of the order of several thousand kilometers, but they are distinguished by a pronounced periodicity.

Processes with a time scale of several days or weeks are usually irregular and have spatial scales of up to thousands of kilometers. These include variations in wind associated with the transfer of different air masses and causing changes in weather in areas such as the British Isles, as well as similar and often associated with the first fluctuations in ocean currents.

Considering movements with a time scale from several hours to one or two days, we encounter a wide variety of processes, some of which are clearly periodic. This may be a daily frequency associated with the daily variation of solar radiation (it is typical, for example, for a breeze - a wind blowing from sea to land during the day, and from land to sea at night); it can be daily and semidiurnal frequency, characteristic of tides; this may be the frequency associated with the movement of cyclones and other atmospheric disturbances. The spatial scale of this type of motion is from 50 km (for breezes) to 2000 km (for baric depressions at mid-latitudes).

Time scales, measured in seconds, less often minutes, correspond to regular movements - waves. The most common are wind waves on the ocean surface, with a spatial scale of about 100 m. Longer waves, such as leeward waves, are also encountered in the ocean and in the atmosphere. Irregular movements with such time scales correspond to turbulent fluctuations, manifested, for example, in the form of wind gusts.

The motion observed in some region of the ocean or atmosphere can be characterized by a vector sum of velocities, each of which corresponds to a certain scale of motion. For example, the velocity measured at some point in time can be represented as where and denotes turbulent fluctuations of the velocity.

To characterize the movement, you can use the description of the forces involved in its creation. This approach, combined with the scaling method, will be used in subsequent chapters to describe various forms of motion. It is also convenient here to consider the various forces, the action of which can cause horizontal movements in the ocean and atmosphere or affect them.

Forces can be divided into three categories: external, internal, and secondary. Sources of external forces lie outside the liquid medium. The gravitational pull of the Sun and Moon, which causes tidal movements, and the force of friction of the wind, fall into this category. Internal forces are related to the distribution of mass or density in a liquid medium. Uneven density distribution is caused by uneven heating of the ocean and atmosphere, and generates horizontal pressure gradients inside the liquid medium. By secondary, we mean forces acting on a liquid only when it is in a state of motion relative to the earth's surface. The most obvious is the frictional force, always against the motion. If different layers of fluid are moving at different speeds, friction between the layers due to viscosity will slow down the faster moving layers and accelerate the less fast moving layers. If the flow is directed along the surface, then in the layer adjacent to the boundary, the friction force is directly opposite to the direction of the flow. Despite the fact that friction usually plays a minor role in atmospheric and oceanic movements, it would lead to attenuation of these movements if they were not supported by external forces. Thus, the movement could not remain uniform if other forces were absent. The other two secondary forces are bogus forces. They are associated with the choice of the coordinate system relative to which the motion is considered. This is the Coriolis force (which we have already talked about) and centrifugal forcethat appears when the body moves in a circle.

Centrifugal force

A body moving at a constant speed around a circle constantly changes its direction of motion and, therefore, experiences acceleration. This acceleration is directed towards the instantaneous center of curvature of the trajectory and is called centripetal acceleration. Therefore, in order to remain on the circle, the body must experience the action of some force directed towards the center of the circle. As shown in elementary textbooks on dynamics, the magnitude of this force is mu 2 / r, or mw 2 r, where r is the mass of the body, m is the speed of the body in a circle, r is the radius of the circle, and w is the angular velocity of rotation of the body (usually measured in radians per second). For example, for a passenger traveling in a train along a curved path, the movement appears to be uniform. He sees that he is moving relative to the surface with constant speed... However, the passenger feels the action of some force directed from the center of the circle - centrifugal force, and he counteracts this force by leaning towards the center of the circle. Then the centripetal force turns out to be equal to the horizontal component of the reaction of the support-seat or the floor of the train. In other words, to maintain its apparent state of uniform motion, the passenger needs the centripetal force to be equal in magnitude and opposite in direction to the centrifugal force.

WATER MASS, the volume of water, commensurate with the area and depth of a reservoir, with a relative homogeneity of physical, chemical and biological characteristics that are formed in specific physical and geographical conditions (usually on the surface of the ocean, sea), which differ from the surrounding water column. Features of water masses, acquired in certain areas of the oceans and seas, remain outside the area of \u200b\u200bformation. Adjacent water masses are separated from each other by zones of the World Ocean fronts, zones of separation and transformation zones, which are traced by increasing horizontal and vertical gradients of the main indicators of water masses. The main factors in the formation of water masses are the heat and water balances of a given area, respectively, the main indicators of water masses are temperature, salinity and the density depending on them. The most important geographic patterns - horizontal and vertical zoning - appear in the ocean as a specific structure of waters, consisting of a set of water masses.

In the vertical structure of the World Ocean, water masses are distinguished: surface - up to a depth of 150-200 m; subsurface - up to 400-500 m; intermediate - up to 1000-1500 m, deep - up to 2500-3500 m; bottom - below 3500 m. In each of the oceans there are characteristic water masses, surface water masses are named in accordance with the climatic zone where they formed (for example, Pacific subarctic, Pacific tropical and so on). For the underlying structural zones of the oceans and seas, the name of the water masses corresponds to their geographic area (Mediterranean intermediate water mass, North Atlantic deep, deep Black Sea, Antarctic bottom, etc.). The density of water and the peculiarities of atmospheric circulation determine the depth to which the water mass sinks in the region of its formation. Often, when analyzing the water mass, indicators of the content of dissolved oxygen, other elements, the concentration of a number of isotopes are also taken into account, which make it possible to trace the distribution of the water mass from the region of its formation, the degree of mixing with the surrounding waters, and the time spent out of contact with the atmosphere.

The characteristics of water masses do not remain constant, they are subject to seasonal (in the upper layer) and long-term fluctuations within certain limits, and change in space. As they move from the formation area, the water masses are transformed under the influence of the changed heat and water balances, the peculiarities of the circulation of the atmosphere and the ocean, and are mixed with the surrounding waters. As a result, primary water masses are distinguished (formed under the direct influence of the atmosphere, with the greatest fluctuations in characteristics) and secondary water masses (formed by mixing the primary ones, they are characterized by the greatest homogeneity of characteristics). Within the water mass, a core is distinguished - a layer with the least transformed characteristics, which retains the distinctive features inherent in a particular water mass - minima or maxima of salinity and temperature, the content of a number of chemicals.

When studying water masses, the method of temperature-salinity curves (T, S-curves), the kernel method (study of the transformation of the extrema of temperature or salinity inherent in the water mass), isopycnic method (analysis of characteristics on surfaces of equal density), statistical T, S-analysis are used. The circulation of water masses plays an important role in the energy and water balance of the Earth's climatic system, redistributing thermal energy and freshened (or saline) waters between latitudes and different oceans.

Lit .: Sverdrup H. U., Johnson M. W., Fleming R. H. The oceans. N. Y. 1942; Zubov N.N. Dynamic Oceanology. M .; L., 1947; Dobrovolskiy A.D. On the determination of water masses // Oceanology. 1961. T. 1. Iss. 1; Stepanov V.N. Oceanosphere. M., 1983; Mamaev OI Thermohaline analysis of the waters of the World Ocean. L., 1987; he is. Physical oceanography: Fav. works. M., 2000; Mikhailov V. N., Dobrovolsky A. D., Dobrolyubov S. A. Hydrology. M., 2005.

Water masses are large volumes of water that form in certain parts of the ocean and differ from each other in temperature, salinity, density, transparency, the amount of oxygen contained and many other properties. Unlike air masses, vertical zoning is of great importance in them. Depending on the depth, the following types of water masses are distinguished:

Surface water masses. They are located to a depth of 200-250 m. The water temperature and salinity often change here, since these water masses are formed under the influence of atmospheric precipitation and the influx of fresh continental waters. Waves and horizontal ocean currents are formed in surface water masses. In this type of water masses the highest content of plankton and fish.

Intermediate water masses. They are located down to a depth of 500-1000 m. Basically, this type of mass is found in the tropical latitudes of both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity. Deep water masses. Their lower boundary can reach up to 5000 m. Their formation is associated with the mixing of surface and intermediate water masses, polar and tropical masses. They move vertically very slowly, but horizontally - at a speed of 28 m / h.

Bottom water masses. They are located in the World Ocean below 5000 m, have constant salinity and very high density.

Water masses can be classified not only by depth but also by origin. In this case, the following types of water masses are distinguished:

Equatorial water masses. They are well warmed up by the sun, their temperature changes by no more than 2 ° C and is 27 - 28 ° C. They are desalinated by abundant atmospheric precipitation and rivers flowing into the ocean in these latitudes, so the salinity of these waters is lower than in tropical latitudes.

Tropical water masses. They are also well warmed up by the sun, but the water temperature here is lower than in equatorial latitudes, and is 20-25 ° С. Seasonally, the temperature of the waters in tropical latitudes changes by 4 °. Oceanic currents greatly influence the temperature of waters of this type of water masses: the western parts of the oceans, where warm currents come from the equator, are warmer than the eastern ones, since cold currents come there. The salinity of these waters is much higher than the equatorial ones, since here, as a result of the descending air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Moderate water masses. According to the seasons, the temperature of the waters of these latitudes differs by 10 °: in winter the water temperature fluctuates from 0 ° to 10 ° С, and in summer it changes from 10 ° to 20 ° С. These waters are already characterized by the change of seasons, but it comes later than on land, and is not so pronounced. The salinity of these waters is lower than that of tropical waters, since atmospheric precipitation, rivers flowing into these waters, and icebergs entering these latitudes have a desalination effect. Temperate water masses are also characterized by temperature differences between the western and eastern parts of the ocean: the western parts of the oceans are cold, where cold currents pass, and the eastern regions are warmed by warm currents.

Polar water masses. They form in the Arctic and off the coast of Antarctica and can be carried out by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice, which forms huge ice spaces. In the Southern Hemisphere, in regions of polar water masses, sea ice penetrates into temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

There are no clear boundaries between different types of water masses, differing in origin, but there are transition zones. They are most pronounced in places where warm and cold currents meet. Water masses actively interact with the atmosphere: they give it moisture and heat, absorb carbon dioxide from it, and release oxygen. The most characteristic properties of water masses are salinity and temperature.

- These are large volumes of water that form in certain parts of the ocean and differ from each other temperature, salinity, density, transparency, the amount of oxygen contained and many other properties. In contrast, it is of great importance in them.

AT depending on depth the following types of water masses are distinguished:

Intermediate water masses ... They go deep 500-1000 m... Basically, this type of mass is found in both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity.

Bottom water masses ... They are located in below 5000 m, have constant salinity and very high density.

Water masses can be classified not only depending on the depth, but also by origin... In this case, the following types of water masses are distinguished:

Equatorial water masses ... They are well warmed up by the sun, their temperature changes by no more than 2 ° C and is 27 - 28 ° C. They are desalinated by abundant atmospheric precipitation and flowing into the ocean at these latitudes, therefore the salinity of these waters is lower than in tropical latitudes.

Tropical water masses ... They are also well warmed up by the sun, but the water temperature here is lower than in, and is 20-25 ° C. Seasonally, the temperature of the waters in tropical latitudes changes by 4 °. The temperature of the waters of this type of water masses is greatly influenced by ocean currents: the western parts of the oceans, where warm currents come from the equator, are warmer than the eastern ones, since cold currents come there... The salinity of these waters is much higher than the equatorial ones, since here, as a result of the descending air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Polar water masses ... They form in the Arctic and off the coast and can be carried by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice, which forms huge ice spaces. In the Southern Hemisphere, in areas of polar water masses, they go into temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

There are no clear boundaries between different types of water masses differing in origin, but there are transition zones... They are most pronounced in places where warm and cold currents meet.

Water masses actively interact with: they give it moisture and heat and absorb carbon dioxide from it, release oxygen.

The most characteristic properties of water masses are and.

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