), are separated from each other by rather narrow transition zones, which are strongly inclined to earth's surface(less than 1°). a front is a section between having different physical properties. The intersection of the front with the earth's surface is called the front line. At the front, all the properties of the air masses—temperature, wind direction and speed, humidity, precipitation—change dramatically. The passage of the front through the place of observation is accompanied by more or less abrupt changes.

Distinguish fronts associated with cyclones, and climatic fronts.

In cyclones, fronts are formed when warm and cold air meet, while the top of the frontal system, as a rule, is in the center. Cold air meeting warm air always ends up at the bottom. It leaks under the warm, trying to push it up. Warm air, on the contrary, flows onto cold air and if it pushes it, then it itself rises along the interface plane. Depending on which air is more active, in which direction the front is moving, it is called warm or cold.

A warm front moves in the direction of cold air and means the onset of warm air. It slowly pushes cold air out. Being lighter, it flows onto the wedge of cold air, gently rising up along the interface. In this case, an extensive zone of clouds forms in front of the front, from which heavy precipitation falls. The precipitation band in front of the warm front reaches 300, and in cold weather even 400 km. Behind the front line, precipitation stops. The gradual replacement of cold air with warm air leads to a decrease in pressure and an increase in wind. After the passage of the front, there is abrupt change weather: rises, changes direction by about 90 ° and weakens, visibility deteriorates, forms, drizzling precipitation may occur.

The cold front moves towards the warm air. In this case, cold air, being denser and heavier, moves along the earth's surface in the form of a wedge, moves faster than warm air and, as it were, lifts warm air in front of it, vigorously pushing it up. Above the front line and in front of it, large cumulonimbus are formed, from which heavy rains fall, arise, and are observed strong winds. After the passage of the front, precipitation and cloudiness significantly decrease, the wind changes direction by about 90 ° and weakens somewhat, the temperature drops, air humidity decreases, its transparency and visibility increase; is growing.

The Arctic (Antarctic) front separates the Arctic (Antarctic) air from the air temperate latitudes, two temperate (polar) fronts separate temperate air and tropical air. A tropical front forms where tropical and air meet, differing in , not in temperature. All fronts, together with the boundaries of the belts, shift towards the poles in summer, and in winter. Often they form separate branches that spread over long distances from. The tropical front is always in the hemisphere where it is summer.

Watching the weather changes is very exciting. The sun gives way to rain, the rain to snow, and gusty winds blow over all this variety. In childhood, this causes admiration and surprise, in older people - a desire to understand the mechanism of the process. Let's try to understand what shapes the weather and how atmospheric fronts are related to it.

air mass boundary

In the usual perception, "front" is a military term. This is the edge on which the clash of enemy forces takes place. And the concept of atmospheric fronts is the boundaries of contact between two air masses that form over huge areas of the Earth's surface.

By the will of nature, man got the opportunity to live, evolve and populate ever larger territories. Troposphere - Bottom part Earth's atmosphere - provides us with oxygen and is in constant motion. All of it consists of separate air masses, united by a common occurrence and similar indicators. Among the main indicators of these masses determine the volume, temperature, pressure and humidity. During the movement, different masses can approach and collide. However, they never lose their boundaries and do not mix with each other. - these are areas where sharp weather jumps come into contact and occur.

A bit of history

The concepts of "atmospheric front" and "frontal surface" did not arise by themselves. They were introduced into meteorology by the Norwegian scientist J. Bjerknes. It happened in 1918. Bjerknes proved that atmospheric fronts are the main links in the high and middle layers. However, before the research of the Norwegian, back in 1863, Admiral Fitzroy suggested that violent atmospheric processes begin at the meeting places of air masses coming from different parts of the world. But at that moment science community ignored these observations.

The Bergen school, of which Bjerknes was a representative, not only carried out its own observations, but also brought together all the knowledge and assumptions expressed by earlier observers and scientists, and presented them in the form of a consistent scientific system.

A-priory, inclined surface, which is the area of ​​transition between different air flows, is called the frontal surface. But atmospheric fronts are a display of frontal surfaces on a meteorological map. Usually, the transition region of the atmospheric front is tied up near the surface of the Earth and rises up to those heights at which the differences between air masses are blurred. Most often, the threshold of this height is from 9 to 12 km.

warm front

atmospheric fronts are different. They depend on the direction of movement of warm and cold massifs. There are three types of fronts: cold, warm and occlusion, formed at the junction of different fronts. Let us consider in more detail what warm and cold atmospheric fronts are.

A warm front is a movement of air masses in which cold air gives way to warm air. That is, the air is more high temperature, advancing, is located in the territory dominated by cold air masses. In addition, it rises up along the transition zone. At the same time, the air temperature gradually decreases, due to which condensation of the water vapor in it occurs. This is how clouds form.

The main signs by which you can identify a warm atmospheric front:

  • atmospheric pressure drops sharply;
  • increases;
  • the air temperature rises;
  • cirrus appear, then cirrostratus, and after - high-stratus clouds;
  • the wind turns slightly to the left and becomes stronger;
  • clouds become nimbostratus;
  • precipitation of varying intensity falls.

It usually warms up after the precipitation stops, but this does not last long, because the cold front moves very quickly and catches up with the warm atmospheric front.

cold front

Such a feature is observed: a warm front is always inclined in the direction of movement, and a cold front is always inclined in the opposite direction. When fronts move, cold air wedges into warm air, pushing it up. Cold atmospheric fronts lead to a decrease in temperature and cooling over a large area. As the rising warm air masses cool, the moisture condenses into clouds.

The main signs by which a cold front can be identified are:

  • before the front, the pressure drops, behind the line of the atmospheric front it rises sharply;
  • cumulus clouds form;
  • a gusty wind appears, with a sharp change in direction clockwise;
  • starts pouring rain with a thunderstorm or hail, the duration of precipitation is about two hours;
  • the temperature drops sharply, sometimes by 10 ° C at once;
  • Numerous clearings are observed behind the atmospheric front.

Traveling through a cold front is no easy task for travelers. Sometimes you have to overcome whirlwinds and squalls in conditions of poor visibility.

Front of occlusions

It has already been said that atmospheric fronts are different, if everything is more or less clear with warm and cold fronts, then the front of occlusions raises a lot of questions. The formation of such effects occurs at the junction of cold and warm fronts. The warmer air is forced upward. The main action occurs in cyclones at the moment when a more rapid cold front catches up with a warm one. As a result, there is a movement of atmospheric fronts and a collision of three air masses, two cold and one warm.

The main features by which you can determine the front of occlusions:

  • clouds and precipitation of a general type;
  • abrupt shifts without a strong change in speed;
  • smooth pressure change;
  • no sudden temperature changes;
  • cyclones.

The occlusion front depends on the temperature of the cold air masses in front of it and behind it. Distinguish between cold and warm occlusion fronts. The most difficult conditions are observed at the moment of direct closure of the fronts. As the warm air is displaced, the front is eroded and improved.

Cyclone and anticyclone

Since the concept of "cyclone" was used in the description of the front of occlusions, it is necessary to tell what kind of phenomenon it is.

Due to the uneven distribution of air in the surface layers, zones of high and low pressure. Zones high pressure characterized by an excess amount of air, low - its insufficient amount. As a result of the air flow between the zones (from excess to insufficient), wind is formed. A cyclone is an area of ​​low pressure that draws in, like a funnel, the missing air and clouds from areas where they are in excess.

An anticyclone is an area of ​​high pressure that pushes excess air into areas of low pressure. The main characteristic is clear weather, since clouds are also forced out of this zone.

Geographic division of atmospheric fronts

Depending on the climatic zones, over which atmospheric fronts are formed, they are divided geographically into:

  1. Arctic, separating cold Arctic air masses from temperate ones.
  2. Polar, located between the temperate and tropical masses.
  3. Tropical (trade wind), delimiting the tropical and equatorial zones.

Influence of the underlying surface

On physical properties air masses are affected by radiation and the appearance of the Earth. Since the nature of such a surface can be different, the friction against it occurs unevenly. Difficult geographic topography can deform the atmospheric front line and change its effects. For example, there are known cases of destruction of atmospheric fronts when crossing mountain ranges.

Air masses and atmospheric fronts bring many surprises to forecasters. Comparing and studying the directions of mass movement and the vagaries of cyclones (anticyclones), they make graphs and forecasts that people use every day, without even thinking about how much work is behind it.

The weather in our country is unstable. This is especially evident in the European part of Russia. This is due to the fact that different air masses meet: warm and cold. Air masses differ in properties: temperature, humidity, dust content, pressure. Atmospheric circulation allows air masses to move from one part to another. Where air masses of different properties come into contact, atmospheric fronts.

Atmospheric fronts are inclined to the Earth's surface, their width reaches from 500 to 900 km, and they extend for 2000-3000 km in length. In the frontal zones, there is an interface between two types of air: cold and warm. Such a surface is called frontal. As a rule, this surface is inclined towards cold air - it is located under it as a heavier one. And warm air, lighter, is located above the frontal surface (see fig. 1).

Rice. 1. Atmospheric fronts

The line of intersection of the frontal surface with the surface of the Earth forms front line, which is also briefly called front.

atmospheric front- transitional zone between two dissimilar air masses.

Warm air, being lighter, rises. Rising, it cools, saturated with water vapor. Clouds form and precipitation falls. Therefore, the passage of an atmospheric front is always accompanied by precipitation.

Depending on the direction of movement, moving atmospheric fronts are divided into warm and cold. warm front formed when warm air flows into cold air. The front line moves in the direction of cold air. After the passage of a warm front, warming occurs. The warm front forms a continuous band of clouds hundreds of kilometers long. There are long drizzling rains, and warming comes. The rise of air during the onset of a warm front occurs more slowly compared to a cold front. Cirrus and cirrostratus clouds forming high in the sky are a harbinger of an approaching warm front. (see Fig. 2).

Rice. 2. Warm atmospheric front ()

It is formed when cold air leaks under warm air, while the front line moves towards warm air, which is forced upward. As a rule, a cold front moves very quickly. This causes strong winds, heavy, often heavy rainfall with thunderstorms, and blizzards in winter. After the passage of a cold front, a cold snap sets in. (See Fig. 3).

Rice. 3. Cold front ()

Atmospheric fronts are stationary and moving. If air currents do not move towards cold or towards warm air along the front line, such fronts are called stationary. If the air currents have a movement velocity perpendicular to the front line and move either towards cold or towards warm air, such atmospheric fronts are called moving. Atmospheric fronts arise, move and collapse in about a few days. The role of frontal activity in climate formation is more pronounced in temperate latitudes; therefore, unstable weather is typical for most of Russia. The most powerful fronts occur when the main types of air masses come into contact: arctic, temperate, tropical (see Fig. 4).

Rice. 4. Formation of atmospheric fronts in Russia

Zones reflecting their long-term positions are called climate fronts. On the border between arctic and temperate air, over the northern regions of Russia, a arctic front. Air masses of temperate latitudes and tropical ones are separated by a polar temperate front, which is located mainly to the south of the borders of Russia. The main climatic fronts do not form continuous strips of lines, but are broken into segments. Long-term observations have shown that the Arctic and Polar fronts are shifting southward in winter and northward in summer. In the east of the country, the Arctic front reaches the coast of the Sea of ​​Okhotsk in winter. To the northeast of it, very cold and dry arctic air dominates. In European Russia, the Arctic front does not move that far. This is where the warming effect of the North Atlantic Current comes into play. The branches of the polar climate front stretch over the southern territories of our country only in summer, in winter they lie over mediterranean sea and Iran and occasionally capture the Black Sea.

In the interaction of air masses take part cyclones And anticyclones- large moving atmospheric vortices carrying atmospheric masses.

Low area atmospheric pressure with a certain system of winds blowing from the edges to the center and deviating counterclockwise.

An area of ​​high atmospheric pressure with a specific pattern of winds blowing from the center to the edges and deviating clockwise.

Cyclones are impressive in size, extend into the troposphere to a height of up to 10 km, and a width of up to 3000 km. Pressure increases in cyclones and decreases in anticyclones. In the northern hemisphere, the winds blowing towards the center of the cyclones are deflected by the force of the axial rotation of the earth to the right (the air spins counterclockwise), and in the central part the air rises. In anticyclones, the winds directed to the outskirts also deviate to the right (the air swirls clockwise), and in the central part the air descends from the upper layers of the atmosphere down (see fig. 5, fig. 6).

Rice. 5. Cyclone

Rice. 6. Anticyclone

The fronts on which cyclones and anticyclones originate are almost never rectilinear, they are characterized by wavy bends. (See Fig. 7).

Rice. 7. Atmospheric fronts (synoptic map)

In the formed bays of warm and cold air, rotating tops are formed atmospheric vortices (see fig. 8).

Rice. 8. Formation of an atmospheric vortex

Gradually, they separate from the front and begin to move and carry air on their own at a speed of 30-40 km / h.

Atmospheric vortices live for 5-10 days before destruction. And the intensity of their formation depends on the properties of the underlying surface (temperature, humidity). Several cyclones and anticyclones form daily in the troposphere. There are hundreds of them throughout the year. Every day our country is under the influence of some kind of atmospheric vortex. Since the air rises in cyclones, cloudy weather with precipitation and winds is always associated with their arrival, cool in summer and warm in winter. During the entire stay of the anticyclone, cloudless dry weather prevails, hot in summer And frosty in winter. This is facilitated by the slow sinking of air down from the higher layers of the troposphere. The descending air heats up and becomes less saturated with moisture. In anticyclones, the winds are weak, and in their inner parts there is complete calm - calm(see fig. 9).

Rice. 9. Air movement in an anticyclone

In Russia, cyclones and anticyclones are confined to the main climatic fronts: polar and arctic. They also form on the border between maritime and continental air masses of temperate latitudes. In the west of Russia, cyclones and anticyclones arise and move in the direction of the general air transport from west to east. In the Far East, in accordance with the direction of the monsoons. When moving with westward transfer in the east, cyclones deviate to the north, and anticyclones deviate to the south (see fig. 10). Therefore, the paths of cyclones in Russia most often pass through the northern regions of Russia, and anticyclones - through the southern ones. In this regard, the atmospheric pressure in the north of Russia is lower, there may be inclement weather for many days in a row, in the south there are more sunny days, dry summer and snowy winter.

Rice. 10. Deviation of cyclones and anticyclones when moving from the west

Areas where intense winter cyclones pass: the Barents, Kara, Okhotsk Seas and the northwest of the Russian Plain. In summer, cyclones are most frequent on Far East and in the west of the Russian Plain. Anticyclonic weather prevails throughout the year in the south of the Russian Plain, in the south of Western Siberia, and in winter over all of Eastern Siberia, where the Asian maximum pressure is established.

The movement and interaction of air masses, atmospheric fronts, cyclones and anticyclones change the weather and affect it. Data on weather changes are plotted on special synoptic maps for further analysis weather conditions on the territory of our country.

The movement of atmospheric vortices leads to a change in the weather. Her condition for each day is recorded on special maps - synoptic(see fig. 11).

Rice. 11. Synoptic map

Weather observations are carried out by an extensive network of meteorological stations. Then the results of the observations are transmitted to the centers of hydrometeorological data. Here they are processed, and weather information is applied to synoptic maps. The maps show atmospheric pressure, fronts, air temperature, wind direction and speed, cloudiness and precipitation. The distribution of atmospheric pressure indicates the position of cyclones and anticyclones. Having studied the patterns of flow atmospheric processes you can predict the weather. Accurate forecast weather is an extremely complex matter, since it is difficult to take into account the whole complex of interacting factors in their constant development. Therefore, even short-term forecasts of the hydrometeorological center are not always justified.

Source).).

  • Dust storm over the Arabian Sea ().
  • Cyclones and anticyclones ().

    • Homework

    1. Why does precipitation fall in the atmospheric front zone?
    2. What is the main difference between a cyclone and an anticyclone?

    Atmospheric fronts have several various characteristics. On them there is a division of this natural phenomenon on different types.

    Atmospheric fronts can reach a width of 500-700 km, and extend for 3000-5000 km in length.
    Atmospheric fronts are classified by movement relative to the location of air masses. Another criterion is the spatial extent and circulation significance. And finally, a geographical feature.

    Characteristics of atmospheric fronts

    By movement, atmospheric fronts can be divided into cold, warm and occlusive fronts.
    Warm atmospheric air masses are formed when warm air masses, as a rule, wet ones move on to drier and colder ones. The approaching warm front brings a gradual decrease in atmospheric pressure, a slight increase in air temperature and small but prolonged precipitation.

    A cold front is formed under the influence of northerly winds that force cold air into areas previously occupied by a warm front. A cold atmospheric front affects the weather in a small band and is often accompanied by thunderstorms and a decrease in atmospheric pressure. After the front passes, the air temperature drops sharply, and the pressure increases.

    The cyclone, which is considered the most powerful and destructive in history, hit the Ganges Delta in eastern Pakistan in November 1970. The wind speed reached more than 230 km / h, and the height of the tidal wave was about 15 meters.

    Occlusion fronts occur when one atmospheric front superimposes on another, formed earlier. Between them is a significant mass of air, the temperature of which is much higher than that of the air that surrounds it. Occlusion occurs when heat is displaced air mass and its separation from the surface of the earth. As a result, the front is mixed near the earth's surface already under the influence of two cold air masses. On the occlusion fronts, deep wave cyclones are often located, formed in the form of very chaotic wave disturbances. The wind at the same time increases significantly, and the wave becomes clearly expressed. As a result, the front of occlusion turns into a large blurred frontal zone and disappears completely after some time.

    Geographically, the fronts are divided into arctic, polar and tropical. Depending on the latitude in which they are formed. In addition, depending on the underlying surface, the fronts are divided into continental and sea.