What is an atmospheric front? Atmospheric fronts. Reasons for education

Air masses move around the planet as a whole. Atmospheric fronts, or simply fronts, are transition zones between two different air masses. Transition zones between adjacent air masses with different properties are called atmospheric fronts... The main characteristic feature of atmospheric fronts are large values ​​of horizontal gradients: pressure, temperature, humidity and others. Significant cloudiness is observed here, the most precipitation falls, the most intense changes in pressure, strength and direction of the wind occur.

An atmospheric front arises when masses of cold and warm air approach and meet in the lower layers of the atmosphere or throughout the troposphere, covering a layer with a thickness of up to several kilometers, with the formation of an inclined interface between them.

The main characteristic feature of atmospheric fronts is large values ​​of horizontal gradients: pressure, temperature, humidity, etc. The zone of the atmospheric front is very narrow in comparison with the air masses it separates. In the presence of motion, the transition surface becomes inclined, while the denser air (cold) forms a wedge under the less dense (warm) air, and the warm air makes an upward sliding along this wedge.

The vertical thickness of the frontal surface is very small - several hundred meters, which is much less than the width of the air masses that it separates. Within the troposphere, one air mass overlaps another. The width of the front zone on weather maps is several tens of kilometers, but when analyzing synoptic maps, the front is drawn in the form of a single line. Only on vertical sections of the atmosphere on a large scale is it possible to reveal the upper and lower boundaries of the transition layer.

For this reason, on synoptic maps, fronts are depicted as a line (front line). At the intersection with the earth's surface, the front zone is about ten kilometers wide, while the horizontal dimensions of the air masses themselves are about thousands of kilometers.

In the horizontal direction, the length of the fronts, like the air masses, has thousands of kilometers, along the vertical - about 5 km, the width of the frontal zone to the Earth's surface is about a hundred kilometers, at heights - several hundred kilometers. Frontal zones are characterized by significant changes in air temperature and humidity, wind directions along the horizontal surface, both at ground level and above.

The fronts between air masses of the above basic geographic types are called main atmospheric fronts. Main fronts: arctic (between arctic and polar air), polar (between polar and tropical air) and tropical (between tropical equatorial air).

According to thermodynamic properties, atmospheric fronts between air masses of the same geographic type are divided into warm, cold and inactive (stationary), which can be primary, secondary and upper, as well as simple and complex (occluded). A special position is occupied by the fronts of occlusion, formed during the closure of the warm and cold fronts. Occlusion fronts can be either cold or warm fronts. On weather maps, fronts are drawn either with colored lines or in the form of symbols.

Complex complex fronts - occlusion fronts are formed by the closing of cold and warm fronts during the occlusion of cyclones. A distinction is made between a warm front of occlusion, if the air behind the cold front is warmer than the air ahead of the warm front, and a cold front of occlusion, when the air behind the cold front is colder than the air ahead of the warm front.

A well-defined front has a height of several kilometers, most often 3-5 km. Prolonged and heavy rainfall is associated with the main fronts; in the system of secondary fronts, cloud formation processes are less pronounced, precipitation is short-lived and does not always reach the Earth. There are also intramass precipitations that are not associated with fronts.

In the surface layer, due to the convergence of air flows to the axis of the baric troughs, the greatest contrasts in air temperature are created here - therefore, the fronts at the Earth are located exactly along the axes of the baric troughs. The fronts cannot be located along the axes of the baric ridges, where there is a divergence of air flows, but can only intersect the ridge axis at a large angle.

The temperature contrasts on the axis of the baric trough decrease with height - the axis of the trough shifts towards lower air temperatures and tends to align with the axis of the thermal trough, where the temperature contrasts are minimal. Thus, with height, the front gradually moves away from the axis of the baric trough to its periphery, where the greatest contrasts are created.

Depending on the direction of movement of warm and cold air masses located on both sides of the transition zone, fronts are divided into warm and cold. Fronts that change their position little are called sedentary. A special position is occupied by the fronts of occlusion, formed during the closure of the warm and cold fronts. Occlusion fronts can be either cold or warm fronts. On weather maps, fronts are drawn either with colored lines or in the form of symbols.

The weather in our country is unstable. This is especially evident in the European part of Russia. This is due to the fact that there are different air masses: warm and cold. Air masses differ in properties: temperature, humidity, dustiness, 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 towards the Earth's surface, their width reaches from 500 to 900 km, and in length they extend for 2000-3000 km. 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 the cold air - as it is heavier, it is located under it. 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 Earth's surface forms front line, which is also called briefly front.

Atmospheric front- transition zone between two dissimilar air masses.

Warm air, being lighter, rises. As it rises, it cools and becomes saturated with water vapor. Clouds form in it and precipitation falls. Therefore, the passage of the 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. In this case, the front line moves towards the cold air. After the passage of the warm front, warming sets in. The warm front forms a continuous strip of clouds hundreds of kilometers long. There are prolonged drizzling rains, and warming sets in. 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 flows under the warm one, while the front line moves towards the warm air, which is displaced upward. As a rule, the cold front moves very quickly. This causes strong winds, heavy, often heavy rainfall with thunderstorms, and snowstorms in winter. After the passage of the cold front, a cold snap sets in (see fig. 3).

Rice. 3. Cold front ()

Atmospheric fronts are stationary and moving. If the air currents do not move towards either cold or warm air along the front line, such fronts are called stationary... If the air currents have a speed of movement perpendicular to the front line, and move either towards cold or 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 arise when the main types of air masses come into contact: arctic, temperate, tropical (see fig. 4).

Rice. 4. Formation of atmospheric fronts on the territory of Russia

The zones reflecting their long-term positions are called climatic fronts... On the border between the arctic and temperate air, over the northern regions of Russia, a Arctic front. The air masses of temperate and tropical latitudes are divided by the polar temperate front, which is located mainly south of the borders of Russia. The main climatic fronts do not form continuous stripes of lines, but are divided into segments. Long-term observations have shown that the Arctic and polar fronts shift to the south in winter and north in summer. In the east of the country, the Arctic front reaches the coast of the Sea of ​​Okhotsk in winter. To the north-east of it, a very cold and dry arctic air prevails. In European Russia, the Arctic front does not move that far. The warming effect of the North Atlantic Current is here. The branches of the polar climatic front stretch over the southern territories of our country only in summer, in winter they run over the Mediterranean Sea and Iran and occasionally capture the Black Sea.

The interaction of air masses is attended by cyclones and anticyclones- large moving atmospheric vortices carrying atmospheric masses.

An area of ​​low atmospheric pressure with a specific system of winds blowing from the edges to the center and deviating counterclockwise.

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

The cyclones are impressive in size, extending into the troposphere to a height of 10 km, and a width of up to 3000 km. In cyclones, the pressure increases, and in anticyclones, it decreases. In the northern hemisphere, the winds blowing towards the center of the cyclones are deflected under the influence of the force of the axial rotation of the earth to the right (the air swirls 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 arise are almost never rectilinear, they are characterized by undulating bends (see fig. 7).

Rice. 7. Atmospheric fronts (synoptic map)

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

Rice. 8. Formation of atmospheric vortex

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

Atmospheric vortices live up to destruction for 5-10 days. And the intensity of their formation depends on the properties of the underlying surface (temperature, humidity). Several cyclones and anticyclones are formed in the troposphere every day. Hundreds of them are formed during 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. Cloudless dry weather, hot in summer and frosty in winter, prevails during the entire time of the anticyclone. This is facilitated by the slow descent 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, complete calm is observed - calm(see fig. 9).

Rice. 9. Air movement in the anticyclone

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

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

Areas of intense winter cyclones: the Barents, Kara, Okhotsk Seas and the northwest of the Russian Plain. In summer, cyclones are most frequent in the Far East and in the west of the Russian Plain. Anticyclonic weather prevails all year round 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 applied to special synoptic maps for further analysis of weather conditions on the territory of our country.

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

Rice. 11. Synoptic chart

Weather observations are carried out by an extensive network of meteorological stations. The observation results are then transmitted to the hydrometeorological data centers. Here they are processed, and weather information is plotted on synoptic maps. The maps show atmospheric pressure, fronts, air temperature, wind direction and speed, cloud cover and precipitation. The distribution of atmospheric pressure indicates the position of cyclones and anticyclones. Having studied the patterns of atmospheric processes, you can predict the weather. An accurate weather forecast is an extremely difficult 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 do not always come true.

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Homework

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

), are separated from each other by rather narrow transition zones, which are strongly inclined to the earth's surface (less than 1 °). front is called the division between those with 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 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.

There are fronts associated with cyclones and climatic fronts.

In cyclones, fronts are formed when warm and cold air meet, with the top of the frontal system, as a rule, located in the center. Cold air, meeting warm air, is always below. He leaks under the warm, trying to force it up. Warm air, on the contrary, flows into cold air and if it oppresses it, then it itself rises along the separation plane. Depending on which air is more active, in which direction the front shifts, it is called warm or cold.

The warm front moves towards the cold air and means the onset of warm air. He slowly drives back the cold air. As a lighter one, it flows onto a wedge of cold air, gently rising upward along the interface. In this case, a vast zone of clouds forms ahead of the front, from which overburden precipitation falls. The strip of precipitation ahead of the warm front reaches 300, and even 400 km in cold weather. Behind the front line, precipitation stops. The gradual change of cold air to warm air leads to a decrease in pressure and an increase in wind. After passing the front, a sharp change in weather is observed: it rises, changes direction by about 90 ° and weakens, visibility deteriorates, drizzling precipitation forms, and may fall.

The cold front moves towards the warm air. In this case, cold air - as 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. Large cumulonimbus forms above and in front of the front line, from which heavy rains fall, strong winds occur and are observed. After the front passes, precipitation and cloudiness decrease significantly, the wind changes direction by about 90 ° and weakens somewhat, the temperature decreases, the air humidity decreases, its transparency and visibility increase; growing.

The Arctic (Antarctic) front separates the Arctic (Antarctic) air from the air of temperate latitudes, two moderate (polar) fronts separate the air of temperate latitudes and tropical air. A tropical front forms where tropical and air meet, differing in temperature rather than temperature. All fronts, together with the boundaries of the belts, shift towards the poles in summer and in winter. Often they form separate branches, spreading over long distances from. The tropical front is always in the hemisphere where summer is.

Watching the weather changes is very exciting. The sun gives way to rain, rain to snow, and gusty winds blow over all this diversity. In childhood, this causes admiration and surprise, in older people - the 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 line on which the clash of enemy forces occurs. And the concept of atmospheric fronts is the boundaries of contact of two air masses, which are formed 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. The troposphere - the lower part of the Earth's atmosphere - provides us with oxygen and is in constant motion. It all consists of separate air masses, united by a common occurrence and similar indicators. Among the main indicators of these masses, volume, temperature, pressure and humidity are determined. During movement, different masses can come closer and collide. However, they never lose their boundaries and do not mix with each other. - these are areas where sharp weather jumps occur and come into contact.

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 Norwegian's research, back in 1863, Admiral Fitzroy suggested that violent atmospheric processes begin at the meeting points of air masses coming from different parts of the world. But at that moment, the scientific community did not pay attention to 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 coherent scientific system.

By definition, an inclined surface that represents the transition area between different air flows is called a frontal surface. But atmospheric fronts are a mapping of frontal surfaces to a meteorological map. Usually, the transitional region of the atmospheric front is tied up at the Earth's surface and rises up to those heights at which the differences between the 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 point where different fronts meet. Let's take a closer look at 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 of a higher temperature, moving forward, is located in the territory where cold air masses prevailed. In addition, it rises upward 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 a warm atmospheric front can be determined:

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

Usually, after the precipitation stops, it gets warmer, but this does not last long, since the cold front moves very quickly and catches up with the warm atmospheric front.

Cold front

Such a feature is observed: the warm front is always inclined towards the direction of motion, and the cold front is always inclined towards the opposite. When the 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 down, moisture condenses into clouds.

The main signs by which a cold front can be determined:

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

For travelers, going through the cold front is not an easy test. Sometimes it is necessary to overcome whirlwinds and squalls in poor visibility conditions.

Front of occlusions

It has already been said that atmospheric fronts are different, if everything is more or less clear with warm and cold, then the front of occlusions raises a lot of questions. The formation of such effects occurs in the places where the cold and warm fronts meet. Warmer air is then forced upward. The main action takes place in cyclones at the moment when a more impetuous cold front overtakes 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 signs by which you can determine the front of occlusions:

• overburden clouds and precipitation;
• abrupt changes without a strong change in speed;
• smooth pressure change;
• lack of sudden temperature changes;
• cyclones.

The front of the occlusions depends on the temperature of the cold air masses in front of it and behind its line. Distinguish between cold and warm occlusion fronts. The most difficult conditions are observed at the moment of the immediate closing of the fronts. As the warm air is displaced, the front erodes and improves.

Cyclone and anticyclone

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

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

An anticyclone is a high-pressure area that displaces excess air into low-pressure zones. The main characteristic is clear weather, since clouds are also forced out of this zone.

Geographic separation of atmospheric fronts

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

1. Arctic, separating cold arctic air masses from moderate 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

The physical properties of air masses are influenced by radiation and the appearance of the Earth. Since the nature of such a surface can be different, then the friction against it is uneven. Difficult geographic landforms can deform the front line and change its effects. For example, there are known cases of destruction of atmospheric fronts when transshipping over mountain ranges.

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

It turned out that warm air is drawn into the cyclone not along its entire eastern (right) half, but in a rather limited sector located in the southern and southeastern parts of the cyclone between two convergence lines. Cloudiness and precipitation are unevenly distributed in the cyclone. Heavy rains fall mainly in front of the first (eastern) convergence line of air currents, as well as in the center of the cyclone. Heavy rains and thunderstorms are concentrated in a narrow strip along the second (western) convergence line. These lines were later called atmospheric fronts. Since cyclones usually move from west to east in temperate latitudes, the eastern front of the cyclone first passes through the observation point, followed by warm air. This atmospheric front was called warm. In the vicinity of a warm atmospheric front, warm air actively advances on the front line, moves almost perpendicular to it, and cold air is transported almost parallel to this line, i.e. slowly backs away from her. Consequently, the warm air mass catches up and surpasses the cold one. Then the western (cold) front of the cyclone approaches the observation point, during the passage of which the air temperature drops sharply. Near the cold atmospheric front, the dynamics are different: cold air catches up with warm air and rapidly displaces it upward.

The upward sliding covers thick layers of warm air over the entire frontal surface, and an extensive system of high-stratus - nimbo-stratus clouds with massive precipitation arises. The warm front has an anticyclonic curvature and moves towards the cold air. On the weather map, a warm front is marked in red or blackened semicircles directed towards the front's movement (Fig. 1). As the line of the warm front approaches, the pressure begins to drop, clouds are condensed, and heavy precipitation falls. In winter, when the front passes, low stratus clouds usually appear. Temperature and humidity rise slowly. When the front passes, temperature and humidity usually rise rapidly, and the wind intensifies. After the front passes, the wind direction changes (the wind turns clockwise), its speed decreases, the pressure drop stops and its weak growth begins, the clouds dissipate, precipitation stops. The field of baric tendencies is presented as follows: a closed region of pressure drop is located in front of the warm front, behind the front there is either an increase in pressure or a relative increase (a drop, but less than before the front). The passage of a warm front is usually accompanied by a powerful stratus-rain cloud covering the entire sky with heavy rain. The first messenger of the warm front is cirrus clouds. Gradually they turn into a solid white veil into cirrostratus clouds. Warm air is already moving in the upper atmosphere. Pressure drops. The closer the front line is to us, the denser the clouds become. The sun shines through with a dull spot. Then the clouds descend below, the sun disappears completely. The wind intensifies and changes its direction clockwise (for example, at first there was east, then south-east and even south-west) Approximately 300-400 km before the front, the clouds thicken. Light heavy rain or snow begins. But now the warm front has passed. The rain or snow has stopped, the clouds dissipate, warming sets in - a warmer air mass has come. The warm front in vertical section is shown in Fig. 2.

If warm air recedes, and cold air spreads after it, then a cold front is approaching. His arrival always causes a cold snap. But when moving, not all layers of air have the same speed. The lowest layer, as a result of friction against the earth's surface, is slightly delayed, and the higher ones are pulled forward. Thus, cold air falls on warm air in the form of a roll. Warm air is quickly forced upward, and powerful accumulations of cumulus and cumulonimbus clouds are created. Cold front clouds carry showers, thunderstorms, accompanied by strong gusty winds. They can reach very high heights, but in the horizontal direction they extend only 20 ... 30 km. And since the cold front usually moves quickly, the stormy weather does not last long - from 15 ... 20 minutes. up to 2 ... 3 hours. As a result of the interaction of cold air with a warm underlying surface, cumulus clouds with gaps are formed. Then comes full clarification.

In the case of a cold front, the upward movement of warm air is limited to a narrower zone and especially strongly ahead of the cold wedge, where warm air is forced out by cold air. The clouds here will largely have the character of cumulonimbus with showers and thunderstorms (Fig. 3, Fig. 4). The cold front has a cyclonic curvature (bulge towards warm air) and moves towards warm air. On the weather map, the cold front is marked in blue or blackened triangles directed in the direction of the front movement (Fig. 1). The flow in cold air has a component directed towards the front line, therefore, the cold air, moving forward, occupies the space where the warm air was previously, which increases its instability.

When crossing the line of a warm front, the wind, as in the case of a warm front, turns to the right, but the turn is more significant and sharp - from the southwestern, southern (in front of the front) to the western, northwestern (behind the front). This increases the wind speed. The atmospheric pressure ahead of the front changes slowly. It can fall, but it can grow. With the passage of the cold front, a rapid increase in pressure begins. A closed isallobaric region of pressure growth is located behind the cold front, and the growth can reach 3-5 hPa / 3 h. A change in pressure in the direction of its growth (from a fall to an increase, from a slow growth to a stronger one) indicates the passage of the surface front line.

Thunderstorms and squalls are often observed ahead of the front. The air temperature after passing the front drops, and often quickly and sharply - by 10 ° C or more in 1-2 hours. The mass fraction of water vapor decreases simultaneously with the air temperature. Visibility tends to improve as polar or arctic air invades behind the cold front. In addition, the instability of the air mass prevents condensation near the Earth's surface.

The nature of the weather on a cold front differs markedly depending on the speed of the front displacement, the properties of warm air ahead of the front, and the nature of the ascending movements of warm air above the cold wedge. On cold fronts of the 1st kind, the orderly rise of warm air above the wedge of cold air predominates. A cold front of the 1st kind is a passive upward sliding surface. Slow-moving or slowing-down fronts belong to this type, mainly at the periphery of cyclonic regions in deep baric troughs. In this case, the clouds are located mainly behind the front line. The difference from the cloudiness of the warm front still exists. Due to friction, the surface of the cold front in the lower layers becomes steep. Therefore, just before the front line, instead of a calm and gentle upward sliding, a steeper (convective) rise of warm air is observed (Fig. 3). Due to this, powerful cumulus and cumulonimbus clouds sometimes appear in the front of the cloud system, stretching for hundreds of kilometers along the front, with showers in summer, snowfalls in winter, thunderstorms, hail and squalls. Above the overlying part of the frontal surface with a normal inclination as a result of the upward sliding of warm air, the cloud system represents a uniform cover of stratus clouds. Heavy rainfall ahead of the front, after the front has passed, is replaced by more uniform overburden rainfall. Finally, cirrostratus and cirrus clouds appear. In this case, the vertical thickness of the system and the width of the cloud system and the precipitation area will be almost 2 times less than in the case of a warm front. The upper boundary of the system is located approximately at an altitude of 4-4.5 km. Stratus ruptured clouds can appear under the main cloud system, sometimes frontal fogs are formed. The duration of the passage of the 1st type cold front through the observation point is 10 hours or more.

The fronts of the second kind in the lower atmosphere are the passive surface of the upward slip, and above it, the active surface of the downward slip. Most of the rapidly moving cold fronts in cyclones belong to this type. Here, the warm air of the lower layers is displaced upward by a cold roll advancing forward. The surface of the cold front in the lower layers is very steep, even forming a bulge in the form of a shaft (Fig. 4). The rapid movement of the cold air wedge causes forced convection of the displaced warm air in a narrow space at the front of the front surface. Here, a powerful convective flow is created with the formation of cumulonimbus clouds, which intensifies as a result of thermal convection. The forerunners of the front are altocumulus lenticular clouds, which spread in front of it at a distance of up to 200 km. The emerging cloud system has a small width (50-100 km) and does not represent separate convective clouds, but a continuous chain, or a cloud bank, which sometimes may not be continuous. In the warm half of the year, the upper limit of cumulonimbus clouds extends to the height of the tropopause. On cold fronts of the 2nd kind, there is intense thunderstorm activity, showers, sometimes with hail, squally winds. There is a lot of turbulence and icing in the clouds. The width of the zone of dangerous weather phenomena is several tens of kilometers. In the cold half of the year, the tops of cumulonimbus clouds reach 4 km. The width of the snowfall zone is 50 km. This cloudiness is associated with heavy snowfalls, blizzards with visibility less than 1000 m, a sharp increase in wind speed, turbulence.

When cold fronts of the 2nd kind pass through the observation point, first (3-4 hours before the front line near the Earth) cirrus clouds appear, which are quickly replaced by highly layered, sometimes lenticular, which are quickly replaced by a bulk with showers, thunderstorms, hail, squalls. The duration of the movement of a cloud system with heavy rainfall and thunderstorms usually does not exceed 1-2 hours. After the passage of the cold front, heavy rainfall stops. A feature of cold fronts of both the first and second kind are prefrontal squalls. Since in the front part of the cold wedge, due to friction, a steep slope of the front surface is created, part of the cold air is above the warm one. Further, cold air masses “collapse” downward in the front part of the advancing cold shaft. The collapse of cold air leads to the displacement of warm air upward and to the emergence of a vortex with a horizontal axis along the front. Squalls on land are especially intense in summer, with a large temperature difference between warm and cold air on both sides of the front and with instability of warm air. Under these conditions, the passage of the cold front is accompanied by destructive wind speeds. Wind speed often exceeds 20-30 m / s, the duration of the phenomenon is usually several minutes, sometimes gusts are observed.

Occlusion fronts
Due to the downward movements in the cold air in the rear of the cyclone, the cold front moves faster than the warm front and eventually overtakes it. At the stage of filling the cyclone, complex fronts arise - the fronts of occlusion, which are formed when the cold and warm atmospheric fronts converge.

In the occlusion front system, three air masses interact, of which the warm one no longer touches the Earth's surface. The process of displacing warm air into the upper layers is called occlusion. In this case, the rear wedge of cold air of the cyclone closes with the front wedge of cold air. Warm air in the form of a funnel gradually rises up, and its place is taken by cold air coming from the sides (Fig. 5). The interface that occurs when the cold and warm fronts meet is called the occlusion front surface.

In the case of a cold front of occlusion, precipitation can fall on both sides of the lower front, and the transition from overburden to heavy rainfall, if any, occurs not in front of the lower front, but in the immediate vicinity of it. In the case of a warm occlusion front, the warm air funnel is displaced by the warmer air flowing onto the colder air wedge. The rear wedge of less cold air catches up with the front wedge of colder air, and the cold front, having separated from the surface of the Earth, rises along the surface of the warm front.

A weak upward sliding of the rear air along the anterior surface along the occlusion surface can lead to the formation of St-Sc-type clouds along it, which do not reach the level of ice cores. Drizzling precipitation will fall from them in front of the lower warm front.