Atmospheric front - what is it? What is an atmospheric front Fronts of occlusion. Flight conditions

Air masses that differ in their physical properties are separated from each other by a layer of air called the frontal surface. In the layer of the frontal zone, temperature, humidity, density, and wind change sharply. The frontal zone is always inclined towards cold air. Above it is warm air, as less dense and light, and above it in the form of a wedge - cold. The main reason for the formation of fronts is the convergence of dissimilar air masses. The front is considered to be dynamically expressed if the temperature difference between warm and cold air is 8-10C for 1000 km distance. The speed of the front depends on the angle of intersection of the front with the isobars.

The fronts that separate the main geographic types of air masses are called main fronts.

Distinguish:

· the arctic front separating the arctic air from the air of temperate latitudes;

polar front separating temperate and tropical air;

a tropical front lying between tropical and equatorial air.

In terms of speed, these fronts can be stationary (the average speed of their movement is 5-10 km / h. They are located on the periphery of a cyclone or anticyclone), slow moving, fast moving. By temperature, warm, cold and occlusion fronts. According to the height of development - surface, tropospheric, high-altitude.

warm A front is a section of the main front moving towards cold air; warm air moves behind this front, which, being less dense, flows into cold air.

cold A front is a section of the main front moving towards warm air. Behind these fronts, cold air moves, which is denser and wedged under the warm air.

The front formed as a result of the merging of warm and cold air is called the front. occlusion.

3.3 Warm front in winter and summer. flight conditions.

At the warm front, warm air flows into the cold, located in the form of a wedge at the bottom. Ahead of the surface line, there is an area of pressure drop, which is due to the replacement of cold air with warm air. As the pressure drops, the wind increases, reaches its maximum speed before the passage of the front, then weakens. Winds of the southeast direction predominate ahead of the front, passing behind the front to the south and southwest.

The slow upward movement of warm air along the frontal surface leads to its adiabatic cooling and the formation of a cloud system and a large precipitation zone, the width of the cloud zone extends up to 600-700 km.

The slope of the frontal surface is observed within 1/100 to 1/200.

The main cloud system of the front is nimbostratus and highly stratified Ns-As clouds located in the lower and middle tiers (5-6 km). Their upper border is almost horizontal, and the lower one decreases from the front edge to the front line, where it reaches a height of about 100m (in cold weather it can be lower). Above As-Ns are cirrostratus and cirrus clouds. Sometimes they merge with the underlying cloud system. But often the clouds of the upper tier are separated from the Ns-As system by a cloud layer. A zone of extensive precipitation is observed under the main cloud system. It lies in front of the surface front line and has a length along the normal from the front up to 400 km.

In the precipitation zone, low broken-rain clouds with a lower boundary of 50-100 m are formed, sometimes frontal fogs occur, and ice is observed at temperatures from 0 to -3.

In winter, with strong winds, the passage of the front is accompanied by strong snowstorms. In summer, separate pockets of cumulonimbus clouds with showers and thunderstorms can appear on a warm front. Most often they occur at night. Their development is explained by the strong nighttime cooling of the upper layer of the main frontal cloud system at a relatively constant temperature in the lower layers of the cloud. This leads to an increase in temperature gradients and to an increase in vertical currents, which lead to the formation of cumulonimbus clouds. They are usually masked by nimbostratus clouds, which makes it difficult to visually identify them. When approaching nimbostratus clouds, inside which cumulonimbus are hidden, turbulence (turbulence) begins, increased electrization, which negatively affects the operation of instrumentation.

In winter, in the zone of negative temperatures of the warm front cloudiness, there is a danger of aircraft icing. The lower limit of icing is the zero isotherm. Heavy icing is observed in flight in the zone of supercooled rain. In the cold season, the warm front escalates and more often gives difficult weather conditions: low cloud cover, poor visibility in snowstorms, precipitation, fog, icing in precipitation, ice on the ground, electrification in the clouds.

Visibility after the passage of the front remains limited for some time, as the air is saturated with a large amount of moisture, which allows fogs, haze and low clouds to persist for a long time.

The temperature rises behind the warm front. On weather maps, a warm front is indicated by a red line.

3.4 Cold front of the 1st kind in winter and summer. flight conditions.

A cold front of the 1st kind moves at a speed of no more than 30 km/h.

In this case, there is an ordered slow rise of warm air along an invading wedge of cold air. In the cold half-year in the rising warm air, the process of condensation is not violent. As a result, nimbostratus clouds form over the frontal surface. Precipitation begins at the very front line, the width of the precipitation zone is 100-200 km.

In this season, the cloud system resembles the cloudiness of the warm front system, which is in reverse order. The clouds of the upper layer are located behind the surface front line and can be separated from the main cloud system by a cloudless layer.

The upper boundary of nimbostratus and altostratus clouds (Ns-As) is located at an altitude of 4-5 km.

In the warm season, cumulonimbus clouds of high vertical power form in front of the Ns-As cloud system, from which heavy precipitation occurs, accompanied by thunderstorms, these clouds are located in ridges along the front line with a width of 50-100 km. The upper limit can reach the tropopause and above. Under the clouds, showers, thunderstorms, squalls are observed. In the precipitation zone, low broken-rain clouds almost always form. The wind turns to the right after passing the front and weakens, the pressure in front of the front drops, behind the front it gradually increases, the temperature drops.

3.5 Cold front 2 types in winter and summer. flight conditions.

Fast moving cold front of the 2nd kind is the most dangerous of all types of atmospheric fronts. Due to the high speed of movement (40-50 km / h), cold air with great energy displaces warm air up to great heights. In summer, as a result of this strong dynamic convection, cumulonimbus clouds of high vertical power form in warm air, sometimes breaking through the tropopause. In the cold season

clouds are less powerful.

Cumulonimbus clouds are displaced forward in the direction of the wind at high altitudes, 100-300 km from the front line. Altocumulus lenticular clouds (Ac), which appear 200 km ahead of the surface front line, are a harbinger of the approach of such a front. Near the front line, cumulonimbus clouds are accompanied by squall eddies with destructive wind speeds and thunderstorms. The width of the cloud system reaches several tens of kilometers, the lower boundary is usually at a height of 300-400m, and in the precipitation zone it can drop to 100-200m.

In clouds, ascending currents with a force of up to 30 m/s or more and descending ones of up to 15 m/s or more present a great danger. In addition, there may be thunderstorms, heavy rainfall in the clouds, and intense icing in the zone of negative temperatures. But the width of this dangerous zone is small, about 50 km.

Near the ground, this front is accompanied by squalls, showers, thunderstorms, the width of the rainfall zone is several tens of kilometers and is usually observed ahead of the surface front line. The pressure in front of the front drops sharply, behind the front it grows rapidly. The wind after passing the front sharply changes direction to the right and increases to 20-30 m/s. The temperature behind the front drops by 10-12°C in 1 hour.

The weather is most pronounced on this front in the summer in the afternoon.

In winter, when the front passes, heavy snowfalls and blizzards are observed, which worsen visibility to several tens of meters. The main clouds are cumulonimbus (Cb) with an upper limit of 4-5 km.

Flights at flight level take place in simple weather conditions, and their main influence is manifested at low flight levels during takeoff, landing and climb.

3.6 Fronts of occlusion. flight conditions.

Warm and cold fronts are the fronts of young cyclones. A cold front, being more active and fast moving, usually catches up with a warm front and closes with it. At the same time, two cold air masses merge - located in front of the warm front and lying behind the cold front. The warm air trapped between the fronts is cut off from the ground and forced upward. The cloud systems of the warm and cold fronts converge and partially overlap each other and are also forced upward. This process is called the cyclone occlusion process, and the resulting front is called the occlusion front (occlusion - "occlusion" - lock close).

Occlusion results in two types of occlusion fronts:

1. warm front of occlusion (occlusion according to the type of warm front);

2. cold front of occlusion (cold front type occlusion).

Warm front of occlusion.

This front occurs if the cold air in the rear of the cyclone is a warmer air mass than the cold air in its front. When a cyclone is occluded, less cold air flows onto colder air, a multi-tiered cloud system is formed, consisting of a system of warm front clouds - stratus and cold front clouds - cumulonimbus, under which low fractured rain clouds can form.

Heavy precipitation begins ahead of the front line for 300-400 km, gradually turning into showers at the point of occlusion. The wind near the ground has a sharp right hand rotation and is getting stronger. The pressure drops quickly. Occlusions of this type are found mainly in the cold half of the year. At medium and high flight altitudes, aircraft may encounter masked cumulonimbus clouds, which cause severe turbulence and icing. The width of such a zone along the normal to the front is 50 km. When flying at low altitudes, there is always low cloudiness, turning into fog, icing, ice at the airfield..

Watching the weather changes is very exciting. The sun gives way to rain, the rain to snow, and gusty winds blow over all this diversity. 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 was given 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. 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, 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 consistent scientific system.

By definition, the inclined surface, which is the transition area 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 various 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 of a higher temperature, moving forward, is located in the territory where cold air masses dominated. 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;
heavy rain begins 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 are formed. High pressure zones are characterized by excess air, low - insufficient air. 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 form, they are divided geographically into:

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

Influence of the underlying surface

The physical properties of 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 movement of the masses 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.

), are separated from each other by rather narrow transition zones, which are strongly inclined to the 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, a sharp change in the weather is observed: it rises, changes direction by about 90 ° and weakens, visibility worsens, drizzling precipitation is formed.

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, strong winds occur. 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 of temperate latitudes, two temperate (polar) fronts separate the air of temperate latitudes 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.

The concept of an atmospheric front is commonly understood as a transition zone in which adjacent air masses with different characteristics meet. Fronts are formed when warm and cold air masses collide. They can stretch for tens of kilometers.

Air masses and atmospheric fronts

The circulation of the atmosphere occurs due to the formation of various air currents. Air masses located in the lower layers of the atmosphere are able to combine with each other. The reason for this is the common properties of these masses or identical origin.

Changes in weather conditions occur precisely because of the movement of air masses. Warm temperatures cause warming, and cold temperatures cause cooling.

There are several types of air masses. They are distinguished by the origin. Such masses are: arctic, polar, tropical and equatorial air masses.

Atmospheric fronts occur when various air masses collide. Collision areas are called frontal or transitional. These zones instantly appear and also quickly collapse - it all depends on the temperature of the colliding masses.

The wind generated during such a collision can reach speeds of 200 km/k at an altitude of 10 km from the earth's surface. Cyclones and anticyclones are the result of collisions of air masses.

Warm and cold fronts

Warm fronts are fronts moving in the direction of cold air. The warm air mass moves along with them.

As warm fronts approach, pressure decreases, clouds thicken, and heavy precipitation falls. After the front has passed, the direction of the wind changes, its speed decreases, the pressure begins to gradually rise, and the precipitation stops.

A warm front is characterized by the flow of warm air masses onto cold ones, which causes them to cool.

It is also often accompanied by heavy rainfall and thunderstorms. But when there is not enough moisture in the air, precipitation does not fall.

Cold fronts are air masses that move and displace warm air. A cold front of the first kind and a cold front of the second kind are distinguished.

The first genus is characterized by the slow penetration of its air masses under warm air. This process forms clouds both behind the front line and within it.

The upper part of the frontal surface consists of a uniform cover of stratus clouds. The duration of the formation and decay of a cold front is about 10 hours.

The second kind is cold fronts moving at high speed. Warm air is instantly displaced by cold air. This leads to the formation of a cumulonimbus region.

The first signals of the approach of such a front are high clouds, visually resembling lentils. Their education takes place long before his arrival. The cold front is located two hundred kilometers from the place where these clouds appeared.

The cold front of the 2nd kind in the summer is accompanied by heavy precipitation in the form of rain, hail and squally winds. Such weather can spread for tens of kilometers.

In winter, a cold front of the 2nd kind causes a snow blizzard, strong winds, and turbulence.

Atmospheric fronts of Russia

The climate of Russia is mainly influenced by the Arctic Ocean, the Atlantic and the Pacific.

In summer, Antarctic air masses pass through Russia, affecting the climate of Ciscaucasia.

The entire territory of Russia is prone to cyclones. Most often they form over the Kara, Barents and Okhotsk Seas.

Most often in our country there are two fronts - the Arctic and the Polar. They move south or north during different climatic periods.

The southern part of the Far East is subject to the influence of the tropical front. Abundant precipitation in central Russia is caused by the influence of the polar front, which operates in July.

The lower part of the Earth's atmosphere, the troposphere, is in constant motion, shifting over the surface of the planet and mixing. Its individual sections have different temperatures. When such atmospheric zones meet, atmospheric fronts arise, which are boundary zones between air masses of different temperatures.

Formation of an atmospheric front

The circulation of tropospheric currents causes warm and cold air currents to meet. At the place of their meeting, due to the temperature difference, active condensation of water vapor occurs, which leads to the formation of powerful clouds, and subsequently to heavy precipitation.

The boundary of atmospheric fronts is rarely even, it is always tortuous and inhomogeneous, due to the fluidity of air masses. Warmer atmospheric currents flow on cold air masses and rise up, colder ones displace warm air, forcing it to rise higher.

Rice. 1. Approach of the atmospheric front.

Warm air is lighter than cold air and always rises, cold air, on the contrary, accumulates near the surface.

Active fronts move at an average speed of 30-35 km. per hour, but they can temporarily stop their movement. Compared with the volume of air masses, the boundary of their contact, which is called the atmospheric front, is very small. Its width can reach hundreds of kilometers. In length - depending on the magnitude of the colliding air currents, the front can be thousands of kilometers long.

Signs of a weather front

Depending on which atmospheric current moves more actively, warm and cold fronts are distinguished.

Weather and atmospheric front

In areas where atmospheric fronts pass, the weather changes.

Rice. 3. Collision of warm and cold air currents.

Its changes depend on:

temperatures of the air masses encountered . The greater the temperature difference, the stronger the winds, the more intense the precipitation, the more powerful the clouds. And vice versa, if the temperature difference of air currents is small, then the atmospheric front will be weakly expressed and its passage over the Earth's surface will not bring any special weather changes;
air current activity . Depending on their pressure, atmospheric flows can have different speeds of movement, on which the rate of weather change will depend;
front shapes . The simpler linear forms of the front surface are more predictable. With the formation of atmospheric waves or the closure of individual outstanding tongues of air masses, vortices are formed - cyclones and anticyclones.

After the passage of a warm front, weather with a higher temperature sets in. After the passage of the cold - there is a cooling.

What have we learned?

Atmospheric fronts are border areas between air masses with different temperatures. The greater the temperature difference, the more intense the weather change will be during the passage of the front. The approach of a warm or cold front can be distinguished by the shape of the clouds and the type of precipitation.

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