Atmospheric front frontal zone is characterized. atmospheric front

At first glance, the air in the atmosphere appears to be stationary. In fact, movement occurs continuously in both vertical and horizontal directions. In motion, huge air masses interact with each other. Their dimensions are commensurate with the areas of the continents. This is the basis of such a phenomenon as an atmospheric front.

The air in such an array has uniform properties, obtained when it originates above the surface of the land or the ocean, where it was formed. Air vortices of the Earth move the air of the troposphere from one territory to another, transferring and changing their properties along with them. The behavior and properties of air masses determine the types of climate and weather features territory.

Classification of air masses

Depending on the properties, air masses are divided into types. The main classification criterion is the ratio of heat and moisture:

• cold and dry - the air of the Arctic and Antarctic;
• change the temperature and humidity according to the seasons of the year - polar (temperate latitudes);
• hot and dry - tropical;
• hot and humid - equatorial.

When moving, air masses collide, and atmospheric events rapidly develop on their border.

Atmospheric front - definition

Geography is a science that studies various natural phenomena. The concept of an atmospheric front is also considered here. It can be very extensive: several tens of kilometers long, hundreds of meters high and thousands of kilometers long. The transition zone from one property to another is called the frontal surface, and its intersection with the earth's surface is called the front line. It unfolds the main events, accompanied by sudden changes in the weather. The weather conditions will depend on what kind of air the front brought.

Thus, the atmospheric front in geography is the boundary between air masses of different properties.

difference atmospheric fronts from each other is determined not only by the temperature of the air, but also by how they originate.

warm front

It is formed when light warm air at a higher speed catches up with a cold mass, which, due to gravity, is not able to move quickly. Upon contact with cold air, warm air begins to creep up the gentle slope formed by the cold massif. Already two air masses together continue to move in the direction where the warm air moved. As the warm air rises, it cools and forms rain clouds.

A warm atmospheric front can always be recognized by the following features:

• barometers show a decrease in atmospheric pressure;
• there is an increase in air temperature;
• the harbingers of rain appear Spindrift clouds, gradually turning into cirrus-stratified, and then - into high-stratified;
• the wind intensifies, changing its direction;
• the clouds are filled with heaviness;
• precipitation falls.

Warming is a constant companion of the warm front. In summer, precipitation is prolonged, so rainy, albeit warm, weather sets in. In winter, the arrival of a warm front is associated with heavy snowfalls and thaws.

cold front

An atmospheric cold front occurs when cold air in motion, it catches up with warm, picks it up and quickly lifts it up. Due to its lightness, warm air quickly rises to a high altitude, and also cools quickly. Moisture from warm air turns into steam and forms clubs of cumulonimbus clouds. The air continues to move in the direction that the cold air moved. Always accompanied by showers and cooling.

Characteristic features of a cold front:

• there are pressure surges both behind the front line and in front of it;
• cumulus clouds appear;
• a squally wind is blowing, sharply changing direction from left to right;
• a downpour begins with a thunderstorm, hail is possible, precipitation can last several hours;
• it gets colder, the temperature difference can be up to 10 0 С;
• clearings are visible behind the cloud line.

The weather that accompanies a cold front is always a challenge, especially for those who are on the road.

Depending on the intensity of air movement, an atmospheric front of the 1st kind is distinguished, characterized by slow movement, and a front of the 2nd kind, moving rapidly and bringing rain and squally wind in summer, and snowfalls and blizzards in winter. They also differ in the speed of atmospheric processes taking place inside.

Fronts of occlusion

These are areas of connection of several fronts. They are also warm and cold. The mechanism of their formation is complex and depends on the properties of the air encountered. As a rule, two cold massifs and one warm massif participate in their formation, and vice versa.

With occlusion fronts, the following are observed:

• overcast and heavy rains;
• not an increase, but a change in wind direction;
• lack of jumps in atmospheric pressure;
• temperature constancy;
• the formation of cyclones.

Cyclones and anticyclones

Characteristic weather events during the passage of all types of fronts is impossible without mentioning cyclonic and anticyclonic types of weather.

Air over the surface of the planet is distributed unevenly, so it flows from where there is a lot of it to areas where there is not enough air. As a result, there is a difference in air pressure on the earth's surface. When air masses flow in the atmosphere, vortices are formed.

An air funnel with low pressure in the center is called a cyclone, and with high pressure - an anticyclone. Cloudy, snowy or rainy weather is called cyclonic, dry and clear weather is called anticyclonic, frosty in winter.

Geographic atmospheric differences

The geographical classification of atmospheric fronts is based on two features:

• geographic latitudes in which the formation of frontal zones occurs;
• front-forming (atmospheric) underlying surface.

On the border climatic zones, differing by dominant air masses, belts of frontal zones are formed. There are three of them on the globe:

1. In the polar zone of the Northern and Southern Hemispheres, at the border of cold polar and temperate air masses, the Arctic (in the Northern Hemisphere) and Antarctic (in the Southern Hemisphere) frontal zones formed.
2. An atmospheric polar front has formed between temperate and tropical latitudes. He encircles Earth in the region of the northern and southern tropics.
3. The tropical frontal zone is located on the border of tropical and equatorial air.

Depending on the season, the zones shift in the meridional direction. Circulation processes in geographic frontal zones form climatic zones.

Underlying surface and frontal zones

Dry continental air masses form over the continent, and wet sea masses form over the ocean. In the process of atmospheric circulation, they also collide, frontal zones are formed at the boundary, in which the properties of the air are transformed. Marine and continental atmospheric fronts are formed. The types of weather associated with them depend on the properties of the air.

So, we have dealt with such a concept as an atmospheric front, the definition of which is as follows - this is the line of contact of air masses different types. The properties of the atmospheric front depend on the direction in which the air masses move relative to each other. The passage of atmospheric fronts is always accompanied by a change weather conditions and atmospheric phenomena characteristic of each front.

Atmospheric fronts or simply fronts are transitional zones between two different air masses. The transition zone starts from the surface of the Earth and extends upward to the height where the differences between air masses are erased (usually to the upper limit of the troposphere). The width of the transition zone near the Earth's surface does not exceed 100 km.

In the transition zone - the zone of contact of air masses - there are sharp changes in the values meteorological parameters(temperature, humidity). Significant cloudiness is observed here, the most precipitation falls, the most intense changes in pressure, speed and wind direction occur.

Depending on the direction of movement of warm and cold air masses located on both sides of the transition zone, the fronts are divided into warm and cold. Fronts that change their position little are called inactive. A special position is occupied by occlusion fronts, which are formed when warm and cold fronts meet. Fronts of occlusion can be of the type of both cold and warm fronts. On weather maps, fronts are drawn either by colored lines or by symbols (see Fig. 4). Each of these fronts will be discussed in more detail below.

2.8.1. warm front

If the front moves in such a way that cold air recedes, giving way to warm air, then such a front is called warm. Warm air, moving forward, not only occupies the space where cold air used to be, but also rises up along the transition zone. As it rises, it cools and the water vapor in it condenses. As a result, clouds are formed (Fig. 13).

Figure 13. Warm front on the vertical section and on the weather map.

The figure shows the most typical cloudiness, precipitation and air currents of a warm front. The first sign of a warm front approaching will be the appearance of cirrus clouds (Ci). The pressure will start to drop. A few hours later, cirrus clouds, condensing, turn into a shroud of cirrus clouds. stratus clouds(Cs). Following the cirrostratus clouds, even denser high-stratus clouds (As) flow in, gradually becoming opaque to the moon or the sun. At the same time, the pressure drops more strongly, and the wind, turning slightly to the left, intensifies. Precipitation can fall from altostratus clouds, especially in winter, when they do not have time to evaporate along the way.

After some time, these clouds turn into nimbostratus (Ns), under which there are usually nimbus clouds (Frob) and nimbus clouds (Frst). Precipitation from nimbostratus clouds falls more intensely, visibility deteriorates, pressure drops rapidly, wind increases, often takes on a gusty character. When crossing the front, the wind turns sharply to the right, the pressure drop stops or slows down. Precipitation may stop, but usually they only weaken and turn into drizzle. The temperature and humidity of the air gradually increase.

Difficulties that may be encountered when crossing a warm front are mainly associated with a long stay in a zone of poor visibility, the width of which varies from 150 to 200 NM. It is necessary to know that the conditions of navigation in temperate and northern latitudes when crossing a warm front in the cold half of the year worsen due to the expansion of the zone of poor visibility and possible icing.

2.8.2. cold front

A cold front is a front moving towards a warm air mass. There are two main types of cold fronts:

1) cold fronts of the first kind - slowly moving or slowing down fronts, which are most often observed on the periphery of cyclones or anticyclones;

2) cold fronts of the second kind - fast moving or moving with acceleration, they arise during internal parts cyclones and troughs moving at high speed.

Cold front of the first kind. A cold front of the first kind, as was said, is a slowly moving front. In this case, warm air slowly rises up the wedge of cold air that invades under it (Fig. 14).

As a result, nimbostratus clouds (Ns) are first formed over the interface zone, passing at some distance from the front line into highly stratus (As) and cirrostratus (Cs) clouds. Precipitation begins to fall at the very front line and continues after it has passed. The width of the frontal precipitation zone is 60-110 nm. AT warm time In the forward part of such a front, favorable conditions are created for the formation of powerful cumulonimbus clouds (Cb), from which showers fall, accompanied by thunderstorms.

The pressure just before the front drops sharply and a characteristic “thunderstorm nose” is formed on the barogram - a sharp peak facing downwards. The wind turns towards it just before the passage of the front, i.e. makes a left turn. After the front passes, the pressure begins to increase, the wind turns sharply to the right. If the front is located in a well-defined hollow, then the wind turn sometimes reaches 180 °; for example, a southerly wind can be replaced by a northerly one. With the passage of the front comes a cold snap.

Rice. 14. Cold front of the first kind on a vertical section and on a weather map.

Sailing conditions when crossing a cold front of the first kind will be affected by poor visibility in the precipitation zone and squally winds.

Cold front of the second kind. This is a fast moving front. The rapid movement of cold air leads to a very intense displacement of prefrontal warm air and, as a consequence, to a powerful development of cumulus clouds (Cu) (Fig. 15).

Cumulonimbus clouds at high altitudes usually stretch forward 60-70 NM from the front line. This front part of the cloud system is observed in the form of cirrostratus (Cs), cirrocumulus (Cc), as well as lenticular altocumulus (Ac) clouds.

The pressure in front of the approaching front drops, but weakly, the wind turns to the left, and heavy rain falls. After the passage of the front, the pressure increases rapidly, the wind turns sharply to the right and increases significantly - it takes on the character of a storm. The air temperature sometimes drops by 10 ° C in 1-2 hours.

Rice. 15. Cold front of the second kind on a vertical section and on a weather map.

Navigation conditions when crossing such a front are unfavorable, since near the front line powerful ascending air currents contribute to the formation of a vortex with destructive wind speeds. The width of such a zone can be up to 30 NM.

2.8.3. Sedentary, or stationary, fronts

The front, which does not experience a noticeable shift either towards the warm or towards the cold air mass, is called stationary. Stationary fronts are usually located in a saddle or in a deep trough, or on the periphery of an anticyclone. The cloud system of a stationary front is a system of cirrostratus, altostratus and nimbostratus clouds, which looks approximately like a warm front. In summer, cumulonimbus clouds often form at the front.

The direction of the wind on such a front hardly changes. The wind speed on the side of cold air is less (Fig. 16). The pressure does not change significantly. In a narrow band (30 NM) heavy rain falls.

Wave disturbances can form on the stationary front (Fig. 17). The waves quickly move along the stationary front in such a way that the cold air remains on the left - in the direction of the isobars, i.e. in a warm air mass. The speed of movement reaches 30 knots or more.

Rice. 16. Sedentary front on the weather map.

Rice. 17. Wave disturbances on a sedentary front.

Rice. 18. The formation of a cyclone on a sedentary front.

After the passage of the wave, the front restores its position. Strengthening of the wave disturbance before the formation of a cyclone is observed, as a rule, if cold air is leaking from the rear (Fig. 18).

In spring, autumn, and especially summer, the passage of waves on a stationary front causes the development of intense thunderstorm activity, accompanied by squalls.

Navigation conditions when crossing a stationary front are complicated due to the deterioration of visibility, and in summer, due to the wind strengthening to a storm.

2.8.4. Fronts of occlusion

Occlusion fronts are formed as a result of the merging of cold and warm fronts and the displacement of warm air upwards. The closure process occurs in cyclones, where a cold front, moving at high speed, overtakes a warm one.

Three air masses are involved in the formation of an occlusion front - two cold and one warm. If cold air mass behind the cold front is warmer than the cold mass ahead of the front, then it, displacing warm air upwards, will simultaneously itself flow onto the front, colder mass. Such a front is called warm occlusion (Fig. 19).

Rice. 19. Front of warm occlusion on the vertical section and on the weather map.

If the air mass behind the cold front is colder than the air mass ahead of the warm front, then this rear mass will flow both under the warm and under the front cold air mass. Such a front is called cold occlusion (Fig. 20).

Occlusion fronts go through a number of stages in their development. The most difficult weather conditions on the fronts of occlusion are observed at the initial moment of closure of the thermal and cold fronts. During this period, the cloud system, as seen in Fig. 20 is a combination of warm and cold front clouds. Precipitation of a general nature begins to fall out of stratified-nimbus and cumulonimbus clouds, in the front zone they turn into showers.

The wind before the warm front of occlusion increases, after its passage it weakens and turns to the right.

Before the cold front of occlusion, the wind increases to a storm, after its passage it weakens and turns sharply to the right. As warm air is displaced into higher layers, the occlusion front gradually erodes, the vertical power of the cloud system decreases, and cloudless spaces appear. Nimbostratus cloudiness gradually turns into stratus, altostratus into altocumulus and cirrostratus into cirrocumulus. Rainfall stops. The passage of old fronts of occlusion is manifested in the flow of high-cumulus clouds of 7-10 points.

Rice. 20. Front of cold occlusion on a vertical section and on a weather map.

The conditions of navigation through the zone of the front of occlusion in the initial stage of development are almost the same as the conditions of navigation, respectively, when crossing the zone of warm or cold fronts.

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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 general properties 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 wind, chatter.

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. Heavy rainfall for middle lane Russia are caused by the impact of the polar dandy, which operates in July.

On a winter evening, when I was baking pancakes, my son Sasha and his friend Misha came running from the street. The children were delighted with warm weather they were playing snowballs. On TV, the announcer said that a warm atmospheric front had come to us. The boys asked me what is this atmospheric front? I had to explain everything to them.

What is an atmospheric front

I told the guys everything I knew about this phenomenon. Weather fronts occur when cold and warm air masses collide. They come to us from different places on the Earth, so the air masses are:

1. Arctic.
2. Polar.
3. Tropical.
4. Equatorial.

A warm atmospheric front brings a drop in pressure and heavy rainfall. And the air is getting warmer, like we have now.

A cold front in summer is accompanied by heavy rains, hail and wind. AT winter time brings snowstorms and squally winds.

The children were impressed by the photo of the cyclone, which can also occur under the action of atmospheric fronts.

What atmospheric fronts affect the climate of Russia

I told Sasha and Misha what atmospheric fronts are typical for our country. Usually we have an arctic and polar front, they arise in the Kara, Okhotsk and Barents Seas. Sasha remembered that in July in the middle lane, where we live, they go heavy rains, which interferes with the collection of cherries in the garden. I suggested that this could be explained by the influence of the polar front.

Misha said that Far East where they used to live, the climate is milder. I explained to the boy that there was a tropical front operating there.

The influence of atmospheric fronts on the climate of our planet

The climate on Earth is changing dramatically. Weather fronts now often bring snow in summer and warmth in winter. We can only adapt to global weather changes. Scientists suggest that soon the ocean may flood entire islands.

Luckily it doesn't happen in my area. strong hurricanes. But the climate has also changed. Now I try to cover the tomatoes in the beds with foil. AT open field they disappear due to sudden frosts or heat.

We have considered the types of atmospheric fronts. But when forecasting the weather in yachting, it should be remembered that the types of atmospheric fronts considered reflect only the main features of the development of a cyclone. In reality, there may be significant deviations from this scheme.
Signs of an atmospheric front of any type can in some cases be pronounced, or exacerbated, in other cases - weakly expressed, or blurry.

If the type of atmospheric front is sharpened, then when passing through its line, the air temperature and other meteorological elements change sharply, if it is blurred, the temperature and other meteorological elements change gradually.

The processes of formation and sharpening of atmospheric fronts are called frontogenesis, and the processes of erosion are called frontolysis. These processes are observed continuously, just as air masses are continuously formed and transformed. This must be remembered when forecasting the weather in yachting.

For the formation of an atmospheric front, it is necessary to have at least a small horizontal temperature gradient and such a wind field, under the influence of which this gradient would increase significantly in a certain narrow band.

A special role in the formation and erosion different types atmospheric fronts are played by baric saddles and the deformation fields of the wind associated with them. If the isotherms in the transition zone between adjacent air masses are parallel to the extension axis or at an angle of less than 45° to it, then they converge in the deformation field and the horizontal temperature gradient increases. On the contrary, if the isotherms are located parallel to the compression axis or at an angle of less than 45° to it, the distance between them increases, and if an already formed atmospheric front falls under such a field, it will be washed out.

Surface profile of the atmospheric front.

The slope angle of the surface profile of the atmospheric front depends on the difference in temperature and wind speed of warm and cold air masses. At the equator, atmospheric fronts do not intersect with the earth's surface, but turn into horizontal layers of inversion. It should be noted that the slope of the surface of a warm and cold atmospheric front is somewhat influenced by air friction on the earth's surface. Within the friction layer, the velocity of the frontal surface increases with height, and above the friction level it almost does not change. This has a different effect on the surface profile of a warm and cold atmospheric front.

When the atmospheric front began to move as a warm front, in the layer where the speed of movement increases with height, the frontal surface becomes more sloping. A similar construction for a cold atmospheric front shows that, under the influence of friction, the lower part of its surface becomes steeper than the upper one, and can even get a reverse slope below, so that warm air near the earth's surface can be located in the form of a wedge under the cold one. This complicates the prediction of future events in yachting.

Movement of atmospheric fronts.

An important factor in yachting is the movement of atmospheric fronts. The lines of atmospheric fronts on weather maps run along the axes of baric troughs. As is known, in a trough, the streamlines converge to the axis of the trough, and, consequently, to the line of the atmospheric front. Therefore, when passing it, the wind changes its direction rather sharply.

The wind vector at each point in front of and behind the atmospheric front line can be decomposed into two components: tangential and normal. For the movement of the atmospheric front, only the normal component of the wind speed matters, the value of which depends on the angle between the isobars and the front line. The speed of movement of atmospheric fronts can fluctuate over a very wide range, since it depends not only on the speed of the wind, but also on the nature of the pressure and thermal fields of the troposphere in its zone, as well as on the influence of surface friction. Determining the speed of movement of atmospheric fronts is extremely important in yachting when performing the necessary actions to avoid a cyclone.

It should be noted that the convergence of winds to the atmospheric front line in the surface layer stimulates upward air movements. Therefore, near these lines there are the most favorable conditions for the formation of clouds and precipitation, and the least favorable for yachting.

In the case of a sharp type of atmospheric front, a jet stream is observed above it and parallel to it in the upper troposphere and lower stratosphere, which is understood as narrow air flows with high speeds and large horizontal extent. Max Speed observed along the slightly inclined horizontal axis of the jet stream. The length of the latter is measured in thousands, width - hundreds, thickness - several kilometers. The maximum wind speed along the axis of the jet stream is 30 m/sec or more.

The emergence of jet streams is associated with the formation of large horizontal temperature gradients in high-altitude frontal zones, which, as is known, determine the thermal wind.

The stage of a young cyclone continues until warm air remains in the center of the cyclone near the earth's surface. The duration of this stage is on average 12-24 hours.

Zones of atmospheric fronts of a young cyclone.

Let us once again note that, as in the initial stage of the development of a young cyclone, warm and cold fronts are two sections of the wave-like curved surface of the main atmospheric front, on which the cyclone develops. In a young cyclone, three zones can be distinguished, which differ sharply in terms of weather conditions, and, accordingly, in terms of conditions for yachting.

Zone I - the front and central parts of the cold sector of the cyclone ahead of the warm atmospheric front. Here, the nature of the weather is determined by the properties of the warm front. The closer to its line and to the center of the cyclone, the more powerful the cloud system and the more probable precipitation is, the pressure drop is observed.

Zone II - the rear part of the cold sector of the cyclone behind the cold atmospheric front. Here the weather is determined by the properties of a cold atmospheric front and a cold unstable air mass. With sufficient humidity and significant instability of the air mass, showers fall. Atmosphere pressure grows behind his line.

Zone III - warm sector. Since a warm air mass is predominantly moist and stable, the weather conditions in it usually correspond to those in a stable air mass.

The figure above and below shows two vertical sections through the cyclone region. The upper one is made to the north of the center of the cyclone, the lower one is to the south and crosses all three considered zones. The lower one shows the rise of warm air in the front of the cyclone above the surface of the warm atmospheric front and the formation of a characteristic cloud system, as well as the distribution of currents and clouds near the cold atmospheric front in the rear of the cyclone. The upper section crosses the surface of the main front only in the free atmosphere; only cold air near the earth's surface, warm air flows over it. The section passes through the northern edge of the area of ​​frontal sediments.

The change in wind direction during the movement of the atmospheric front can be seen from the figure, which shows the streamlines of cold and warm air.

Warm air in a young cyclone moves faster than the disturbance itself moves. Therefore, more and more warm air flows through the compensation, descending along the cold wedge in the rear of the cyclone and ascending in its front part.

As the disturbance amplitude increases, the warm sector of the cyclone narrows: the cold atmospheric front gradually overtakes the slowly moving warm one, and there comes a moment when the warm and cold atmospheric fronts of the cyclone merge.

The central region of the cyclone near the earth's surface is completely filled with cold air, and warm air is pushed back into higher layers.