Atmospheric fronts. Atmospheric front Characteristics of atmospheric fronts

We looked at 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 pattern.
Signs of an atmospheric front of any type can in some cases be pronounced or aggravated, in other cases - weakly expressed or blurred.

If the type of atmospheric front is aggravated, 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 aggravation of atmospheric fronts are called frontogenesis, and the processes of erosion are called frontolysis. These processes are observed continuously, just as air masses. This must be remembered when forecasting the weather in yachting.

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

A special role in the formation and erosion of different types of atmospheric fronts is played by pressure saddles and associated wind deformation fields. If isotherms in the transition zone between neighboring air masses are located parallel to the stretch axis or at an angle of less than 45° to it, then in the deformation field they come closer and the horizontal temperature gradient increases. On the contrary, when 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.

Profile of the surface of the atmospheric front.

The angle of inclination 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 inversion layers. It should be noted that the amount of inclination of the surface of a warm and cold atmospheric front is somewhat influenced by air friction against earth's surface. Within the friction layer, the speed of movement of the frontal surface increases with height, and above the friction level it remains almost unchanged. This affects the surface profile of warm and cold atmospheric fronts differently.

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, and can even receive a reverse slope below, so that warm air at the earth’s surface can be located in the form of a wedge under the cold. This makes it difficult to predict subsequent 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 pressure troughs. As is known, in a trough, streamlines converge to the axis of the trough, and, consequently, to the line of the atmospheric front. Therefore, when passing through it, the wind changes its direction quite 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 an atmospheric front, only the normal component of wind speed is important, the value of which depends on the angle between the isobars and the front line. The speed of movement of atmospheric fronts can fluctuate within very wide limits, since it depends not only on the wind speed, 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 necessary actions on cyclone evasion.

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

In case sharp type atmospheric front above it and parallel to it in the upper troposphere and lower stratosphere, a jet stream is observed, which is understood as narrow air flows with high speeds and large horizontal extent. Maximum speed is noted along the slightly inclined horizontal axis of the jet stream. The length of the latter is measured in thousands, width - in hundreds, thickness - in 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, cause thermal wind.

The young cyclone stage continues as long as 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 note once again that, as in the initial stage of development of a young cyclone, the warm and cold front s represent two sections of the wavy curved surface of the main atmospheric front on which a cyclone develops. In a young cyclone, three zones can be distinguished, sharply differing in weather conditions, and, accordingly, in conditions for yachting.

Zone I is the front and central parts of the cold sector of the cyclone before the warm atmospheric front. Here the weather pattern 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 likely heavy precipitation is to fall, and a drop in pressure is observed.

Zone II is the rear part of the cold sector of the cyclone behind the cold atmospheric front. Here the weather is determined by the properties of the cold atmospheric front and the cold unstable air mass. With sufficient humidity and significant instability of the air mass, rainfall occurs. The atmospheric pressure behind its line is increasing.

Zone III - warm sector. Because a warm air mass is predominantly moist and stable, its weather conditions generally correspond to those of a stable air mass.

The figure above and below shows two vertical sections through the cyclone area. The upper one is made north of the center of the cyclone, the lower one is made to the south and crosses all three considered zones. The bottom shows the rise of warm air in the front part 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 part of the cyclone. The upper section intersects the surface of the main front only in the free atmosphere; There is only cold air at the earth's surface, warm air flows above it. The section passes through the northern edge of the region of frontal precipitation.

The change in wind direction as the atmospheric front moves can be seen from the figure, which shows the flow lines of cold and warm air.

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

As the amplitude of the disturbance increases, the warm sector of the cyclone narrows: the cold atmospheric front gradually catches up with the slowly moving warm one, and a moment comes when the warm and cold atmospheric fronts of the cyclone close together.

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

Atmospheric fronts have several various characteristics. According to them, this natural phenomenon is divided into different types.

Atmospheric fronts can reach a width of 500-700 km and a length of 3000-5000 km.

Atmospheric fronts are classified by their movement relative to the location of air masses. Another criterion is spatial extent and circulation significance. And finally, a geographical feature.

Characteristics of atmospheric fronts

Based on their movement, atmospheric fronts can be divided into cold, warm and occlusion fronts.
A warm atmosphere is formed when warm air masses, usually moist, move over drier and colder ones. Approaching warm front brings gradual decline atmospheric pressure, a slight increase in air temperature and light but prolonged precipitation.

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

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

Occlusion fronts arise when one atmospheric front superimposes on another, formed earlier. Between them there is a significant mass of air, the temperature of which is much higher than that of the air that surrounds it. Occlusion occurs when a warm air mass is displaced and separated from the surface of the earth. As a result, the front will mix at the surface of the earth under the influence of two cold air masses. On the occlusion fronts there are often deep wave cyclones formed in the form of very chaotic wave disturbances. At the same time, the wind increases significantly, and the wave becomes clearly defined. As a result, the occlusion front turns into a large blurred frontal zone and, after some time, completely disappears.

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

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

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

The main characteristic feature of atmospheric fronts is the large values ​​of horizontal gradients: pressure, temperature, humidity, etc. The zone of the atmospheric front is very narrow compared to the air masses it separates. When there is movement, the transition surface becomes inclined, with denser (cold) air forming a wedge under less dense (warm) air, and warm air sliding upward 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 as a single line. Only in large-scale vertical sections of the atmosphere is it possible to identify the upper and lower boundaries of the transition layer.

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

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

Fronts between the air masses of the above main geographical types called the main atmospheric fronts. The main fronts are: 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 sedentary (stationary), which can be primary, secondary and upper, as well as simple and complex (occluded). A special position is occupied by occlusion fronts, formed when warm and cold fronts close. Occlusion fronts can be either cold or warm fronts. On weather maps, fronts are drawn either as colored lines or as symbols.

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

A well-defined front has a height of several kilometers, most often 3-5 km. Major fronts are associated with prolonged and heavy precipitation; 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 not associated with fronts.

In the surface layer, due to the convergence of air flows to the axis of pressure troughs, the greatest contrasts in air temperature are created here - therefore, the fronts near the Earth are located precisely along the axes of pressure trenches. Fronts cannot be located along the axes of pressure ridges, where air flows diverge, but can only intersect the ridge axis at a large angle.

With height, the temperature contrasts on the axis of the pressure trough decrease - the axis of the trough shifts towards lower air temperatures and tends to align with the axis of the thermal trough, where temperature contrasts are minimal. Thus, with height, the front gradually moves away from the axis of the pressure 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 occlusion fronts, formed when warm and cold fronts close. Occlusion fronts can be either cold or warm fronts. On weather maps, fronts are drawn either as colored lines or as symbols.

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

Atmospheric fronts are inclined to the Earth's surface, their width reaches from 500 to 900 km, and their length extends to 2000-3000 km. In the frontal zones, an interface between two types of air appears: cold and warm. Such a surface is called frontal. As a rule, this surface is inclined towards the cold air - it is located under it, as it is heavier. 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 briefly called front.

Atmospheric front- a 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 an atmospheric front is always accompanied by precipitation.

Depending on the direction of movement, moving atmospheric fronts are divided into warm and cold. Warm front formed when warm air flows into cold air. The front line moves towards the cold air. After the passage of a warm front, warming occurs. A warm front forms a continuous line of clouds hundreds of kilometers long. There are lingering drizzling rains and warming is setting in. The rise of air during the arrival 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 front ()

It is formed when cold air flows under warm air, while the front line moves towards warm air, which is forced upward. Typically, a cold front moves very quickly. This causes strong winds, heavy, often heavy rainfall with thunderstorms, and snowstorms in winter. Cooling occurs after the passage of a cold front (see Fig. 3).

Rice. 3. Cold front ()

Atmospheric fronts can be stationary or moving. If air currents do not move towards either cold or warm air along the front line, such fronts are called stationary. If air currents have a speed of movement perpendicular to the front line, and move either towards cold or towards warm air, such atmospheric fronts are called moving. Atmospheric fronts arise, move and collapse in about a few days. The role of frontal activity in climate formation is more pronounced in temperate latitudes ah, that’s why most of Russia is characterized by unstable weather. 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

Zones reflecting their long-term positions are called climate fronts. On the border between Arctic and temperate air, over the northern regions of Russia, a arctic front. Air masses of temperate latitudes and tropical ones are separated by a polar temperate front, which is located mainly south of the borders of Russia. The main climate fronts do not form continuous stripes of lines, but are divided into segments. Long-term observations have shown that the Arctic and polar fronts move 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 northeast of it, 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 felt here. The branches of the polar climate front extend over southern territories our country only in summer; in winter they lie over Mediterranean Sea and Iran and occasionally capture the Black Sea.

Participate in the interaction of air masses cyclones And anticyclones- large moving atmospheric vortices that transport 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.

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

Rice. 5. Cyclone

Rice. 6. Anticyclone

The fronts on which cyclones and anticyclones originate are almost never straight; they are characterized by wave-like bends (see Fig. 7).

Rice. 7. Atmospheric fronts (synoptic map)

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

Rice. 8. Formation of an atmospheric vortex

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

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

Rice. 9. Air movement in an anticyclone

In Russia, cyclones and anticyclones are confined to the main climate fronts: polar and arctic. They also form on the border between marine and continental air masses of temperate latitudes. In western Russia, cyclones and anticyclones arise and move in the direction general transfer air from west to east. In the Far East in accordance with the direction of the monsoons. When moving with westerly transport 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 along northern regions Russia, and anticyclones - along the southern ones. In this regard, the atmospheric pressure in the north of Russia is lower, there may be inclement weather for many days in a row, in the south there is more sunny days, dry summer and little snowy winter.

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

Areas where intense winter cyclones pass: the Barents, Kara, Okhotsk Seas and the north-west of the Russian Plain. In summer, cyclones are most frequent on Far East and in the west of the Russian Plain. Anticyclonic weather prevails all year in the south of the Russian Plain, in the south Western Siberia, and in winter over the whole 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 influence it. Data on weather changes are plotted on special synoptic maps for further analysis weather conditions on the territory of our country.

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

Rice. 11. Synoptic map

Weather observations are carried out by an extensive network weather stations. The observation results are then transmitted to 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 flow atmospheric processes you can predict the weather. Accurate forecast weather is an extremely complex matter, since it is difficult to take into account the entire complex of interacting factors in their constant development. Therefore, even short-term forecasts of the hydrometeorological center are not always justified.

Source).).

Dust storm over the Arabian Sea ().

Cyclones and anticyclones ().

Homework

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

At first glance, it seems that the air in the atmosphere is motionless. In fact, the movement occurs continuously in both the vertical and horizontal directions. In motion, huge air masses interact with each other. Their sizes are comparable to the areas of the continents. This is the basis for such a phenomenon as an atmospheric front.

The air in such a mass has homogeneous properties obtained during its origin over the surface of the land or ocean where it was formed. Air vortices Earths move troposphere air 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 characteristics of the territory.

Classification of air masses

Depending on their 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 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 at 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 vast: several tens of kilometers in length, hundreds of meters in height and thousands of kilometers in length. The transition zone from one property to another is called the frontal surface, and its intersection with the surface of the earth is the front line. The main events unfold there, accompanied by sudden changes in weather. The weather situation will depend on what air the front brings.

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

The difference between atmospheric fronts and each other is determined not only by air temperature, but also by how they originate.

Warm front

It is formed when light warm air at a higher speed of movement catches up with a cold mass, which, due to gravity, is not able to move quickly. When it comes into contact with cold air, the 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 was moving. As the warm air rises, it cools and forms rain clouds.

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

• barometers show a decrease in atmospheric pressure;
• there is an increase in air temperature;
• harbingers of rain appear - cirrus clouds, gradually turning into cirrostratus, and then into altostratus;
• the wind intensifies, changing its direction;
• the clouds become heavy;
• precipitation falls.

Warming is a constant companion of a warm front. In summer, precipitation is prolonged, so inclement weather sets in, although warm weather. 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 catches up with warm air, picks it up and rapidly lifts it upward. Because of its lightness, warm air quickly reaches high altitudes and also cools quickly. Moisture from warm air turns into steam and forms clouds of cumulonimbus. The air continues its movement in the direction where the cold air moved. Always accompanied by rain and cold weather.

Characteristic signs of a cold front:

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

The weather that accompanies a cold front is always a challenge, especially for those 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 winds in summer, and snowfalls and blizzards in winter. They also differ in the speed of atmospheric processes taking place inside.

Occlusion fronts

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

At occlusion fronts the following are observed:

• overcast and continuous rain;
• not an increase, but a change in the direction of the wind;
• absence of atmospheric pressure surges;
• temperature constancy;
• formation of cyclones.

Cyclones and anticyclones

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

The 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 a high pressure - an anticyclone. Cyclonic is cloudy, snowy or rainy weather, anticyclonic - dry and clear, in winter - frosty.

Geographical atmospheric differences

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

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

On the border climatic zones, differing in the 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 southern hemisphere) frontal zones.
2. An atmospheric polar front formed between temperate and tropical latitudes. He girdles globe in the northern and southern tropics.
3. The tropical frontal zone is located at the boundary between tropical and equatorial air.

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

Underlying surface and frontal zones

Dry continental air masses form over the continent, and humid marine air masses form over the ocean. During atmospheric circulation, they also collide, and 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 changes in weather conditions and atmospheric phenomena characteristic of each front.