Yachting. Weather. Atmospheric front - formation and erosion. Atmospheric front Formation of atmospheric fronts

Atmospheric front, tropospheric fronts - a transitional zone in the troposphere between adjacent air masses with different physical properties.

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

Types :

warm front - an atmospheric front moving towards colder air (heat advection is observed). A warm air mass moves into the region behind a warm front.

On the weather map, a warm front is marked in red or as black semicircles pointing in the direction of the front movement. As the warm front line approaches, pressure begins to drop, clouds thicken, and heavy precipitation falls. In winter, when the front passes, low stratus clouds usually appear. The temperature and humidity of the air are slowly rising. When a front passes, temperature and humidity usually increase rapidly, and the wind increases. After the passage of the front, the direction of the wind changes (the wind turns clockwise), the pressure drop stops and its weak growth begins, the clouds dissipate, and precipitation stops. The baric tendencies field is represented as follows: a closed area of ​​pressure drop is located in front of the warm front, and behind the front there is either an increase in pressure or a relative increase (a drop, but less than in front of the front).

In the case of a warm front, warm air, moving towards a cold front, flows into a wedge of cold air and performs an upward sliding along this wedge and is dynamically cooled. At a certain altitude, determined by the initial state of the rising air, saturation is reached - this is the level of condensation. Above this level, cloud formation occurs in the rising air. The adiabatic cooling of warm air sliding along the cold wedge is enhanced by the development of ascending motions from nonstationarity with a dynamic pressure drop and from wind convergence in the lower layer of the atmosphere. Cooling of warm air during an upward slip over the surface of the front leads to the formation of a characteristic system of stratus clouds (upward slip clouds): cirrus-stratus - high-stratus - nimbostratus (Cs-As-Ns).

When approaching a point of a warm front with well-developed cloudiness, cirrus clouds first appear in the form of parallel bands with claw-like formations in the front (harbingers of a warm front), elongated in the direction of air currents at their level (Ci uncinus). The first cirrus clouds are observed at a distance of many hundreds of kilometers from the front line near the Earth's surface (about 800-900 km). Cirrus clouds then pass into cirrostratus clouds (Cirrostratus). These clouds are characterized by halo phenomena. Clouds upper tier- cirrus-stratified and cirrus (Ci and Cs) consist of ice crystals, and precipitation does not fall out of them. Most often, Ci-Cs clouds are an independent layer, the upper boundary of which coincides with the axis of the jet stream, that is, close to the tropopause.

Then the clouds become denser: altostratus clouds (Altostratus) gradually turn into nimbostratus clouds (Nimbostratus), heavy precipitation begins to fall, which weaken or completely stop after passing the front line. As we approach the front line, the base height Ns decreases. Its minimum value is determined by the height of the level of condensation in the rising warm air. Highly stratified (As) are colloidal and consist of a mixture of tiny droplets and snowflakes. Their vertical power is quite significant: starting at a height of 3-5 km, these clouds extend to heights of the order of 4-6 km, that is, they are 1-3 km thick. The precipitation falling from these clouds in the summer, passing through the warm part of the atmosphere, evaporates and does not always reach the Earth's surface. In winter, precipitation from As in the form of snow almost always reaches the Earth's surface, and also stimulates precipitation from the underlying St-Sc. In this case, the wide precipitation zone can reach a width of 400 km or more. Closest to the Earth's surface (at a height of several hundred meters, and sometimes 100-150 m or even lower) is the lower boundary of nimbostratus clouds (Ns), from which heavy precipitation falls in the form of rain or snow; nimbus clouds often develop under nimbus clouds (St fr).

Clouds Ns extend to heights of 3...7 km, that is, they have a very significant vertical power. The clouds also consist of ice elements and drops, and the drops and crystals, especially in the lower part of the clouds, are larger than in As. The lower base of the As-Ns cloud system in in general terms coincides with the surface of the front. Since the upper boundary of the As-Ns clouds is approximately horizontal, their greatest thickness is observed near the front line. Near the center of the cyclone, where the warm front cloud system has greatest development, the width of the cloudy zone Ns and the zone of extensive precipitation is, on average, about 300 km. In general, As-Ns clouds have a width of 500-600 km, the width of the Ci-Cs cloud zone is about 200-300 km. If projected this system on a surface map, then all of it will be in front of the warm front line at a distance of 700-900 km. IN individual cases The zone of clouds and precipitation can be much wider or narrower, depending on the angle of inclination of the frontal surface, the height of the condensation level, and the thermal conditions of the lower troposphere.

At night, radiation cooling upper bound of the As-Ns cloud system and a decrease in temperature in the clouds, as well as an increase in vertical mixing when the cooled air descends into the cloud, contributes to the formation of an ice phase in the clouds, the growth of cloud elements and the formation of precipitation. As you move away from the center of the cyclone, the ascending air movements weaken, and precipitation stops. Frontal clouds can form not only over inclined surface front, and in some cases - and on both sides of the front. This is especially typical for the initial stage of the cyclone, when ascending movements capture the region behind the front - then precipitation can also fall from both sides of the front. But behind the front line, the frontal cloudiness is usually highly stratified, and behind the frontal precipitation is more often in the form of drizzle or snow grains.

In the case of a very flat front, the cloud system can be shifted forward from the front line. In the warm season, ascending movements near the front line become convective, and cumulonimbus clouds often develop on warm fronts and showers and thunderstorms are observed (both during the day and at night).

In summer, in the daytime, in the surface layer behind the warm front line, with significant cloud cover, the air temperature over land can be lower than ahead of the front. This phenomenon is called warm front masking.

The cloudiness of old warm fronts can also be stratified along the entire length of the front. Gradually, these layers dissipate and precipitation stops. Sometimes a warm front is not accompanied by precipitation (especially in summer). This happens when the moisture content of warm air is low, when the level of condensation lies at a considerable height. When the air is dry, and especially in the case of its noticeable stable stratification, the upward sliding of warm air does not lead to the development of more or less powerful clouds - that is, there are no clouds at all, or a band of clouds of the upper and middle tiers is observed.

cold front - an atmospheric front (a surface separating warm and cold air masses) moving towards warm air. Cold air advances and pushes warm air: cold advection is observed, a cold air mass comes to the region behind the cold front.

On the weather map, a cold front is marked in blue or as black triangles pointing in the direction of the front movement. When crossing the line of a cold 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 southwest, south (in front of the front) to the west, northwest (behind the front). This increases the wind speed. Atmospheric pressure ahead of the front changes slowly. It can fall, but it can also grow. With the passage of a cold front, a rapid increase in pressure begins. Behind the cold front, the pressure increase can reach 3–5 hPa/3 h, and sometimes 6–8 hPa/3 h or even more. A change in the pressure trend (from falling to rising, from slow to stronger growth) indicates the passage of a surface front line.

Before the front, precipitation is often observed, and often thunderstorms and squalls (especially in the warm half of the year). The air temperature after the passage of the front drops (cold advection), and sometimes quickly and sharply - by 5 ... 10 ° C or more in 1-2 hours. The dew point decreases along with the air temperature. Visibility tends to improve as the cold front is invaded by a cleaner and less wet air from northern latitudes.

The nature of the weather on a cold front differs markedly depending on the speed of the front displacement, the properties of warm air in front of the front, and the nature of the ascending motions of warm air above the cold wedge.

There are two types of cold fronts:

cold front of the first kind, when cold air advances slowly,

cold front of the second kind, accompanied by a rapid onset of cold air.

Front of occlusion - an atmospheric front associated with a heat ridge in the lower and middle troposphere, which causes large-scale ascending air movements and the formation of an extended zone of clouds and precipitation. Often, the occlusion front occurs due to closure - the process of displacing warm air upwards in the cyclone due to the fact that the cold front “catches up” with the warm front moving ahead and merges with it (the process of cyclone occlusion). Occlusion fronts are associated with intense precipitation, summer time - heavy showers and thunderstorms.

Due to downward movements in the cold air behind the cyclone, the cold front moves faster than the warm front and overtakes it over time. At the stage of cyclone filling, complex fronts arise - occlusion fronts, which are formed when cold and warm atmospheric fronts meet. In the occlusion front system, three air masses interact, of which the warm one no longer comes into contact with the Earth's surface. Warm air in the form of a funnel gradually rises up, and its place is taken by cold air coming from the sides. The interface that occurs when the cold and warm fronts meet is called the occlusion front surface. Occlusion fronts are associated with intense precipitation, and strong thunderstorms in summer.

Air masses closing during occlusion usually have different temperature- one may be colder than the other. In accordance with this, two types of occlusion fronts are distinguished - occlusion fronts of the warm front type and occlusion fronts of the cold front type.

IN middle lane In Russia and the CIS, warm fronts of occlusion predominate in winter, since temperate sea air enters the rear of the cyclone, which is much warmer than continental temperate air in front of the cyclone. In summer, cold fronts of occlusion are mainly observed here.

The baric field of the occlusion front is represented by a well-defined trough with V-shaped isobars. In front of the front on the synoptic map there is an area of ​​pressure drop associated with the surface of the warm front, behind the front of occlusion there is an area of ​​pressure increase associated with the surface of the cold front. The point on the synoptic map from which the remaining open sections of the warm and cold fronts in the occluding cyclone diverge is the point of occlusion. As the cyclone occludes, the occlusion point shifts to its periphery.

In the anterior part of the occlusion front, cirrus (Ci), cirrostratus (Cs), altostratus (As) clouds are observed, and in the case of active occlusion fronts, nimbostratus (Ns). If a cold front of the first kind is involved in the occlusion, then a part of the cold front cloud system may remain above the upper warm front. If a cold front of the second kind is involved, then a clearing occurs behind the upper warm front, but a shaft of cumulonimbus clouds (Cb) can develop near the lower cold front already in the front cold air, displaced by a colder rear wedge. Thus, precipitation from Altostratus and Doge Stratoclouds (As-Ns), if it occurs, may begin before the occurrence of showers, either simultaneously with or after the passage of a lower cold front; Precipitation can fall on both sides of the lower front, and the transition from heavy precipitation to showers, if it occurs, occurs not ahead of the lower front, but in close proximity to it.

The approaching cloud systems of warm and cold fronts mainly consist of As-Ns. As a result of the approach, a powerful Cs-As-Ns cloud system arises with the greatest thickness at the upper cold front. In the case of a young occlusion front, the cloud system starts with Ci and Cs, which change to As, then to Ns. Sometimes Ns can be followed by Cb, followed again by Ns. A weak upward sliding of the rear air along the occlusion surface can lead to the formation of stratus and stratocumulus (St-Sc) clouds along it, which do not reach the level of ice cores. Of these, drizzling precipitation will fall in front of the lower warm front. In the case of an old warm front of occlusion, the cloud system consists of cirrostratus (Cs) and altocumulus (Ac) clouds, sometimes joined by altostratus (As); rainfall may be absent.

Stationary front

1. A front that does not change its position in space.

2. A front along which air masses move horizontally; front without slips.

32) cyclones and anticyclones. Stages of their development, systems of winds and clouds in them.

Anticyclone- area of ​​increased atmospheric pressure with closed concentric isobars at sea level and with a corresponding wind distribution. In a low anticyclone - cold, isobars remain closed only in the lowest layers of the troposphere (up to 1.5 km), and in the middle troposphere high blood pressure not found at all; the presence of a high-altitude cyclone above such an anticyclone is also possible.

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.

Change weather conditions is due to 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 different 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 by such a collision can reach speeds of 200 km/k at an altitude of 10 km from 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.

Cold front of the 2nd kind in summer period 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 Northern Arctic Ocean, Atlantic and 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.

South part Far East affected by the tropical front. Abundant precipitation in central Russia is caused by the influence of the polar front, which operates in July.

Air masses move around the planet as a whole. Atmospheric fronts, or simply fronts, are transitional zones between two different air masses. Transition zones between adjacent air masses with different properties are called atmospheric fronts. Home feature 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 occurs when masses of cold and warm air approach and meet in the lower layers of the atmosphere or in 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 atmospheric front zone is very narrow compared to the air masses it separates. In the presence of motion, 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 - a few 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 large-scale vertical sections of the atmosphere 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 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 the fronts, as well as air masses, is thousands of kilometers, along the vertical - about 5 km, the width of the frontal zone to the Earth's surface - about a hundred 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 ground level and above.

The fronts between the air masses of the above main geographic types are 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 geographical type are divided into warm, cold and slow-moving (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 meet. Fronts of occlusion can be of the type of both cold and warm fronts. On weather maps, fronts are drawn either as colored lines or as symbols.

Complex complex fronts - occlusion fronts are formed by the merging of cold and warm fronts during the occlusion of cyclones. Distinguish warm front occlusion when the air behind the cold front is warmer than the air ahead of the warm front, and occlusion cold front 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. The main 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 intra-mass precipitation that is not associated with fronts.

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

With height, the temperature contrasts on the axis of the baric trough decrease - the axis of the trough shifts towards lower air temperatures and tends to coincide with the axis of the thermal trough, where temperature contrasts are minimal. So, 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, 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 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 as colored lines or as symbols.

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.

Baric saddles and associated wind deformation fields play a special role in the formation and erosion of various types of atmospheric fronts. 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 atmospheric front surface profile depends on the difference in temperature and wind speed between warm and cold air mass. 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 currents with high speeds and large horizontal extension. 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 system clouds and the more probable precipitation is, a drop in pressure 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. Atmospheric pressure behind its line increases.

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.

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

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

Characteristics of atmospheric fronts

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

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

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

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

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