Numerology 

Meteorological dictionary - a glossary of meteorological terms. How does the weather change with a warm front? cold front? Signs of a possible overnight thunderstorm

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 ​​of 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. After a few hours, cirrus clouds, condensing, pass into a veil of cirrostratus 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 occur in the inner parts of 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. In the warm season, in the front part of such a front, favorable conditions are created for the formation of powerful cumulonimbus clouds (Cb), from which heavy precipitation falls, 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 the cold air mass behind the cold front is warmer than the cold mass ahead of the front, then it, while displacing the 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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At the warm front, warm air flows into the cold, located in the form of a wedge at the bottom. Ahead of the surface line, there is an area of ​​pressure drop, which is due to the replacement of cold air with warm air. As the pressure drops, the wind increases, reaches its maximum speed before the passage of the front, then weakens. Winds of the southeast direction predominate ahead of the front, passing behind the front to the south and southwest.

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

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

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

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

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

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

In the previous article, we considered the causes of the appearance of wind, which are cyclones and anticyclones, and their interaction. Of course, the yachtsman is primarily interested in cyclones that bring bad weather with strong winds, which he would like to avoid, or at least know what conditions he will have to face in order to prepare for them. Usually, a cyclone brings with it atmospheric fronts - warm and cold, each of which has certain properties, and which we will study in this article.
An atmospheric front is the interface between two air masses of different densities. Since temperature is the main regulator of air density, the front usually separates air masses with different temperatures. Along with these characteristics, the passage of fronts causes a change in pressure, direction and strength of wind, humidity, and cloudiness. There are several types of atmospheric fronts: warm front, cold front, occlusive front, and stationary front. Usually, the front is named according to the temperature of the air mass following it. The front, behind which there is warm air (or the warm sector of the cyclone), is called a warm front, and vice versa, if cold air comes behind the front, this is a cold front. Before considering the features of each of them, let's look at the structure of a cyclone with fronts in general.

Figure G450a shows a cyclone with fronts and wind directions in it.

Rice. G450a Typical cyclone with fronts

The following illustration of G450b shows the distribution of cloud cover on the fronts.

Rice. G450b

Precipitation and fronts are shown in figure G450c

Rice. G450c

The above figures clearly demonstrate what different conditions we face when passing fronts. Comparative characteristics of the fronts are given in Table 1.

Front

Warm

Cold

Front of occlusion

Stationary

Weather

Continuous rain, then fog

pouring rain, downpours

Rain, then squalls

Intermittent rain, then clearing

Main clouds

layered

Cumulonimbus

Layered, then rain

Low-stratified, then rainy

Temperature change

growing slowly

Falls sharply when passing the front

Rising or falling

growing slowly

Wind speed

10 -15 knots

15 -30 knots

10 -15 knots

Quiet or calm

Front designation on weather maps

Table 1.

Let's take a closer look at each of the atmospheric fronts.

warm front

Any front (other than an occluded one) moving in such a way that cold air is replaced by warm air as the front passes is called a warm front. (See Fig. G207a)

Rice. G207a

The warm front comes as follows. After the first appearance of cirrus clouds, the sky gradually lowers, filling with cirrostratus clouds. A 22-degree halo around the sun or moon informs us about the presence of ice crystals in these clouds, which we might not have noticed without this halo. Continuous, fine rain begins somewhere in the middle of the path between the first appearance of cirrus clouds and the passage of the front itself. The pressure gradually drops, and the wind intensifies, and when the front passes, it reaches its greatest strength and turns sharply clockwise. Read more about the characteristics of the warm front in Table 2.

Before the front

When passing the front

Behind the front

Weather

Continuous rain or snow

The rain is ending

Drizzle or light rain

Cloudiness

Sequentially Ci, Cs, As, Ns

Low nimbostratus

Stratocumulus or Stratocumulus

Wind

Constantly amplifies and turns counterclockwise

Turns sharply clockwise

Constant direction and strength

Pressure

Constantly falling

Lowest value

Slight changes

Temperature

stable or growing slightly

rises

Does not change or slightly increases

Visibility

Bad because of the fog

Good or bad in fog or drizzle

Table 2. Warm front

cold front

Any front (other than an occluded one) moving in such a way that warm air is replaced by cold air as it passes is called a warm front. (See Fig. G207b)

Rice. G207b

As it approaches, a cold front looks like a wall of dark cumulonimbus thunderclouds. During the passage of the front, heavy rain is expected with a thunderstorm, possibly hail. The wind is gusty and abruptly changes direction clockwise. Then the sky clears up.
See Table 3 for details.

Before the front

When passing the front

Behind the front

Weather

Chance of rain or thunderstorms

Torrential rain with thunder. Possibly hail

Downpour turning into light rain and clearing

Cloudiness

Ac, As and Ns followed by cumulonimbus

Thunderstorm cumulonimbus

Rapidly rising As, Ac, clearing

Wind

Strengthens and becomes squally

Turns sharply clockwise, very squally

Choppy, changes direction clockwise

Pressure

rises sharply

rising slowly

Temperature

Might fall a little

Falls sharply

Slowly falling a little

Visibility

Decreases sharply

Mostly good

Table 3. Cold front

Warm sector
The area of ​​warm air in a cyclone, bounded by a warm and cold front, is called the warm sector. It is characterized by more or less straight isobars. (See Fig. G207e)


Rice. G207e

Weather in the warm sector is characterized by strong winds of constant force and direction. There are cumulus and stratocumulus clouds in the sky, showers periodically.

Front of occlusion
A front consisting of two fronts and formed in such a way that a cold front overlaps a warm or stationary front is called an occluded front. This is a common process in the last stage of cyclone development, when a cold front overtakes a warm one. There are three main types of occlusion fronts due to the relative coolness of the air mass following the initial cold front towards the air ahead of the warm front. These are fronts of cold, warm and neutral occlusion. (See fig. G207c)


Rice. G207c. Occluded fronts of different types

The weather conditions during the passage of such fronts are also unfavorable for yachtsmen - they are accompanied by rain with thunderstorms and hail, strong and gusty winds with a sharp change in direction and sometimes poor visibility.

Stationary front
A front that is stationary or nearly stationary is called a stationary front. Usually, fronts moving at a speed of less than 5 knots are considered to be stationary. (See fig. G207d)

Rice. G207d. Stationary front

The weather conditions of a stationary front cannot be described as belonging to this particular front, for the reason that both warm and cold fronts can stop in their movement and turn into a stationary front. In this case, it has the weather of the front from which it formed. At some stage of existence, a stationary front will have the weather conditions of an occluded front. Once it remains stationary for a long period of time, there is a high probability of acquiring the properties of a warm front.

In the middle latitudes of the northern hemisphere, cyclones usually move eastward and northeastward, and their fronts are in the southern part of the cyclone. If a boater happens to be in this part of the cyclone, he is on the "danger side" of the cyclone and should be prepared to face some very severe weather conditions. The left side of the cyclone is safer for navigation. Even cyclones without fronts have significantly stronger winds on their dangerous side. Therefore, it will be interesting to consider the passage of a cyclone and fronts over an observer located on the dangerous side of the cyclone. The mechanism of this phenomenon is considered in detail by us in the article “In the storm. Areas of a cyclonic storm dangerous for navigation.
Figure G136a shows the change in pressure along the path of the yacht passing through the fronts of the cyclone.

Rice. G136a

As a warm front approaches, atmospheric pressure decreases and stabilizes behind the front, in the warm sector. There is usually a sharp bend in the isobars at the front lines, reflecting the difference in the structure of the air masses. When a cold front approaches, the pressure is usually constantly or slightly reduced so that when the cold front passes, it begins to increase.

Figure G136b shows the change in wind strength measured aboard the yacht as it passes through fronts:

Rice. G136b

The wind speed gradually increases with the approach of a warm front and then stabilizes in the warm sector. After the passage of the cold front, the wind strength decreases. It reaches its greatest strength during the passage of fronts. In both cases, when crossing fronts, the wind becomes gusty and squally.

The change in wind direction when the yacht crosses the fronts is shown in Figure G136c:

Rice. G136s

The wind slowly turns counterclockwise as a warm front approaches. Directly at the front, it abruptly changes direction clockwise, in accordance with the sharp bend in the isobars. This change of direction is happening on all fronts. In the warm sector, the wind direction is stable. On a cold front, the change in wind direction can be greater than on a warm front. The wind then moves smoothly in a clockwise direction at the tail of the cyclone.

Now, armed with knowledge of the nature of cyclones and fronts, we can predict with a high degree of certainty what conditions we might encounter in a cyclone with fronts.

From “Weather trainer” by David Burch
Translation: S.Svistula

Visit and review the article

1. Choose the correct answers. The territory of Russia is dominated by: a) arctic air masses; b) air of temperate latitudes; c) equatorial air masses.

2. Define a weather front. What are atmospheric fronts?

An atmospheric front is a transitional zone in the troposphere between adjacent air masses with different physical properties (primarily temperature). Fronts can be: warm, cold and occlusive (mixed).

3. Choose the correct answers. A warm atmospheric front brings: a) showers, thunderstorms; b) prolonged rains; c) temporary warming; d) rapid cooling; d) clear weather.

Answer: B, C.

4. What is a cyclone? What is an anticyclone? What do they have in common?

A cyclone is an atmospheric vortex of huge (hundreds to several thousand kilometers) diameter with reduced air pressure in the center. Weather in the cyclone: ​​temperature change (warming in winter, cooling in summer), increase in humidity, precipitation, low pressure, cloudy weather, increased wind. An anticyclone is an area of ​​high atmospheric pressure in the center and low pressure at the periphery. Weather in the anticyclone: ​​weak wind, clear and dry weather, temperature change (cold in winter, warm in summer). Cyclones and anticyclones are large atmospheric eddies that carry air masses. On maps, they are distinguished by closed concentric isobars (lines of equal pressure).

5. Match. 1. Cyclone. A. Large atmospheric vortex with high pressure in the center. 2. Anticyclone. B. Cloudy weather. B. Cloudy, warm weather in summer, frosty in winter. D. Large atmospheric vortex with low pressure in the center.

Answer: 1 - A, B; 2 - B, D.

6. Which weather - cyclonic or anticyclonic - leads to more air pollution? Why?

Atmospheric air pollution will be greater during the anticyclone, because. it is dominated by high atmospheric pressure, in which the air has a downward movement. Thus, emissions from pollution sources will go down and form smog, while in a cyclone a strong wind and ascending air currents will lift up and carry away emissions from enterprises.

7. What kind of weather - cyclonic or anticyclonal - was established over the territory of your settlement in this period? Why do you think so?

Anticyclonic weather has now set in, this is evidenced by a sharp drop in temperature (November 14) to -5, the absence of wind and clear, cloudless weather.

8. Observe how the weather sets in your area with the passage of warm and cold fronts. How often does the weather change? What is it connected with?

The weather in the region changes frequently, especially during the warm period of time. This is due to the constant passage of atmospheric fronts that arise due to the geographical location of the region; The Southern Urals is located in the zone of influence of the western Atlantic cyclones, which can reach the Ural Mountains, the northern Arctic air masses and the eastern Siberian anticyclones. When a warm front passes, cirrus clouds form. Gradually, they turn into a continuous white veil - into cirrostratus clouds. Warm air is already moving in the upper atmosphere. The pressure drops. The closer the atmospheric front line is to us, the denser the clouds become. The sun shines through with a dim spot. Then the clouds become lower, the sun disappears completely. The wind intensifies and changes its direction clockwise (for example, at first it was east, then southeast and even southwest). Approximately 300-400 km before the front, the clouds thicken. Light rain or snow begins. When the warm front has passed, the rain or snow has stopped, the clouds disperse, warming sets in - a warmer air mass has arrived. When a cold front passes, warm air recedes and cold air dissipates behind it. His arrival always causes a cold snap. But when moving, not all layers of air have the same speed. The lowest layer, as a result of friction on the earth's surface, is slightly delayed, and the higher layers are pulled forward. Thus, cold air collapses on warm air in the form of a shaft. Warm air is quickly forced upward, and powerful piles of cumulus and cumulonimbus clouds are created. Cold front clouds carry showers, thunderstorms, accompanied by strong gusty winds. They can reach very high altitudes, but in the horizontal direction they extend only 20-30 km. And since the cold front usually moves quickly, stormy weather does not last long - from 15-20 minutes to 2-3 hours. As a result of the interaction of cold air with a warm underlying surface, separate cumulus clouds with gaps are formed. Then comes the clarification.

Watching the weather changes is very exciting. The sun gives way to rain, the rain to snow, and gusty winds blow over all this diversity. In childhood, this causes admiration and surprise, in older people - a desire to understand the mechanism of the process. Let's try to understand what shapes the weather and how atmospheric fronts are related to it.

air mass boundary

In the usual perception, "front" is a military term. This is the edge on which the clash of enemy forces takes place. And the concept of atmospheric fronts is the boundaries of contact between two air masses that form over huge areas of the Earth's surface.

By the will of nature, man was given the opportunity to live, evolve and populate ever larger territories. The troposphere - the lower part of the Earth's atmosphere - provides us with oxygen and is in constant motion. All of it consists of separate air masses, united by a common occurrence and similar indicators. Among the main indicators of these masses determine the volume, temperature, pressure and humidity. During the movement, different masses can approach and collide. However, they never lose their boundaries and do not mix with each other. - these are areas where sharp weather jumps come into contact and occur.

A bit of history

The concepts of "atmospheric front" and "frontal surface" did not arise by themselves. They were introduced into meteorology by the Norwegian scientist J. Bjerknes. It happened in 1918. Bjerknes proved that atmospheric fronts are the main links in the high and middle layers. However, before the research of the Norwegian, back in 1863, Admiral Fitzroy suggested that violent atmospheric processes begin at the meeting places of air masses coming from different parts of the world. But at that moment, the scientific community did not pay attention to these observations.

The Bergen school, of which Bjerknes was a representative, not only carried out its own observations, but also brought together all the knowledge and assumptions expressed by earlier observers and scientists, and presented them in the form of a consistent scientific system.

By definition, the inclined surface, which is the transition area between different air flows, is called the frontal surface. But atmospheric fronts are a display of frontal surfaces on a meteorological map. Usually, the transition region of the atmospheric front is tied up near the surface of the Earth and rises up to those heights at which the differences between air masses are blurred. Most often, the threshold of this height is from 9 to 12 km.

warm front

Atmospheric fronts are different. They depend on the direction of movement of warm and cold massifs. There are three types of fronts: cold, warm and occlusion, formed at the junction of different fronts. Let us consider in more detail what warm and cold atmospheric fronts are.

A warm front is a movement of air masses in which cold air gives way to warm air. That is, the air of a higher temperature, moving forward, is located in the territory where cold air masses dominated. In addition, it rises up along the transition zone. At the same time, the air temperature gradually decreases, due to which condensation of the water vapor in it occurs. This is how clouds form.

The main signs by which you can identify a warm atmospheric front:

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

It usually warms up after the precipitation stops, but this does not last long, because the cold front moves very quickly and catches up with the warm atmospheric front.

cold front

Such a feature is observed: a warm front is always inclined in the direction of movement, and a cold front is always inclined in the opposite direction. When fronts move, cold air wedges into warm air, pushing it up. Cold atmospheric fronts lead to a decrease in temperature and cooling over a large area. As the rising warm air masses cool, the moisture condenses into clouds.

The main signs by which a cold front can be identified are:

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

Traveling through a cold front is no easy task for travelers. Sometimes you have to overcome whirlwinds and squalls in conditions of poor visibility.

Front of occlusions

It has already been said that atmospheric fronts are different, if everything is more or less clear with warm and cold fronts, then the front of occlusions raises a lot of questions. The formation of such effects occurs at the junction of cold and warm fronts. The warmer air is forced upward. The main action occurs in cyclones at the moment when a more rapid cold front catches up with a warm one. As a result, there is a movement of atmospheric fronts and a collision of three air masses, two cold and one warm.

The main features by which you can determine the front of occlusions:

  • clouds and precipitation of a general type;
  • abrupt shifts without a strong change in speed;
  • smooth pressure change;
  • no sudden temperature changes;
  • cyclones.

The occlusion front depends on the temperature of the cold air masses in front of it and behind it. Distinguish between cold and warm occlusion fronts. The most difficult conditions are observed at the moment of direct closure of the fronts. As the warm air is displaced, the front is eroded and improved.

Cyclone and anticyclone

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

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

An anticyclone is an area of ​​high pressure that pushes excess air into areas of low pressure. The main characteristic is clear weather, since clouds are also forced out of this zone.

Geographic division of atmospheric fronts

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

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

Influence of the underlying surface

The physical properties of air masses are affected by radiation and the appearance of the Earth. Since the nature of such a surface can be different, the friction against it occurs unevenly. Difficult geographic topography can deform the atmospheric front line and change its effects. For example, there are known cases of destruction of atmospheric fronts when crossing mountain ranges.

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