How does the weather change with a warm front? cold front? Atmospheric fronts Local signs of unstable weather of a cyclonic nature

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 of the upper tier - cirrostratus 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 general 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 system of warm front clouds is most developed, the width of the cloud zone Ns and the zone of overt 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 we project this system onto a surface map, then all of it will be in front of the warm front line at a distance of 700-900 km. In some cases, the zone of cloudiness 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, radiative cooling of the upper boundary of the As-Ns cloud system and a decrease in temperature in the clouds, as well as increased vertical mixing when the cooled air descends into the cloud, contribute 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 above the inclined surface of the front, but in some cases - 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 on 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.

Wikimedia Foundation. 2010 .

• Levi Civita, Tullio
• Bondar, Nikolay Semyonovich

See what "Warm Front" is in other dictionaries:

Front of occlusion- The occlusion front is 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 front of occlusion ... ... Wikipedia

front atmospheric

FRONT ATMOSPHERIC- transition zone (width of several tens of kilometers) between air. masses with different physical. properties. Distinguish between the Arctic front (between arctic and mid-latitude air), polar (between mid-latitude and tropical air) and tropical (between tropical and eq. ... ... Natural science. encyclopedic Dictionary Encyclopedia "Aviation"

atmospheric front- Rice. 1. Scheme of a warm front in a vertical section. atmospheric front - a transition zone between air masses, parts of the lower layer of the Earth's atmosphere (troposphere), the horizontal dimensions of which are commensurate with large parts of the continents and ... ... Encyclopedia "Aviation"

Catafront- Atmospheric front (from other Greek ατμός steam, σφαῖρα ball and lat. frontis forehead, front side), fronts are tropospheric transition zone in the troposphere between adjacent air masses with different physical properties. An atmospheric front occurs when ... ... Wikipedia

Atmospheric fronts- Atmospheric front (from other Greek ατμός steam, σφαῖρα ball and lat. frontis forehead, front side), fronts are tropospheric transition zone in the troposphere between adjacent air masses with different physical properties. An atmospheric front occurs when ... ... Wikipedia

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, it 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 a warm and a cold front 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

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

Air masses and atmospheric fronts

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

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

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

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

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

Warm and cold fronts

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

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

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

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

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

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

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

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

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

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

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

Atmospheric fronts of Russia

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

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

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

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

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

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

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

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

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.

We considered the warm front of the cyclone. Now let's look at the cold front. We will analyze the features and external manifestations that allow yachting to prepare for its approach. Cold areas are called sections of the main front, moving towards a relatively warm air mass. Behind the cold front moving cold air mass. If the air flow is directed from a cold air mass to a warmer one, then such a front is called a cold front. The lagging of the lower layers of air from the upper ones under the influence of friction on the earth's surface leads to the fact that the upper layers collapse down and take the form of a rolling shaft. Displaced straight up warm air quickly rises and forms a ridge of dark clouds - cumulonimbus clouds. Depending on the speed of air movement, cold fronts of the first kind (the speed of movement is low) and the second kind are distinguished.

The structure of the cold front.

The structure of a cold front differs depending on whether it is moving fast or slow. For this reason, there are:
- a cold front of the first kind - a slowly moving one, in which clouds and precipitation are located mainly behind the front line, which makes it difficult for yachting to detect its approach;
- cold front of the second kind - fast moving, in which clouds and precipitation are located mainly in front of the front line.

A cold front of the second kind is observed in the central part of the cyclone, and the first kind - on its periphery.

Cold front of the first kind.

With a cold front of the first kind, masses of warm air are displaced by a wedge of cold air invading under it. Here the cloud character is a mirror image of cloud cover. Immediately ahead of the cold atmospheric front line, cumulonimbus clouds (CL) form, from which showers fall, accompanied by thunderstorms. The width of the zone of shower cloudiness is several tens of kilometers.

The M3-Az cloud system with extensive precipitation is located behind the cold front line. The width of the cloudy zone, its thickness and, accordingly, the width of the precipitation zone are approximately half that of the warm one. Thus, unlike a warm front, the cloudiness system of a cold front of the first kind does not allow yachtsmen to detect its approach in advance by clouds.

Cold front of the second kind.

A cold front of the second kind is distinguished by the fact that the rapid movement of an air shaft causes a rapid rise of the displaced warm air in front of the front line, and downward movements of air currents prevent the cloud system from spreading directly behind the front line. The emerging cloud system is basically a shaft of powerful clouds Cb. When they spread in small quantities, Cc, Ac and Sc can be formed, and below them, in the zone of heavy rainfall, broken cumulus bad weather is usually observed. At altitudes of 4-5 km, the ascending flow of adiabatically cooled moist air meets the descending flow of adiabatically heated dry air. As a result, an upper secondary front is formed, under which the cloud bank Cb is pulled forward. Its leading edge, which has the character of Az, can gradually separate into ridges of lenticular clouds Ac. These clouds are carried forward for 200 - 300 km and their detection is a reliable warning in yachting about the approach of a cold front of the second kind.

Behind the line of the cold atmospheric front, descending air movements are observed in the air mass, especially significant in the front part of the air wedge. Therefore, intramass clouds do not arise here. Soon after the passage of the cold front line, a rapid clearing occurs, up to a complete one; only after a few hours, when the downward motions die out and the frontal surface rises sufficiently, can convective clouds and showers characteristic of an unstable mass appear.

Showers during the passage of a cold front of the second kind are short (from several minutes to 1 hour), since the width of the precipitation zone is small, and the movement speed is significant. In the shaft of cumulonimbus clouds, breaks or less developed cloudiness of the lower and middle tiers are sometimes found. Thunderstorm activity develops in some areas, which, having faded in some areas, may appear in neighboring ones.

The direction of the wind during the passage of cold fronts of both kinds changes in the same way as in the case of a warm one, but the turn to the right (in the northern hemisphere) at the moment of passage is more significant and sharp. At the same time, the wind speed increases sharply.
When a cold front approaches, there is a short, usually weak, but gradually accelerating pressure drop. Immediately after the passage, the pressure rises due to the replacement of warm air by cold air.

The air temperature after passing the cold front line decreases. The temperature jump depends on the nature of the changing masses.

Cold fronts of both types are characterized by pre-frontal squalls, which are especially dangerous phenomena for yachting. The air behind the cold front is characterized by downward movement, which becomes especially intense in the front of the wedge, where friction creates a steep slope of the front surface. The air, falling down, seems to roll forward, like the caterpillars of a tank, and the speed of its advance in all cases turns out to be greater than the corresponding component of the speed of warm air in the lower layers. Collapse of cold air leads to upward displacement of warm air and to the appearance of a vortex with a horizontal axis; the phenomena of frontal squalls are connected with this vortex.

Especially intense downward movement takes place in the head of cold air. Descending from a height of several kilometers, this air heats up adiabatically, and due to this, the temperature jump is smoothed out. In some cases, a secondary cold front arises inside the cold wedge, separating the heated air of the "head" from the air lying further and not captured to such an extent by the downward movement.

This second cold front goes several kilometers behind the eroded main one. During its passage, there is a jump in temperature, winds and squalls, but it does not have a cloud system. This phenomenon is called the bifurcation of the cold front. Yachtsmen must always keep this in mind and not relax after the passage of a cold front. Squalls without a visible cloud system can cause a lot of problems in yachting. As they say, he crept up unnoticed.

In baric troughs in the rear of the cyclone, secondary cold fronts usually form. They have a cloud system similar to that of a cold front of the second kind, however, the vertical extent of the clouds in them is less than the extent of the clouds of the main fronts. In some cases, there may be several troughs and secondary fronts.

Sedentary (stationary) are sections of the main front that do not undergo significant movement.
In a cyclone, a cold front moves somewhat faster than a warm one. Over time, they converge, and then merge, starting near the center of the cyclone. Such a front, formed as a result of the merger of cold and warm, is called an occlusion front (closed). But about this in.