Where the warm atmospheric front comes from. Warm front, its features, clouds. Influence on the weather

Atmospheric frontshave several different characteristics. According to them there is a division of this natural phenomenon on different types.

Atmospheric fronts can be 500-700 km wide and 3000-5000 km long.

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

Characterization of atmospheric fronts

By displacement, atmospheric fronts can be divided into cold, warm, and occlusion fronts.
Warm atmospheric is formed when warm air masses, as a rule, humid ones, approach 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, which inject cold air into areas that were previously occupied by a warm front. The cold atmospheric front affects the weather in a small strip 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, considered the most powerful and destructive in history, hit the Ganges delta in eastern Pakistan in November 1970. The wind speed reached over 230 km / h, and the tidal wave height was about 15 meters.

Occlusion fronts arise when one atmospheric front is superimposed 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 displaced and separated from the earth's surface. As a result, the front will mix at the surface of the earth under the influence of two cold air masses. Deep wave cyclones formed in the form of very chaotic wave disturbances are often located at the occlusion fronts. At the same time, the wind increases significantly, and the wave becomes clearly pronounced. As a result, the front of the occlusion turns into a large blurred frontal zone and after some time completely disappears.

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

On a warm front, warm air flows into cold air located in the form of a wedge at the bottom. Ahead of the surface line, there is an area of \u200b\u200bpressure drop, which is due to the replacement of cold air with warm air. With a decrease in pressure, the wind increases, reaches its maximum speed before passing the front, then weakens. Ahead of the front, southeasterly winds prevail, passing behind the front to southern and southwestern.

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

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

The main cloud system of the front is the Ns-As stratus and high-stratus clouds located in the lower and middle tiers (5-6 km). Their upper border is almost horizontal, and the lower one goes down 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 upper tier clouds are separated from the Ns-As system by a cloud layer. A zone of overburden precipitation is observed under the main cloud system. It lies in front of the surface front line and has a normal length from the front up to 400 km.

In the precipitation zone, low torn-rain clouds form with a lower boundary of 50-100m, sometimes frontal fogs appear, at temperatures from 0 to –3 ice is observed.

In winter, with strong winds, the passage of the front is accompanied by strong snowstorms. In summer, separate centers of cumulonimbus clouds with showers and thunderstorms may 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 cloud layers. 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 stratus clouds, which makes them difficult to visualize. When approaching stratus clouds, inside which cumulonimbus are hidden, turbulence (turbulence) begins, increased electrification, which negatively affects the operation of instrumental equipment.

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

The warm front is marked in red or blackened semicircles directed towards the front movement. As the line of the warm front approaches, the pressure begins to drop, clouds thicken, and heavy precipitation falls. In winter, low stratus clouds usually appear when the front passes. Temperature and humidity rise slowly. When the front passes, temperature and humidity usually rise rapidly, and the wind increases. After the front has passed, the wind direction changes (the wind turns clockwise), the pressure drop stops and its weak growth begins, the clouds dissipate, and precipitation stops. The field of baric tendencies is presented as follows: a closed region of pressure drop is located in front of the warm front, behind the front there is either an increase in pressure or a relative increase (a drop, but less than before the front).

In the case of a warm front, warm air, moving towards the cold one, flows onto a wedge of cold air and makes an upward slide along this wedge and is dynamically cooled. Saturation is reached at a certain altitude, determined by the initial state of the rising air - 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 upward motions from unsteadiness with a dynamic pressure drop and from the convergence of the wind in the lower atmosphere. Cooling of warm air during an ascending glide along the surface of the front leads to the formation of a characteristic system of stratus clouds (clouds of ascending sliding): cirrostratus - high-stratus-nimbostratus (Cs-As-Ns).

When approaching the point of a warm front with well-developed cloudiness, cirrus clouds first appear in the form of parallel stripes with claw-like formations in the front part (precursors 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 at the Earth's surface (about 800-900 km). Cirrus clouds then pass into cirrostratus (Cirrostratus). These clouds are characterized by halo phenomena. The upper tier clouds, cirrostratus and cirrus (Ci and Cs), are composed of ice crystals, and no precipitation falls 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, it is close to the tropopause.

Then the clouds become denser: altostratus clouds (Altostratus) gradually turn into nimbostratus (Nimbostratus), heavy precipitation begins to fall, which weaken or completely stop after passing the front line. As the front line is approached, the base height Ns decreases. Its minimum value is determined by the height of the condensation level in the rising warm air. Highly layered (As) are colloidal and consist of a mixture of tiny droplets and snowflakes. Their vertical thickness is quite significant: starting at an altitude 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 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 underlying St-Sc. In this case, the width of the overburden zone can reach a width of 400 km or more. Closest to the Earth's surface (at an altitude of several hundred meters, and sometimes 100-150 m and even lower) is the lower boundary of stratus clouds (Ns), from which heavy precipitation falls in the form of rain or snow; under nimbostratus clouds, torn rains (St fr) often develop.

Ns clouds extend to heights of 3… 7 km, that is, they have a very significant vertical thickness. Clouds are also composed of icy elements and droplets, and the droplets 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 front surface. Since the tops of As-Ns clouds are approximately horizontal, their greatest thickness is observed near the front line. Near the center of the cyclone, where the cloud system of the warm front has the greatest development, the width of the cloud zone Ns and the zone of overlying precipitation is on average about 300 km. In general, As-Ns clouds are 500-600 km wide, and the Ci-Cs cloud zone is about 200-300 km wide. If you 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 cloudiness and precipitation zone 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 of the upper boundary 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 clouds, the growth of cloud elements, and precipitation. As the distance from the cyclone center increases, the ascending air movements weaken, 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 the ascending movements capture the frontal area - then precipitation can fall on both sides of the front. But behind the front line, the frontal cloudiness is usually strongly stratified, and the frontal precipitation is more often presented as drizzle or snow grains.

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

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

The clouds 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 with a low moisture content of warm air, when the level of condensation is at a considerable height. With dry air 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 there is a band of upper and middle tiers of clouds.

Wikimedia Foundation. 2010.

See what "Warm Front" is in other dictionaries:

The occlusion front is an atmospheric front associated with a heat crest 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

Transition zone (width of several tens of kilometers) between air. masses with different physical. properties. Distinguish arctic. front (between arctic and mid-latitude air), polar (between mid-latitude and tropical air) and tropical (between tropical and eq. ... ... Natural science. encyclopedic DictionaryEncyclopedia "Aviation"

atmospheric front - Fig. 1. Diagram of a warm front in a vertical section. an atmospheric front is a transitional 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"

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

Ns clouds extend to heights of 3 ... 7 km, that is, they have a very significant vertical thickness. Clouds are also composed of icy elements and droplets, and the droplets and crystals, especially in the lower part of the clouds, are larger than in As. The bottom base of the As-Ns cloud system roughly coincides with the front surface. Since the tops of As-Ns clouds are approximately horizontal, their greatest thickness is observed near the front line. Near the center of the cyclone, where the cloud system of the warm front has the greatest development, the width of the cloud zone Ns and the zone of overlying precipitation is on average about 300 km. In general, As-Ns clouds are 500-600 km wide, and the Ci-Cs cloud zone is about 200-300 km wide. If you 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 cloudiness and precipitation zone 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.

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 crest 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 arctic. front (between arctic and mid-latitude air), polar (between mid-latitude and tropical air) and tropical (between tropical and eq. ... ... Natural science. encyclopedic DictionaryEncyclopedia "Aviation"

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

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

In the previous article, we examined the reasons for the appearance of wind, which are cyclones and anticyclones and their interaction. Of course, a yachtsman is primarily interested in cyclones that bring bad weather with strong winds that 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 carries with it atmospheric fronts - warm and cold, each of which has certain properties, and which we will study in this article.
The 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 the fronts causes changes in pressure, direction and strength of wind, humidity, and cloudiness. There are several types of atmospheric fronts: warm front, cold front, occlusion 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 consider the structure of a cyclone with fronts as a whole.

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

Figure: G450a Typical cyclone with edges

The following illustration of G450b shows the distribution of cloudiness at the fronts.

Figure: G450b

The precipitation and when passing the fronts is shown in Figure G450c

Figure: G450c

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

Front	Warm	Cold	Front of occlusion	Stationary
Weather	Continuous rain, then fog	Heavy rain, showers	Rain, then squalls	Periodic rain then clearing
Major clouds	Layered	Cumulonimbus	Layered, then rain	Low-layered, then rainy
Temperature change	Growing slowly	Drops when passing the front	Rises or falls	Growing slowly
Wind speed	10-15 knots	15 -30 knots	10-15 knots	Quiet or calm
Front designation on meteo maps

Table 1.

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

Warm front

Any front (other than occluded) that moves in such a way that cold air is replaced by warm air when the front passes, is called a warm front. (See figure G207a)

Figure: G207a

The warm front comes in as follows. After the first appearance of cirrus clouds, the sky gradually decreases, filling with cirrostratus clouds. A 22-degree halo around the sun or moon informs us of the presence of ice crystals in these clouds, which we might not have noticed if it weren't for this halo. A continuous, light rain begins somewhere in the middle between the first appearance of cirrus clouds and the passage of the front itself. The pressure gradually decreases, and the wind increases as it passes the front, reaches the greatest force and turns sharply clockwise. See table 2 for details on warm front characteristics.

	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 layered rain	Stratus or stratocumulus
Wind	Constantly amplifies and turns counterclockwise	Turns sharply clockwise	Constant direction and strength
Pressure	Falls constantly	Smallest value	Minor changes
Temperature	Stable or slightly growing	Rising	Doesn't change or grows slightly
Visibility		Bad because of the fog	Good or bad in fog or drizzle

Table 2. Warm front

Cold front

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

Figure: G207b

When approaching, the cold front looks like a wall of dark cumulonimbus thunderclouds... When passing the front, pouring rain with a thunderstorm is expected, 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 thunderstorm	Heavy rain with a thunderstorm. 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	Is getting stronger and getting squally	Turns sharply clockwise, very squishy	Gusty, changes direction clockwise
Pressure		Rises sharply	Rising slowly
Temperature	May fall a little	Falls sharply	Slowly falls a little
Visibility		Decreases sharply	Mostly good

Table 3. Cold front

Warm sector
The area of \u200b\u200bwarm air in a cyclone bounded by a warm and cold front is called a warm sector. It is characterized by more or less straight isobars. (See Figure G207e)

Figure: G207e

The weather in the warm sector is characterized by strong winds of constant strength and direction. 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 occlusion front. This is a common process in the last stage of cyclone development, when a cold front catches up with 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 Figure G207c)

Figure: G207c. Different types of occluded fronts

Weather conditions during the passage of such fronts are also unfavorable for yachtsmen - they are accompanied by rains with thunderstorms and hail, strong and gusty winds with a sharp change in directions and, at times, poor visibility.

Stationary front
A front that is motionless or nearly motionless is called a stationary front. Typically fronts moving at a speed of less than 5 knots are considered stationary. (See Figure G207d)

Figure: 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 front can stop in their motion and turn into a stationary front. In this case, it has the weather of the front from which it formed. At some stage in its existence, the stationary front will have the weather conditions of the occlusion 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 in an east and northeast direction, and their fronts are in the southern part of the cyclone. If a yachtsman happens to be in this part of the cyclone, he is on the “dangerous side” of the cyclone and must be prepared to face very difficult 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 the cyclone and the fronts over the observer, who is on the dangerous side of the cyclone. The mechanism of this phenomenon is discussed in detail in the article “In a storm. Areas of a cyclonic storm dangerous for navigation ”.
Figure G136a shows the change in pressure along the path of a yacht through the cyclone fronts.

Figure: G136a

As a warm front approaches, atmosphere 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 usually decreases constantly or slightly so that when the cold front passes, its growth begins.

Figure G136b shows the change in wind force measured on board the yacht as it passes through the fronts:

Figure: G136b

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

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

Figure: G136c

The wind slowly turns counterclockwise as a warm front approaches. Directly at the front, it sharply changes direction clockwise, in accordance with the sharp bend of the isobars. This change in direction occurs on all fronts. In a warm sector, the wind direction is stable. On a cold front, the change in wind direction can be greater than on a warm one. Then the wind goes smoothly clockwise 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 probability what conditions we may encounter in a cyclone with fronts.

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

Visit and review the article

Where the warm atmospheric front comes from. Warm front, its features, clouds. Influence on the weather

Characterization of atmospheric fronts

See what "Warm Front" is in other dictionaries:

See what "Warm Front" is in other dictionaries:

The last

You need to know