The reason for the formation of stratus clouds. How are clouds formed? Types of clouds with descriptions and photos

Clouds are a collection of water droplets and ice crystals suspended in the atmosphere, located at a certain height above the earth's surface. Clouds form as a result of an increase in total moisture content, a decrease in air temperature, or condensation of water vapor below the dew point. The following factors lead to a decrease in air temperature and cloud formation in the atmosphere:

- rise (ascending movements) of air and advection;

- radiation and turbulent mixing (vertical and horizontal).

But this is not enough, there must be condensation (or sublimation) nuclei in the air, on which water or ice begins to precipitate. Condensation nuclei in marine areas can be salt particles that have entered the air along with water dust and spray during storms; on land, these are microscopic particles of dust and smoke.

Clouds are carried by air currents. If a relative humidity decreases in air containing clouds, then the clouds evaporate. Under certain conditions, part of the cloud elements becomes larger and heavier so that it falls out of the cloud in the form of precipitation.

Individual clouds exist a short time. For example, the lifetime of a single cumulus cloud is sometimes calculated as only 10-15 minutes. But even the long existence of a cloud does not mean that it is in an unchanged state. In reality, cloud elements are constantly evaporating and re-emerging. For a long time there is a certain process of cloud formation; the cloud is only visible in this moment part of the total mass of water involved in this process. The appearance of the clouds is also deceptive. If the cloud does not change its height, then this does not mean that its constituent elements do not fall out. Droplets in a cloud may descend, but when they reach the lower boundary of the cloud, they pass into unsaturated air and evaporate.

According to the phase state of cloud elements, clouds are divided into three classes:

· Water (drop) clouds consisting only of water droplets. They can exist not only at positive air temperatures, but also at negative ones (-10°C and below). In this case, the droplets are in a supercooled state.

· mixed clouds, consisting of a mixture of supercooled water droplets and ice crystals. They can exist, as a rule, at air temperatures from -10 to -40°C.

· Ice (crystalline) clouds consisting only of ice crystals. They prevail, as a rule, at air temperatures below -30°C.

The forms of clouds in the troposphere are very diverse. In the modern version international classification clouds are divided into ten basic shapes according to appearance: Cirrocumulus, Cirrostratus, Altocumulus, Altostratus, Stratocumulus, Stratostratus, Stratocumulus, Cumulus, Cumulonimbus.

In addition, clouds are classified by height:

· Upper clouds- the highest clouds of the troposphere, are formed at a height of over 6 kilometers, with the most low temperatures and are made of ice crystals. These clouds are white, translucent and have little shading. sunlight. These include: cirrus, cirrocumulus, cirrostratus clouds.

· Middle clouds- altocumulus and altostratus clouds, formed at an altitude of 2-6 kilometers. High Cumulus clouds are cloud layers or ridges of white or gray color, consist of supercooled droplets. Fairly thin clouds, more or less obscuring the sun. Altostratus clouds - light, milky-gray cloud cover of varying density, covering the sky in whole or in part.

· Clouds lower tier - stratocumulus (ridges or layers of gray or whitish clouds), stratus (uniform gray layer) and nimbostratus clouds, formed at an altitude below 2 kilometers. These clouds consist of small homogeneous droplets. At sufficiently low negative temperatures, solid elements (ice crystals, snow grains, etc.) appear in the clouds. The solar disk, translucent through the stratus clouds, has a clear outline.

· Clouds of vertical development- cumulus and cumulonimbus, are formed when warm air slowly rises above the ground. Cumulus clouds - dense, with sharply defined contours, individual clouds that develop upward in the form of hills, domes and towers. They consist of water droplets (no crystals). Cumulonimbus are formed as a result of the further development of cumulus clouds. These are powerful cumulus-shaped masses, very strongly developed vertically in the form of mountains and towers. Cumulonimbus clouds consist in the upper part of ice crystals, in the middle - of crystals and drops of various sizes, up to large ones. Blocking the sun, they greatly reduce the illumination.

Cumulus clouds (lat. Cumulus) - separately located, dense, with sharp outlines of clouds, developing vertically, and having white cumulus or dome-shaped tops and flat darker (bluish or grayish) bases. With strong gusts of wind, the edges of the clouds are often torn.

Cumulus clouds form in the lower and partly in the middle troposphere during the development of convection in chilled air masses, as well as in warm time years in air masses over warmed land. The height of the lower boundary line of cumulus clouds is strongly influenced by the humidity of the surface air, in moist air masses the height is from 800 to 1.5 km, and in dry air masses (deserts and steppes) - from 2000 to 4000 m. The vertical extent of clouds varies from hundreds meters to thousands of meters. Cumulus clouds are located in the sky as separate sparse clouds, and significant clusters, covering almost the entire sky. Scattered cumulus clouds are randomly scattered across the sky, but can form chains or ridges, while their bases are located on the same level. Cumulus clouds consist of water droplets throughout their thickness, which are larger at the top of the cloud and smaller at the base. At temperatures below zero degrees, the drops are in a supercooled state. The central part of cumulus clouds completely covers the sun, and the edges are still translucent. Precipitation usually does not fall. AT temperate latitudes individual large drops of rain may sometimes fall, sometimes there may be short-term rare rain.

Types of cumulus clouds

Cumulus clouds are divided into four types:

1. Flat (as if flattened) - the most variable clouds, rather dense, with clear horizontal bases and little vertical development.

2. Medium- dense clouds, with clear contours and with coiled tops, with moderate vertical development.

3. Powerful- with a pronounced vertical development, often in the form of high towers with multiple ledges.

4. Broken- small clouds with broken edges and rapidly changing outlines.

Flat, medium and broken types of clouds are colloidally stable clouds that do not form precipitation. Light to moderate precipitation falls from powerful cumulus clouds, especially in the tropics.
The process of development of cumulus clouds occurs during the transition from flat or broken clouds to medium and powerful ones, and cumulonimbus clouds can act as the final phase. From cumulonimbus clouds always fall precipitation in the form of heavy showers, sometimes with hail, they are thunderclouds. These clouds almost always contain ice crystals and liquid water, which provoke powerful electrical phenomena.

Related content:

This article lists and describes all types of clouds.

Cloud types

Upper clouds are formed in temperate latitudes above 5 km, in polar latitudes above 3 km, in tropical latitudes above 6 km. The temperature at this altitude is quite low, so they consist mainly of ice crystals. Upper clouds are usually thin and white. The most common form of upper clouds are cirrus (cirrus) and cirrostratus (cirrostratus), which can usually be observed in good weather.

Middle clouds usually located at an altitude of 2-7 km in temperate latitudes, 2-4 km in polar and 2-8 km in tropical latitudes. They consist mainly of small particles of water, but at low temperatures they can also contain ice crystals. The most common types of mid-tier clouds are altocumulus (altocumulus), altostratus (altostratus). They may have shaded portions, which distinguishes them from cirrocumulus clouds. This type of cloud usually results from air convection and also from the gradual rise of air ahead of a cold front.

Lower clouds located at altitudes below 2 km, where the temperature is quite high, so they consist mainly of water droplets. Only in the cold season. When the surface temperature is low, they contain particles of ice (hail) or snow. The most common types of low clouds are nimbostratus (nimbostratus) and stratocumulus (stratocumulus), dark low clouds accompanied by moderate precipitation.

Fig1. The main types of clouds: Cirrus, Ci), Cirrocumulus (Cirrocumulus, Cc), Cirrostratus, Cs, Altocumulus (Altocumulus, Ac), Altostratus, As, Altostratus translucidus , As trans) , Strato-nimbus (Nimbostratus, Ns), Stratus (Stratus, St) , Stratocumulus (Stratocumulus, Sc), Cumulus (Cumulus, Cu), Cumulonimbus (Cumulonimbus, Cb)

Pinnate (Cirrus, Ci)

They consist of separate pinnate elements in the form of thin white threads or white (or mostly white) tufts and elongated ridges. They have a fibrous structure and / or a silky sheen. They are observed in the upper troposphere, in the middle latitudes their bases most often lie at altitudes of 6-8 km, in the tropical from 6 to 18 km, in the polar from 3 to 8 km). Visibility within the cloud is 150-500 m. They are built from ice crystals large enough to have an appreciable falling speed; therefore, they have a significant vertical extent (from hundreds of meters to several kilometers). However, wind shear and differences in crystal size cause the filaments of cirrus clouds to be slanted and warped. These clouds are characteristic of the leading edge of a cloud system of a warm front or an occlusion front associated with an upward slip. They often also develop in anticyclonic conditions, sometimes they are parts or remnants of ice tops (anvils) of cumulonimbus clouds.

There are different types: filiform(Cirrus fibratus, Ci fibr.), claw-like(Cirrus uncinus, Ci unc.), turret-shaped(Cirrus castellanus, Ci cast.), dense(Cirrus spissatus, Ci spiss.), flaky(Cirrus floccus, Ci fl.) and varieties: mixed up(Cirrus intortus, Ci int.), radial(Cirrus radiatus, Cirad.), spinal(Cirrus vertebratus, Ci vert.), double(Cirrus duplicatus, Ci dupl.).

Sometimes this genus of clouds, along with the described clouds, also includes cirrostratus and cirrocumulus clouds.

Cirrocumulus (Cirrocumulus, Cc)

They are often referred to as "lambs". Very high small globular clouds, elongated in a line. Look like the backs of mackerels or ripples on the coastal sand. The height of the lower border is 6-8 km, the vertical length is up to 1 km, the visibility inside is 5509-10000 m. They are a sign of an increase in temperature. Often observed together with cirrus or cirrostratus clouds. They are often the forerunners of storms. With these clouds, the so-called. "iridization" - iridescent coloring of the edge of the clouds.

Cirrostratus, Cs

Halo formed on cirrus clouds

Sail-like clouds of the upper tier, consisting of ice crystals. They have the appearance of a homogeneous, whitish veil. The height of the lower edge is 6-8 km, the vertical extent varies from several hundred meters to several kilometers (2-6 or more), visibility inside the cloud is 50-200 m. Cirrostratus clouds are relatively transparent, so the sun or moon can be clearly visible through them. These upper tier clouds usually form when large layers of air rise up through multilevel convergence.

Cirrostratus clouds are characterized by the fact that they often give the phenomena of a halo around the sun or moon. Halos are the result of the refraction of light by the ice crystals that make up the cloud. Cirrostratus clouds, however, tend to thicken as a warm front approaches, which means more ice crystal formation. As a result, the halo gradually disappears, and the sun (or moon) becomes less visible.

Altocumulus (Altocumulus, Ac)

Formation of altocumulus clouds.

Altocumulus (Altocumulus, Ac) - typical warm season cloud cover. Gray, white, or bluish clouds in the form of waves and ridges, consisting of flakes and plates separated by gaps. The height of the lower boundary is 2-6 km, the vertical length is up to several hundred meters, the visibility inside the cloud is 50-80 m. They are usually located above the places facing the sun. Sometimes they reach the stage of powerful cumulus clouds. Altocumulus clouds usually form when warm air masses rise, as well as when a cold front advances, which pushes warm air upwards. Therefore, the presence of altocumulus clouds on a warm and humid summer morning portends the imminent appearance of storm clouds or a change in the weather.

High-stratified (Altostratus, As)

Altostratus clouds

They look like a uniform or weakly expressed wavy veil of gray or bluish color, the sun and moon usually shine through, but weakly. The height of the lower boundary is 3-5 km, the vertical extent is 1-4 km, the visibility in the clouds is 25-40 m. These clouds consist of ice crystals, supercooled water drops and snowflakes. Altostratus clouds can bring heavy rain or snow.

High-layered translucent (Altostratus translucidus, As trans)

Altostratus clouds at sunset

Altostratus translucent clouds. The wavy structure of the cloud is noticeable, the solar circle of the sun is quite distinguishable. Quite distinguishable shadows can sometimes appear on the ground. Stripes are clearly visible. A veil of clouds, as a rule, gradually covers the entire sky. The height of the base is within 3-5 km, the thickness of the As trans cloud layer is on average about 1 km, occasionally up to 2 km. Precipitation falls, but in low and middle latitudes it rarely reaches the ground in summer.

Nimbostratus (Nimbostratus, Ns)

Nimbostratus clouds and strong air currents.

Nimbostratus clouds are dark gray, in the form of a continuous layer. During precipitation, it seems to be homogeneous; in the intervals between precipitation, some heterogeneity and even some undulation of the layer are noticeable. From stratus clouds differ in a darker and bluish color, inhomogeneity of the structure and the presence of overlying sediments. The height of the lower boundary is 0.1-1 km, the thickness is up to several kilometers.

Layered (Stratus, St)

Layered clouds.

Layered clouds form a homogeneous layer, similar to fog, but located at a height of hundreds or even tens of meters. Usually they cover the entire sky, but sometimes they can be observed in the form of broken cloud masses. The lower edge of these clouds can drop very low; sometimes they merge with ground fog. Their thickness is small - tens and hundreds of meters.

Stratocumulus (Stratocumulus, Sc)

Gray clouds, consisting of large ridges, waves, plates, separated by gaps or merging into a continuous gray wavy cover. Composed primarily of water droplets. The thickness of the layer is from 200 to 800 m. The sun and moon can only shine through the thin edges of the clouds. Precipitation usually does not fall. From stratocumulus clouds that are not translucent, weak, short-term precipitation may fall.

Cumulus clouds (Cumulus, Cu)

Cumulus clouds. View from above.

Cumulus clouds are dense, bright white clouds during the day with significant vertical development (up to 5 km or more). The upper parts of cumulus clouds look like domes or towers with rounded outlines. Cumulus clouds usually form as convection clouds in cold air masses.

Cumulonimbus (Cumulonimbus, Cb)

Cumulonimbus (Cumulonimbus capillatus incus)

Cumulonimbus - powerful and dense clouds with a strong vertical development (up to a height of 14 km), giving heavy rainfall with powerful hail and thunderstorms. Cumulonimbus clouds/clouds develop from powerful cumulus clouds. They can form a line called a squall line. The lower levels of cumulonimbus clouds are mostly water droplets, while the higher levels, where temperatures are well below 0°C, are dominated by ice crystals.

Hello friends! Clouds, white-maned horses ... Oh, what am I talking about🙂Actually, I want to talk about how clouds form, where they form and what are the reasons for this, and what other types of clouds are ...

Masses of water vapor carried through the air are clouds. At any given time, about 50% of the earth's surface is covered by clouds. Clouds are also part of a process that provides fresh water all living things on .

When the vapor rises, it cools and again turns into a solid (ice) or liquid (water) state, forming clouds (invisible masses). In the form that is carried away by streams and rivers, moisture returns to Earth, and the cycle repeats.

How are clouds formed?

Clouds are made up of ice and/or water. Everywhere in there is water vapor, which evaporates from the oceans and seas. The "absolute humidity" of air determines the amount of steam in a given volume of air. The higher the temperature, the more water vapor can be contained in the air.

If the air contains the maximum possible amount of water vapor for a given temperature, it is considered "saturated", and its "relative humidity" is 100%. The "dew point" is the corresponding temperature. The process of changing water vapor into a solid or liquid state, which takes place when the air containing the vapor cools and becomes saturated, is called condensation.

Air cooling.

As a result of the rise, the air can cool, for example, when it flows over hills. At the same time, using part of its heat, it expands due to a pressure drop (“adiabatic expansion”). Clouds form when excess water vapor condenses into water droplets when the temperature drops to a certain point.

The main causes of air rise, which lead to its cooling, cloud formation and condensation: the first is turbulence caused by a sharp change in wind speed and direction and creating all the necessary conditions for cloud formation.

The second - when passing over the mountains and hills, the "spelling rise" of air. In this case, various types of clouds can form: a cloud cap, mountain fog, vortex, flag-like and lentil-shaped clouds.

When it cools down to the dew point wet air, before reaching the top, mountain fog appears. Everything is perceived as something that fell into such a cloud and clings to the top and windward side.

With rather dry air, which cools after rising above the top of the mountain to the dew point, a cloud cap forms. It seems that the cloud is hanging motionless over the top of the mountain, even despite the wind. This is not the same cloud, strictly speaking, it is constantly formed on the windward side and evaporates on the leeward side.

Pennant-like, flag-like clouds form over mountain peaks when air is forced to flow around the peak on both sides, creating turbulent lift sufficient to create clouds and eddies in the moist air currents on the lee side of the mountain.

The cloud that has formed behind the peak flows downwind and eventually evaporates. On the crests of undulating air currents that pass over rough terrain, lenticular undulating clouds often form.

A vortex cloud in the form of an elongated cylinder can form, located parallel to a mountain range on its leeward side in a turbulent vortex.

Convergence.

Inside huge weather systems - "cyclones" (areas of low pressure), air masses can also rise.

When, "fighting" for free space, warm wet masses "converge" (converge) with cold air masses - large ridges of clouds form. Up displaces lighter and warmer air - denser and colder. Often such a "front" brings prolonged rains and heavy rainfall.

The nature of the upward movement of air masses determines the shape of the clouds. Slowly ascending air currents (5 - 10 cm/sec.) usually form stratus clouds, and warm air - cumulus clouds, which rise from the surface at least 100 times faster than stratus clouds.

Scientists have found that in these clouds, air currents can rise at speeds of up to 100 km/h, and how high they rise depends largely on the "instability" or "stability" of the air through which they pass.

The air in the cloud cools by 1°C for every 100 m rise. “Stable” conditions are when the ambient air temperature drops at a high rate, while this stream continues to rise.

"Unstable Conditions" it is when ambient air cools more slowly, and the ascending currents soon reach the same temperature and the rise stops.

Cloud classification.

Clouds, influenced by the many processes involved in their formation, are different shapes, colors and sizes. Ancient scientists, long before they began to understand the reasons for the formation of clouds, tried to classify and describe their diversity.

Jean Baptiste Lamarck (1744 - 1829), the French founder of the theory of evolution, as well as a naturalist, was one of the first among them.

He proposed to classify clouds into five types and three levels in 1802. Lamarck believed that clouds formed as a result of a series of circumstances (although he did not know exactly what), and not by chance.

The English chemist Luke Howard, in the same 1802, developed a classification that included three main types of clouds, and also gave them Latin names: Stratus is stratiform, Cirrus is pinnate and Cumulus is cumulus.

And these basic terms are also used today. The first "international cloud atlas" was published in 1896. At that time, clouds were still considered to be non-developing, constant masses. But the fact that each cloud has its own life cycle became clear by the 1930s.

Today, the World Meteorological Organization (WMO) distinguishes 10 main types of clouds according to their shape and height. Each type has a common abbreviation.

Soaring above.

To upper clouds include cirrostratus (Cs), cirrocumulus (Cc) and cirrocumulus (Ci). They are composed of ice crystals, occur at altitudes of 6 to 18 km, and are not a source of precipitation that falls on Earth.

Cirrus clouds have the shape of individual thin white hairs. Wavy plates or white patches resemble cirrocumulus clouds. And on the transparent veil thrown to the sky, cirrostratus clouds look like.

Middle clouds - Altostratus (As) and Altocumulus (Ac) - consist of a mixture of ice crystals and water droplets, and are located at an altitude of 3 - 6 km. Altocumulus clouds look like white-gray broken plates, and altostratus clouds look like gray-blue whole sheets. Very little precipitation falls from mid-tier clouds.

Lower clouds (up to 3 km high) include Stratocumulus (Cs), Cumulus (Cu), Stratocumulus (Ns), Stratus (St), and Cumulonimbus (Cb). Cumulus, stratocumulus and stratus are made up of droplets, while stratonimbus and cumulonimbus are made up of a mixture of ice and water.

Stratus and stratocumulus clouds look like a gray canvas, but the former are a homogeneous layer, while the latter are more fragmented. They may come in drizzle or light rain. Nimbostratus clouds look like a dark gray layer, they carry snow or heavy rains.

Vertically rising cumulus clouds have clear outlines and a dense structure. They may be accompanied by showers. Cumulonimbus are dark, large and dense clouds (sometimes with an anvil-flat top) associated with thunderstorms and heavy rain.

Now, looking at the sky, you can understand what kind of clouds are there and what weather should be expected...

L. Tarasov

Like fogs, clouds are formed by the condensation of water vapor into liquid and solid states. Condensation occurs either due to an increase absolute humidity air, or as a result of a decrease in air temperature. In practice, both factors are involved in cloud formation.

Formation of clouds as a result of convection.

Cloud formation over warm atmospheric front.

Cloud formation over a cold atmospheric front.

The decrease in air temperature is due, firstly, to the rise (ascending movement) of air masses and, secondly, to the advection of air masses - their movement in a horizontal direction, due to which warm air can be above the cold earth's surface.

We confine ourselves to discussing the formation of clouds caused by a decrease in air temperature during an upward movement. It is obvious that such a process differs significantly from the formation of fog - after all, the fog practically does not rise up, it remains directly at the earth's surface.

What makes air rise up? There are four reasons for the upward movement of air masses. The first reason is the convection of air in the atmosphere. On a hot day Sun rays strongly warm the earth's surface, it transfers heat to the surface masses of air - and their rise begins. Cumulus and cumulonimbus clouds are most often of convective origin.

The process of cloud formation begins with the fact that some air mass rises. As you rise, the air will expand. This expansion can be considered adiabatic, since the air rises relatively quickly, and therefore, with a sufficiently large volume (and a really large volume of air is involved in the formation of a cloud), the heat exchange between the rising air and environment simply does not have time to occur during the ascent. During adiabatic expansion, air, without receiving heat from outside, does work only due to its own internal energy, and then cools down. So, the air rising up will be cooled.

When the initial temperature T 0 of the rising air drops to the dew point T p, corresponding to the elasticity of the vapor contained in it, the process of condensation of this vapor will become possible. In the presence of condensation nuclei in the atmosphere (and they are almost always present), this process really begins. The height H, at which vapor condensation begins, determines the lower boundary of the forming cloud. It is called the level of condensation. In meteorology, an approximate formula for the height H is used (the so-called Ferrel formula):

H \u003d 120 (T 0 -T p),

where H is measured in meters.

The air that continues to flow from below crosses the condensation level, and the process of steam condensation occurs already above this level - the cloud begins to develop in height. The vertical development of the cloud will stop when the air, having cooled, stops rising. In this case, a fuzzy upper boundary of the cloud will form. It is called the level of free convection. It is located slightly above the level at which the temperature of the rising air becomes equal to the temperature of the surrounding air.

The second reason for the rise of air masses is due to the terrain. The wind blowing along the earth's surface may meet mountains or other natural elevations on its way. Overcoming them, the air masses are forced to rise up. Formed in this case clouds are called clouds of orographic origin (from the Greek word oros meaning "mountain"). It is clear that such clouds do not receive a significant development in height (it is limited by the height of the elevation overcome by the air); in this case, stratus and nimbostratus clouds arise.

The third reason for the rise of air masses is the occurrence of warm and cold atmospheric fronts. Cloud formation occurs especially intensely over a warm front - when a warm air mass, advancing on a cold air mass, is forced to slide up a wedge of receding cold air. The frontal surface (the surface of the cold wedge) is very gentle - the tangent of its inclination to the horizontal surface is only 0.005-0.01. Therefore, the upward movement of warm air differs little from the horizontal movement; as a consequence, the cloudiness that arises above the cold wedge develops weakly in height, but has a significant horizontal extent. Such clouds are called upslip clouds. In the lower and middle tiers, these are nimbostratus and altostratus clouds, and in the upper tier - cirrostratus and cirrus (it is clear that the clouds of the upper tier are already formed far behind the atmospheric front line). The horizontal extent of upward slip clouds can be measured in hundreds of kilometers.

Cloud formation also occurs above a cold atmospheric front - when an advancing cold air mass moves under a mass of warm air and thereby raises it. In this case, cumulus clouds may also form in addition to upslip clouds.

The fourth reason for the rise of air masses is cyclones. air masses, moving along the surface of the earth, twist towards the center of the depression in the cyclone. Accumulating there, they create a pressure drop along the vertical and rush upward. Intense rise of air up to the border of the troposphere leads to powerful cloud formation - clouds of cyclonic origin appear. It can be stratified-nimbus, altostratus, cumulonimbus clouds. Precipitation falls from all such clouds, creating rainy weather characteristic of a cyclone.

Based on the book by L. V. Tarasov "Winds and thunderstorms in the Earth's atmosphere." - Dolgoprudny:Publishing House "Intellect", 2011.
Book Information publishing house"Intellect" - on the website