What are cumulus clouds formed from. Where do clouds come from? Formation of thunderclouds

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 air masses forced to go 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 stratified rain and high stratus clouds, and in the upper tier - cirro-stratified 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, along with upslip clouds, there may also be Cumulus 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 a 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 site

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Clouds can be classified as follows: stratus, cumulus and cirrus. Stratus clouds are observed when a wide band of air slowly rises above the surface of a warm front.

Cumulus clouds form when warm air is released from the soil or when the upper atmosphere is unstable due to cold air. Cirrus clouds, on the contrary, appear when ice crystals accumulated in the upper atmosphere fall down and are carried by local air currents. These three main varieties are often combined to form a long line additional types clouds.

Cumulus clouds slowly grow as air currents continue to rise. If their growth continues long enough, they can turn into cumulonimbus clouds.

The inversion layer flattens the cloud

If a temperature inversion layer (in which temperature increases with altitude) forms over a developing cloud, then the cloud may begin to grow horizontally (below), becoming stratocumulus. If the cloud expands under the influence of the stratosphere, it turns into a flat cumulonimbus cloud. Growth up or inward Clouds also differ depending on the height of their position above the Earth: lower, middle and upper. The upper clouds (detected at an altitude of 5-8 km) include cirrus, cirrostratus and cirrocumulus clouds. Medium clouds, which include altostratus, altocumulus and nimbostratus clouds, are located at an altitude of 2 to 7.3 km. Finally, clouds that form below 2 km are called lower clouds; these include stratus and stratocumulus. vertical clouds, formed when air is heated by the sun in the immediate vicinity of the surface, are cumulus and rain.

Curving clouds

Ice crystals from high-altitude cirrus clouds (right) can fall vertically if the speed of the air jets is the same at all altitudes. However, if there is a speed difference, they can bend or notch.

Altocumulus clouds (below) that form between layers of warm and cold, respectively, lower and upper air, sometimes take on a rounded shape. They are held between the downward air currents of the upper layer and the upward air currents of the lower one.

Altocumulus clouds

Layered clouds and rain

When raindrops fall on particularly warm areas of the earth's surface, some of them begin to evaporate already during the fall (below). If evaporation continues, the air can become saturated and form stratus clouds.

Clouds forming in waves

When horizontal air masses (below) move quickly in the upper atmosphere and slowly closer to the surface, their rotation creates undulating clouds.

wave crests

Wave clouds (right) can also be seen at the top of air currents that move between a dry warm layer above and a cold wet layer below.

Everyone has seen clouds. They are large and small, almost transparent and very thick, white or dark, pre-stormy. Taking different shape, they resemble animals and objects. But why do they look like that? We will talk about this below.

What is a cloud

Anyone who has flown in an airplane has probably "passed" through the cloud and noticed that it looks like fog, only it is not directly above the ground, but high in the sky. The comparison is quite logical, because both of them are ordinary steam. And it, in turn, consists of microscopic droplets of water. Where do they come from?

This water rises into the air as a result of evaporation from the surface of the earth and water bodies. Therefore, the greatest accumulation of clouds is observed over the seas. During the year, about 400 thousand cubic kilometers evaporate from their surface, which is 4 times higher than that of land.

What are there? It all depends on the state of the water that forms them. It can be gaseous, liquid or solid. It may seem surprising, but some clouds are actually made of ice.

We have already found out that clouds are formed as a result of the accumulation of a large number of water particles. But to complete the process, a link is needed, to which the drops will "stick" and come together. Often this role is played by dust, smoke or salt.

Classification

The height of the location largely determines what clouds are formed from and how they will look. As a rule, the white masses that we are used to seeing in the sky appear in the troposphere. Its upper limit varies depending on geographical location. The closer an area is to the equator, the higher standard clouds can form. For example, over an area with tropical climate the boundary of the troposphere is located at an altitude of about 18 km, and beyond the Arctic Circle - 10 km.

Cloud formation is also possible at high altitudes, but they are currently little studied. For example, mother-of-pearl appear in the stratosphere, and silver ones appear in the mesosphere.

Clouds of the troposphere are conditionally divided into types depending on the height at which they are located - in the upper, middle or lower tier troposphere. Air movement also has big influence for cloud formation. In a calm environment, cirrus and stratus clouds form, but if the tropospheres move unevenly, cumulus clouds are more likely to appear.

Upper tier

This gap covers the area of ​​the sky at an altitude of more than 6 km and up to the edge of the troposphere. Considering that the air temperature here does not rise above 0 degrees, it is easy to guess what clouds form in the upper tier. It can only be ice.

By appearance clouds located here are divided into 3 types:

1. Cirrus. They have a wavy structure and can look like individual threads, stripes or whole ridges.
2. cirrocumulus consist of small balls, curls or flakes.
3. Cirrostratus are a translucent likeness of a fabric that "covers" the sky. Clouds of this type can stretch over the entire sky or occupy only a small area.

The height of a cloud located in the upper tier can vary greatly depending on various factors. It can be several hundred meters or tens of kilometers.

Middle and lower tier

The middle tier is a part of the troposphere, usually located between 2 and 6 km. Here there are altocumulus clouds, which are three-dimensional gray or white masses. They are made up of water warm time year and, accordingly, from ice to cold. The second type of clouds are altostratus. They have and often completely cover the sky. Such clouds carry precipitation in the form of drizzle or light snow, but they rarely reach the surface of the earth.

The lower tier represents the sky directly above us. Clouds here can be of 4 types:

1. Stratocumulus in the form of blocks or shafts of gray color. Can carry precipitation, except when the temperature is too low.
2. layered. They are located below all the others, have a gray color.
3. Layered rain. As you can understand by the name, they carry precipitation, and, as a rule, they are of a continuous nature. These are gray clouds that do not have a specific shape.
4. Cumulus. One of the most recognizable clouds. They look like powerful heaps and clubs with an almost flat base. Such clouds do not bring precipitation.

There is another species that is not included in the general list. These are cumulonimbus clouds. They develop vertically and are present in each of the three tiers. Such clouds bring showers, thunderstorms and hail, so they are often called thunderclouds or showers.

Cloud Lifespan

For those who know what clouds form from, the question of their lifespan may also be of interest. Here great importance plays the humidity level. She is a kind of source vitality for clouds. If the air in the troposphere is dry enough, then the cloud cannot survive for long. If the humidity is high, it may hover in the sky longer until it becomes more powerful in order to produce precipitation.

As for the shape of the cloud, its life span is very short. Water particles tend to constantly move, evaporate and reappear. Therefore, the same cloud shape cannot be preserved even for 5 minutes.

The main reason for the formation of clouds is upward movement of air. During such movements, the air cools adiabatically and the water vapor contained in it reaches saturation and thickens: the upward movement in this case can be caused by various reasons: air heating from below from the underlying surface, sliding it along an inclined frontal surface and moving upward along the slopes of a hill, and more. An important factor in cloud formation is also turbulent motion. Due to which water vapor moves from the lower layers to the higher ones. An important role in the formation of clouds is also played by the cooling of air by radiation, as well as wave motions in the atmosphere on the surface of the inversion.

The primary products of cloud formation are usually water droplets. If clouds form in a layer with a temperature below 0, then they consist of supercooled droplets. Clouds made up of drops are called water. At sufficiently low negative temperatures, clouds consist of ice crystals and are called icy/crystal. Clouds can also consist simultaneously of supercooled water drops and ice crystals and are called mixed. The vertical power of these (mixed) clouds is great, especially in the case of their long existence, they significantly exceed the power of water and ice clouds. The smallest droplets of water and ice crystals that make up the clouds have negligible weight. The speed of their fall is very small and a slight upward movement of air is enough to make water droplets and ice crystals float in the air and even rise up. Clouds move horizontally with the help of wind. Clouds are higher in summer than in winter. As latitude increases, cloud height decreases.

Properties of clouds and their main genera.

According to the international classification, all clouds are divided into 4 families according to the nature of the structure and the height at which they form.

Upper clouds they are usually icy - these are thin, transparent, light clouds without a shadow of white. The sun shines through them, objects give a shadow.

Clouds of the middle and lower tiers usually are water or mixed. However, in winter, at sufficiently low negative temperatures, the clouds of these tiers can turn into icy ones. Medium clouds are denser than cirrus. They can cause colored crowns around the sun or moon.

Clouds of vertical development or convection clouds are formed by updrafts of air. Since convection over land in temperate latitudes occurs mainly in the warm season, when the air warms up significantly from below, from the underlying surface, then during this time the greatest frequency of clouds of vertical development is observed. Convection clouds have a diurnal course. Over land, these clouds appear in the summer and in the morning, reach their maximum development around noon, and disappear in the evening. Above the heated slopes of mountains and water, lowlands clouds of vertical development are formed more often than on the plains.

Cloud types:

- cirrus - separate thin light clouds of white color, often shiny, fibrous or drinking structure, they look like flakes, hooks, threads or feathers

- cirrocumulus clouds are small white flakes or small balls (lambs) resembling lumps of snow without shadows, arranged in groups or rows, often look like ripples / fish scales.

- cirro-stratified - a thin whitish veil of appearances, often covering the entire sky, giving it a milky-white hue, sometimes the veil reveals a fibrous structure. These clouds are the cause of the formation of optical phenomena - these are large colorless circles around the sun / moon. These circles are formed as a result of refraction and reflection of light in ice crystals.

- altocumulus - have the form of plates, balls, shafts of various sizes, white or gray, located in ridges, groups or layers going in one or two directions. Sometimes these clouds are arranged in parallel waves between cloud elements. Often, significant enlightenment or blue skies are visible.

- high-layered - represent a gray veil, this veil is often so thin that through it, as through frosted glass you can see the sun or moon in the form of blurry spots. They can give precipitation in the form of rain or snow, but in summer the precipitation from these clouds during the fall usually evaporates and does not reach the surface of the earth.

- stratocumulus - gray with dark parts, collected in groups, rows or shafts in one or two directions, gaps of blue sky are sometimes visible between cloud elements. Most often, clouds appear on land in winter. Often they cover the entire sky and give it a wavy appearance.

- stratus - these clouds represent a continuous uniform layer, light / dark gray, covering the sky and giving it an overcast look. These clouds can precipitate as drizzle or as very fine snow grains and ice needles.

- nimbostratus - low dense, dark gray clouds with broken edges. Heavy precipitation falls in the form of rain or snow. Sometimes precipitation does not reach the surface of the earth, i.e. evaporate along the way. In this case, bands of falling precipitation can be seen in the clouds.

- cumulus - dense clouds, strongly developed in height with a domed white top, with sharp round outlines and a horizontal gray / dark base. They do not give precipitation in our conditions. Sometimes they are torn by the wind into separate small pieces, such clouds are called broken - rain.

- cumulonimbus - powerful masses of swirling cumulus-shaped clouds with strong vertical development, looking like mountains or towers, the base of these clouds is dark.

Formation of convection, upward slip and wavy clouds.

From the point of view of the origin of the above genera of clouds, they can be divided into convection clouds, upward sliding clouds, and wavy clouds.

To convection clouds include cumulus and cumulonimbus clouds. They develop mainly with an unstable vertical distribution of temperature and occur mainly in the warm season. But cumulonimbus clouds sometimes form during the cold season. During the passage of a cold front, when cold air quickly leaks under the warm and the latter rapidly rises up. In this case, cumulonimbus clouds can produce flakes in the winter in early spring and flakes in late autumn.

Ascending clouds these include cirrus, cirrostratus, high-stratus, and nimbostratus. These clouds are formed by the upward sliding of warm air along sloping frontal surfaces. Such sliding is observed when a warm humid air under the warm one, when the latter is pushed up and starts to bump into the cold one. All these slips are slow and gradual, with such slips the air is adiabatically cooled (dramatically), which leads to a narrowing of the water vapor. As a result, a cloud system arises, the base of which coincides with the frontal surface. The clouds included in this system occupy a large space. In this cloud system, the highest are the cirrus, then the cirrostratus, below the high-stratus, and then the nimbostratus.

Education has a different character wavy clouds, i.e. clouds located in the sky in stripes, ridges or oxen, between which lighter parts of the cloud or gaps are visible blue sky. The wavy appearance has the following clouds: stratocumulus, altocumulus, cirrocumulus. These clouds form when two layers of air are located at the same height and have different temperatures, humidity and density. If these layers are mixed, then waves with a large length and a large amplitude appear at the boundary between them. However, such waves are unstable and turn into a series of vortices. The air that they capture, while developing into a large number of cells, and in each of them there is a movement of air up and down. Such cellular air circulation leads to the formation of wavy clouds.