White-maned horses. Where do clouds come from? In what part of the atmosphere do clouds form?

When water vapor condenses in the atmosphere at an altitude of several tens to hundreds of meters and even kilometers, clouds form.
This occurs as a result of the evaporation of water vapor from the Earth's surface and its lifting by rising currents of warm air. Depending on their temperature, clouds consist of water droplets or ice and snow crystals. These droplets and crystals are so small that they are retained in the atmosphere even by weak rising air currents.
The shape of clouds is very diverse and depends on many factors: height, wind speed, humidity, etc. At the same time, groups of clouds that are similar in shape and height can be distinguished. The most famous of them are cumulus, cirrus and stratus, as well as their varieties: stratocumulus, cirrostratus, nimbostratus, etc. Clouds supersaturated with water vapor, having a dark purple or almost black hue, are called clouds.

The degree of cloud coverage of the sky, expressed in points (from 1 to 10), is called cloudiness.
A high degree of cloudiness usually predicts precipitation. They are most likely to fall from altostratus, cumulonimbus and nimbostratus clouds.
Water that falls in a solid or liquid state in the form of rain, snow, hail, or condenses on the surface of various bodies in the form of dew or frost is called precipitation.

Rain is formed when the smallest droplets of moisture contained in a cloud merge into larger ones and, overcoming the force of rising air currents, fall to the Earth under the influence of gravity. If you find yourself in the cloud tiny particles solids, for example dust, the condensation process accelerates, since dust grains play the role of condensation nuclei.

In desert areas with low relative humidity, condensation of water vapor is possible only at high altitudes, where the temperature is lower, but rainfall evaporates in the air before reaching the ground. This phenomenon is called dry rains.
If condensation of water vapor in a cloud occurs at negative temperatures ah, precipitation forms in the form of snow.
Sometimes snowflakes from the upper layers of the cloud fall to its lower part, where the temperature is higher and there is a huge amount of supercooled water droplets held in the cloud by rising air currents. Connecting with water droplets, snowflakes lose their shape, their weight increases, and they fall to the ground in the form of a snowstorm - spherical snow lumps with a diameter of 2-3 mm.
A necessary condition for the formation of hail is the presence of a cloud of vertical development, the lower edge of which is in the zone of positive temperatures, and the upper edge is in the zone of negative temperatures (Fig. 36). Under these conditions, the resulting snowstorm rises in ascending currents to the zone of negative temperatures, where it turns into a spherical piece of ice - a hailstone. The process of raising and lowering a hailstone can occur repeatedly and is accompanied by an increase in its mass and size. Finally, the hailstone, overcoming the resistance of the rising air currents, falls to the ground. Hailstones vary in size: they can be from the size of a pea to a chicken egg.

Rice. 36. Scheme of hail formation in clouds of vertical development

Quantity atmospheric precipitation measured using a rain gauge. Long-term observations of the amount of precipitation made it possible to establish general patterns their distribution over the Earth's surface.
Largest quantity precipitation falls in the equatorial zone - on average 1500-2000 mm. In the tropics their number decreases to 200-250 mm. IN temperate latitudes There is an increase in precipitation to 500-600 mm, and in the polar regions the amount does not exceed 200 mm per year.
There is also significant unevenness in precipitation within the belts. It is determined by the direction of the winds and the features of the terrain.
For example, 1000 mm of precipitation falls on the western slopes of the Scandinavian mountains, and more than two times less on the eastern slopes. There are places on Earth where there is practically no precipitation. For example, in the Atacama Desert, precipitation falls once every few years, and according to long-term data, its value does not exceed 1 mm per year. It is also very dry in the Central Sahara, where the average annual precipitation is less than 50 mm.
At the same time, gigantic amounts of precipitation fall in some places. For example, in Cherrapunji - on the southern slopes of the Himalayas it falls up to 12,000 mm, and in some years - up to 23,000 mm, on the slopes of Mount Cameroon in Africa - up to 10,000 mm.
Precipitation such as dew, frost, fog, frost, ice is not formed in upper layers atmosphere, but in its surface layer. Cooling from the Earth's surface, the air can no longer hold water vapor; it condenses and settles on surrounding objects. This is how dew is formed. When the temperature of objects located near the Earth's surface is below 0 °C, frost forms.
When warmer air moves in and comes into contact with cold objects (most often wires, tree branches), frost forms - a coating of loose crystals of ice and snow.
When water vapor is concentrated in the surface layer of the atmosphere, fog is formed. Fogs are especially frequent in large industrial centers, where droplets of water, merging with dust and gases, form a toxic mixture - smog.
When the temperature of the Earth's surface is below 0 °C, and precipitation falls from the upper layers in the form of rain, black ice begins. Freezing in the air and on objects, droplets of moisture form an ice crust. Sometimes there is so much ice that wires break and tree branches break under its weight. Black ice on roads and winter pastures is especially dangerous. Black ice looks like black ice. But it is formed differently: liquid precipitation falls on the ground, and when the temperature drops below 0 ° C, the water on the ground freezes, forming a slippery ice film.

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

What is a cloud

Anyone who has flown an airplane has probably “passed” through a 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 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. Over the course of a year, about 400 thousand cubic kilometers evaporate from their surface, which is 4 times higher than that of land.

What are they? 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 connecting link is needed to which the drops will “stick” and gather together. Often this role is played by dust, smoke or salt.

Classification

The altitude of the location largely determines what clouds are formed from and what they will look like. 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 the 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 approximately 18 km, and beyond the Arctic Circle - 10 km.

Cloud formation is also possible at high altitudes, but they are currently poorly studied. For example, pearlescent ones appear in the stratosphere, and silvery ones appear in the mesosphere.

Tropospheric clouds are conventionally divided into types depending on the altitude at which they are located - in the upper, middle or lower tier of the troposphere. Air movement also has a big influence on cloud formation. In calm environments, cirrus and stratus clouds form, but if the troposphere moves unevenly, the likelihood of cumulus clouds increases.

Upper tier

This gap covers a section of the sky at an altitude of more than 6 km and 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 in the upper tier are formed from. It can only be ice.

By appearance The clouds located here are divided into 3 types:

1. Cirrus. They have a wavy structure and can look like individual threads, stripes or entire ridges.
2. Cirrocumulus consist of small balls, curls or flakes.
3. Cirrostratus They represent a translucent semblance of fabric “covering” the sky. These types of clouds can stretch across the entire sky or occupy only a small area.

The height of the cloud 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 layer is a part of the troposphere, usually located between 2 and 6 km. Altocumulus clouds are found here, which are voluminous gray or white masses. They consist of water in the warm season and, accordingly, ice in the cold season. The second type of cloud is 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 gray. Precipitation may occur unless temperatures are too low.
2. Layered. They are located below all the others and are gray in color.
3. Nimbostratus. As can be understood by the name, they carry precipitation, and, as a rule, they are of a blanket nature. These are gray clouds that do not have a specific shape.
4. Cumulus. Some 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 one more 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 thunderstorms or showers.

Cloud Lifespan

For those who know what clouds are formed from, the question of their lifespan may also be interesting. Here great value plays a role in humidity levels. It is a kind of source of vitality for the clouds. If the air in the troposphere is dry enough, the cloud will not last long. If the humidity is high, it can float in the sky longer until it becomes more powerful to produce precipitation.

As for the shape of the cloud, its lifespan is very short. Water particles tend to constantly move, evaporate and appear again. Therefore, the same cloud shape cannot be maintained even for 5 minutes.

L. Tarasov

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

Cloud formation as a result of convection.

Formation of clouds above a warm atmospheric front.

Cloud formation over a cold front.

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

Let us limit ourselves to discussing the formation of clouds caused by a decrease in air temperature during upward movement. Obviously, such a process differs significantly from the formation of fog - after all, the fog practically does not rise upward, it remains directly at earth's surface.

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

The process of cloud formation begins with the fact that some air mass rises upward. 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 the formation of the cloud actually involves large volume air) heat exchange between rising air and environment It just doesn’t have time to happen during the ascent. During adiabatic expansion, air, without receiving heat from the outside, does work only due to its own internal energy, and then cools. So, the air rising 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, it will become possible process condensation of this steam. If there are condensation nuclei in the atmosphere (and they are almost always present), this process actually begins. The height H at which steam condensation begins determines the lower boundary of the forming cloud. This is called the condensation level. In meteorology, an approximate formula for height H is used (the so-called Ferrel formula):

H = 120(T 0 -T r),

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 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 vaguely defined 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 encounter mountains or other natural elevations along its path. Overcoming them, air masses are forced to rise upward. The clouds formed in this case are called clouds of orographic origin (from the Greek word oros, meaning “mountain”). It is clear that such clouds do not receive significant development in height (it is limited by the height of the elevation overcome by the air); in this case, stratus and nimbostratus clouds appear.

The third reason for the rise of air masses is the emergence 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 retreating cold air. The frontal surface (the surface of the cold wedge) is very flat - the tangent of its angle of inclination to the horizontal surface is only 0.005-0.01. That's why upward movement warm air differs little from horizontal movement; As a result, the cloudiness that appears above the cold wedge develops weakly in height, but has a significant horizontal extent. Such clouds are called ascending clouds. In the lower and middle tiers these are nimbostratus and altostratus clouds, and in the upper tier these are cirrostratus and cirrus (it is clear that the clouds of the upper tier are formed far behind the atmospheric front line). The horizontal extent of ascending 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 lifts it. In this case, along with ascending clouds, cumulus clouds may also appear.

The fourth reason for the rise of air masses is cyclones. Air masses, moving along the surface of the earth, swirl towards the center of the depression in the cyclone. Accumulating there, they create a vertical pressure difference and rush upward. The intense rise of air up to the boundary of the troposphere leads to powerful cloud formation - clouds of cyclonic origin appear. These can be nimbostratus, altostratus, or 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.
Information about books from the Intellect publishing house is on the website

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

The primary products in cloud formation are usually water droplets. If clouds form in a layer with a temperature below 0, then they consist of supercooled drops. Clouds made up of droplets are called water. At sufficiently low negative temperatures, clouds consist of ice crystals and are called icy/crystalline. Clouds can also consist of both supercooled water droplets and ice crystals and are called mixed. The vertical power of these clouds (mixed) is large, especially if they exist for a long time, they significantly exceed the power of water and ice clouds. The smallest droplets of water and ice crystals that make up clouds have negligible weight. Their falling speed is very low and a weak upward movement of air is enough to make water droplets and ice crystals float in the air and even rise upward. With the help of wind, clouds move horizontally. The height of clouds in summer is greater 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 based on the nature of their structure and the height at which they form.

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

Middle and lower clouds Usually they are water or mixed. However, in winter, at sufficiently low negative temperatures, the clouds of these tiers can turn into ice. Medium clouds are denser than cirrus. They can create colored crowns around the sun or moon.

Clouds of vertical development or convection clouds are formed by rising air currents. 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, the greatest frequency of clouds of vertical development is observed during this time. Convection clouds have a diurnal cycle. Over land, these clouds appear in the summer and in the morning, reach their greatest development around midday, and disappear in the evening. Over the heated slopes of mountains and water, lowlands, clouds of vertical development are formed more often than on the plains.

Types of clouds:

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

- Cirrocumulus clouds are small white flakes or small balls (lambs) that resemble lumps of snow without shadows, are located in groups or rows, and often have the appearance of ripples/fish scales.

- cirrostratus - a thin whitish veil of appearance, often covering the entire sky, giving it a milky white tint; sometimes the veil reveals a fibrous structure. These clouds are the cause of the formation of optical phenomena - these are large colorless circles near the sun/moon. These circles are formed as a result of the 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 running in one or two directions. Sometimes these clouds are arranged parallel to the waves between the cloud elements. Often, significant clearing or blue sky is visible.

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

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

- stratus - these clouds represent a continuous homogeneous layer, light/dark gray in color, covering the sky and giving it an overcast appearance. These clouds can produce precipitation in the form of drizzle or in the form of very fine snow grains and ice needles.

- nimbostratus - low dense, dark gray clouds with torn edges. 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, streaks of falling precipitation may be visible in the clouds.

- cumulus - dense clouds, highly developed in height with a dome-shaped white top, with sharp round outlines and a horizontal gray/dark base. In our conditions they do not produce precipitation. Sometimes they are torn by the wind into separate small pieces; such clouds are called torn - rain.

- cumulonimbus - powerful masses of swirling cumulonimbus clouds with strong vertical development, having the appearance of mountains or towers, the base of these clouds is dark.

Formation of convection, upslip and wavy clouds.

From the point of view of origin, the above types of clouds can be divided into convective clouds, upslip clouds and wavy clouds.

TO convection clouds include cumulus and cumulonimbus clouds. They develop mainly under unstable vertical temperature distribution 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 flows under warm air and the latter rises violently. In this case, cumulonimbus clouds may appear in the form of flakes in winter early spring and late autumn cereals.

Rising clouds These include cirrus, cirrostratus, altostratus and nimbostratus. These clouds form when warm air glides upward along sloping frontal surfaces. Such sliding is observed when warm, moist air flows under the warm air, when the latter is forced upward and begins to bump into the cold air. All these slips occur slowly and gradually; during such slips, the air cools adiabatically (sharply), which leads to a narrowing of 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 cirrus, followed by cirrostratus, lower altostratus, and then nimbostratus.

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

Cumulus clouds - dense, bright white clouds during the day with significant vertical development. Associated with the development of convection in the lower and partially middle troposphere.

Most often, cumulus clouds appear in cold air masses in the rear of a cyclone, but are often observed in warm air masses in cyclones and anticyclones (except for the central part of the latter).

In temperate and high latitudes they are observed mainly in the warm season (the second half of spring, summer and first half of autumn), and in the tropics all year round. As a rule, they appear in the middle of the day and disappear in the evening (although they can also be observed over the seas at night).

Types of cumulus clouds:

Cumulus clouds are dense and well developed vertically. They have white dome-shaped or cumulus-shaped tops with a flat base that is grayish or bluish in color. The outlines are sharp, but in strong gusty winds the edges can become torn.

Cumulus clouds are located in the sky in the form of individual rare or significant accumulations of clouds that cover almost the entire sky. Individual cumulus clouds are usually scattered randomly, but can form ridges and chains. Moreover, their bases are at the same level.

The height of the lower boundary of cumulus clouds strongly depends on the humidity of the surface air and most often ranges from 800 to 1500 m, and in dry air masses (especially in steppes and deserts) it can be 2-3 km, sometimes even 4-4.5 km.

Causes of cloud formation. Condensation level (dew point)

The air in the atmosphere always contains some amount of water vapor, which is formed as a result of the evaporation of water from the surface of land and ocean. The rate of evaporation depends primarily on temperature and wind. The higher the temperature and the greater the steam capacity, the greater the evaporation.

Air can accept water vapor up to known limit until it becomes rich. If saturated air is heated, it will again acquire the ability to accept water vapor, i.e. it will again become unsaturated. As unsaturated air cools, it approaches saturation. Thus, the ability of air to contain more or less water vapor depends on temperature

The amount of water vapor contained in the air in at the moment(in g per 1 m3), called absolute humidity.

The ratio of the amount of water vapor contained in the air at a given moment to the amount that it can contain at a given temperature is called relative humidity and is measured as a percentage.

The moment of transition of air from an unsaturated state to a saturated state is called dew point(level of condensation). The lower the air temperature, the less water vapor it can contain and the higher the relative humidity. This means that when the air is cold, the dew point reaches the dew point faster.

When the dew point reaches, i.e. when the air is completely saturated with water vapor, when the relative humidity approaches 100%, water vapor condensation– the transition of water from a gaseous state to a liquid state.

When water vapor condenses in the atmosphere at an altitude of several tens to hundreds of meters and even kilometers, clouds.

This occurs as a result of the evaporation of water vapor from the Earth's surface and its lifting by rising currents of warm air. Depending on their temperature, clouds consist of water droplets or ice and snow crystals. These droplets and crystals are so small that they are retained in the atmosphere even by weak rising air currents. Clouds that are supersaturated with water vapor and have a dark purple or almost black tint are called clouds.

Structure of a cumulus cloud crowning an active TVP

Air currents in cumulus clouds

The thermal flow is a column of rising air. The rising warm air is replaced by cold air from above and zones of downward air movement are formed along the edges of the air flow. The stronger the flow, i.e. The faster the warm air rises, the faster the replacement occurs and the faster the cold air descends along the edges.

These processes naturally continue in the clouds. Warm air rises, cools and condenses. Droplets of water, together with cold air from above, fall down, replacing warm air. The result is a vortex movement of air with a strong rise in the center and an equally strong downward movement at the edges.

Formation of thunderclouds. Life cycle of a thundercloud

The necessary conditions for the emergence of a thundercloud are the presence of conditions for the development of convection or another mechanism that creates upward flows, a supply of moisture sufficient for the formation of precipitation, and the presence of a structure in which some of the cloud particles are in a liquid state, and some are in an icy state. There are frontal and local thunderstorms: in the first case, the development of convection is caused by the passage of a front, and in the second, by uneven heating of the underlying surface within one air mass.

Can be broken life cycle thundercloud into several stages:

• the formation of cumulonimbus clouds and its development due to the instability of the local air mass and convection: the formation of cumulonimbus clouds;
• the maximum phase of development of a cumulonimbus cloud, when the most intense precipitation, squally winds during the passage of a thunderstorm front, and the most severe thunderstorm are observed. This phase is also characterized by intense downward air movements;
• destruction of a thunderstorm (destruction of cumulonimbus clouds), reduction in the intensity of precipitation and thunderstorms until they cease).

So, let's look in more detail at each stage of thunderstorm development.

Cumulus cloud formation

Suppose, as a result of the passage of a front or intense heating of the underlying surface sun rays, convection air movement occurs. When the atmosphere is unstable, warm air rises. Rising upward, the air cools adiabatically, reaching a certain temperature at which condensation of the moisture contained in it begins. Clouds begin to form. During condensation, there is a release of thermal energy sufficient for further rise of air. In this case, a cumulus cloud develops vertically. The speed of vertical development can range from 5 to 20 m/s, so the upper limit of the formed cumulonimbus cloud, even in the local air mass, can reach 8 or more kilometers above the earth's surface. Those. within about 7 minutes, a cumulus cloud can grow to altitudes of about 8 km and turn into a cumulonimbus cloud. As soon as a cumulus cloud growing vertically has passed the zero isotherm (freezing temperature) at a certain altitude, ice crystals begin to appear in its composition, although total quantity drops (already supercooled) dominates. It should be noted that even at temperatures of minus 40 degrees, supercooled drops of water can occur. At the same moment, the process of precipitation formation begins. As soon as precipitation begins to fall from the cloud, the second stage of the evolution of a lightning storm begins.

Maximum phase of thunderstorm development

At this stage, the cumulonimbus cloud has already reached its maximum vertical development, i.e. reached the “locking” layer of more stable air - the tropopause. Therefore, instead of vertical development, the top of the cloud begins to develop in the horizontal direction. A so-called “anvil” appears, which is cirrus clouds consisting of ice crystals. In the cloud itself, convective currents form upward flows of air (from the base to the top of the cloud), and precipitation causes downward flows (directed from the top of the cloud to its base, and then even to the earth’s surface). Precipitation cools the air adjacent to it, sometimes by 10 degrees. The air becomes denser, and its fall to the surface of the earth intensifies and becomes more rapid. At such a moment, usually in the first minutes of a rainstorm, squally winds can be observed near the ground, dangerous for aviation and capable of causing significant destruction. They are sometimes mistakenly called “tornadoes” in the absence of a real tornado. The most intense thunderstorms are observed at this time. Precipitation leads to the predominance of downward air currents in a thundercloud. The third and final stage of the evolution of a thunderstorm begins - the destruction of a thunderstorm.

Lightning storm destruction

The ascending air currents in a cumulonimbus cloud are replaced by downward currents, thereby blocking the access of warm and moist air responsible for the vertical development of the cloud. The thundercloud is completely destroyed, and in the sky there remains only an “anvil” consisting of cirrus clouds, which is absolutely unpromising from the point of view of the formation of a thunderstorm.

Dangers associated with flying near cumulus clouds

As mentioned above, clouds are formed due to the condensation of rising warm air. Near the lower edge of cumulus clouds, warm air accelerates because The ambient temperature drops and replacement occurs faster. The hang glider, picking up in this warm air flow, may miss the moment when it horizontal speed even higher than the rate of ascent, and be pulled along with the rising air into the cloud.

In a cloud, due to the high concentration of water droplets, visibility is practically zero; accordingly, the hang glider instantly loses orientation in space and can no longer tell where and how he is flying.

In the worst case scenario, if warm air rises very quickly (for example, in a thundercloud), the hang glider can accidentally fall into an adjacent zone of rising and falling air, which will lead to a somersault and, most likely, destruction of the device. Or the pilot will be raised to heights with severe subzero temperatures and thin air.

Analysis and short-term weather forecasting. Atmospheric fronts. External signs of approaching cold and warm fronts

In previous lectures, I talked about the possibility of predicting flying and non-flying weather, the approach of one or another atmospheric front.

I remind you that atmospheric front - this is a transition zone in the troposphere between adjacent air masses with different physical properties.

When replacing and mixing one mass of air with another with different physical properties - temperature, pressure, humidity - various natural phenomena, which can be used to analyze and predict the movement of these air masses.

Thus, when a warm front approaches within a day, its harbingers appear - cirrus clouds. They float like feathers at an altitude of 7-10 km. At this time atmospheric pressure goes down. The arrival of a warm front is usually associated with warming and heavy, drizzling precipitation.

On the contrary, the onset of a cold front is associated with stratocumulus rain clouds, piling up like mountains or towers, and precipitation from them falls in the form of showers with squalls and thunderstorms. The passage of a cold front is associated with colder temperatures and stronger winds.

Cyclones and anticyclones

The earth rotates and moving air masses are also involved in this circular motion, twisting in a spiral. These huge atmospheric eddies are called cyclones and anticyclones.

Cyclone- an atmospheric vortex of huge diameter with reduced air pressure in the center.

Anticyclone– atmospheric vortex with high blood pressure air in the center, with a gradual decrease from the central part to the periphery.

We can also predict the onset of a cyclone or anticyclone based on weather changes. Thus, a cyclone brings with it cloudy weather with rain in the summer and snowfall in the winter. And an anticyclone means clear or partly cloudy weather, calm wind and lack of precipitation. The weather is stable, i.e. it does not change noticeably over time. From the point of view of flights, of course, anticyclones are more interesting to us.

Cold front. Cloud structure in a cold front

Let's go back to the fronts again. When we say that a cold front is “coming”, we mean that a large mass of cold air is moving towards warmer air. Cold air is heavier, warm air is lighter, so the advancing cold mass seems to creep under the warm one, pushing it upward. This creates a strong upward air movement.

The rapidly rising warm air cools in the upper layers of the atmosphere and condenses, causing clouds to appear. As I already said, there is a steady upward movement of air, so the clouds, having a constant supply of warm moist air, grow upward. Those. The cold front brings cumulus, stratocumulus and nimbus clouds with good vertical development.

The cold front moves, the warm front is pushed upward, and the clouds become oversaturated with condensed moisture. At some point, it pours down in showers, as if dumping the excess until the force of the upward movement of warm air again exceeds the gravity of the water drops.

Warm front. Cloud structure in a warm front

Now imagine the opposite picture: warm air moves towards cold air. Warm air is lighter and when moving it creeps onto cold air, atmospheric pressure drops, because. again, the column of lighter air presses less.

As the warm air rises through the cold air, it cools and condenses. Cloudiness appears. But the upward movement of air does not occur: the cold air has already spread below, there is nothing for it to push out, the warm air is already at the top. Because There is no upward movement of air, warm air cools evenly. The cloud cover is continuous, without any vertical development - cirrus clouds.

Hazards associated with the advance of cold and warm fronts

As I said earlier, the onset of a cold front is characterized by a powerful upward movement of warm air and, as a result, the redevelopment of cumulus clouds and thunderstorm formation. In addition, a sharp change in the upward movement of warm air and the adjacent downward movement of cold air, trying to replace it, leads to severe turbulence. The pilot feels this as a strong bump with sharp sudden rolls and lowering/raising of the nose of the aircraft.

In the worst case, turbulence can lead to a somersault; in addition, the processes of takeoff and landing of the device are complicated; flying near slopes requires greater concentration.

Frequent and severe thunderstorms can drag in an inattentive or carried away pilot, and a somersault will occur already in the cloud, being thrown to a great height, where it is cold and there is no oxygen - and possible death.

A warm front is unsuitable for good soaring flights and does not pose any danger, except perhaps the danger of getting wet.

Secondary fronts

The division within the same air mass, but between regions of air of different temperatures, is called secondary front. Secondary cold fronts are found near the Earth's surface in pressure troughs (areas low blood pressure) in the rear of the cyclone behind the main front, where the wind converges.

There can be multiple secondary cold fronts, each separating cold air from colder air. The weather on a secondary cold front is similar to the weather on a cold front, but due to smaller temperature contrasts, all weather phenomena are less pronounced, i.e. clouds are less developed, both vertically and horizontally. Precipitation zone, 5-10 km.

In summer, secondary cold fronts are dominated by cumulonimbus clouds with thunderstorms, hail, squalls, strong wind and icing, and in winter there are general snowstorms and snow charges that impair visibility to less than 1 km. The vertical front develops up to 6 km in summer, and up to 1-2 km in winter.

Occlusion fronts

Occlusion fronts are formed as a result of the closure of cold and warm fronts and the displacement of warm air upward. The closure process occurs in cyclones, where the cold front, moving with high speed, overtakes the warm one. In this case, warm air breaks away from the ground and is pushed upward, and the front near the earth's surface moves, essentially already under the influence of the movement of two cold air masses.

It turns out that three air masses are involved in the formation of the occlusion front - two cold and one warm. If the cold air mass behind the cold front is warmer than the cold mass in front of the front, then it, displacing warm air upward, will simultaneously flow onto the front, colder mass. This front is called warm occlusion(Fig. 1).

Rice. 1. Warm occlusion front on a vertical section and on a weather map.

If the air mass behind the cold front is colder than the air mass in front warm front, then this rear mass will flow under both the warm and the front cold air mass. This front is called cold occlusion(Fig. 2).

Rice. 2. Cold occlusion front on a vertical section and on a weather map.

Occlusion fronts go through a number of stages in their development. The most difficult weather conditions on occlusion fronts are observed at the initial moment of closure of the thermal and cold fronts. During this period, the cloud system is a combination of warm and cold front clouds. Precipitation of a blanket nature begins to fall from nimbostratus and cumulonimbus clouds; in the frontal zone they turn into showers.

The wind intensifies before the warm front of the occlusion, weakens after its passage and turns to the right.

Before the cold front of the occlusion, the wind intensifies to a storm, after its passage it weakens and sharply turns to the right. As warm air is displaced into higher layers, the occlusion front gradually blurs, the vertical power of the cloud system decreases, and cloudless spaces appear. Nimbostratus clouds gradually change to stratus, altostratus to altocumulus, and cirrostratus to cirrocumulus. Precipitation stops. The passage of old occlusion fronts is manifested in the influx of altocumulus clouds of 7-10 points.

The conditions for swimming through the zone of the occlusion front in the initial stage of development are almost no different from the conditions for swimming, respectively, when crossing the zone of warm or cold fronts.

Intramass thunderstorms

Thunderstorms are generally classified into two main types: intramass and frontal. The most common thunderstorms are intramass (local) thunderstorms, which occur far from frontal zones and are caused by the characteristics of local air masses.

Intramass thunderstorm is a thunderstorm associated with convection within an air mass.

The duration of such thunderstorms is short and, as a rule, is no more than one hour. Local thunderstorms can be associated with one or more cumulonimbus cloud cells and go through the standard stages of development: cumulonimbus initiation, development into thunderstorm, precipitation, disintegration.

Typically, intramass thunderstorms are associated with a single cell, although multicell intramass thunderstorms also occur. In multicell thunderstorm activity, downdrafts of cold air from the “mother” cloud create updrafts that form the “daughter” thundercloud. In this way, a series of cells can form.

Signs of improving weather

1. The air pressure is high, hardly changes or increases slowly.
2. The diurnal variation in temperature is sharply expressed: hot during the day, cool at night.
3. The wind is weak, intensifies in the afternoon, and subsides in the evening.
4. The sky is cloudless all day or covered with cumulus clouds, disappearing in the evening. Relative humidity air decreases during the day and increases towards night.
5. During the day the sky is bright blue, twilight is short, the stars twinkle faintly. In the evening the dawn is yellow or orange.
6. Heavy dew or frost at night.
7. Fogs over lowlands, increasing at night and disappearing during the day.
8. At night it is warmer in the forest than in the field.
9. Smoke rises from chimneys and fires.
10. Swallows fly high.

Signs of worsening weather

1. The pressure fluctuates sharply or continuously decreases.
2. The daily variation of temperature is weakly expressed or with a violation of the general variation (for example, at night the temperature rises).
3. The wind intensifies, abruptly changes its direction, the movement of the lower layers of clouds does not coincide with the movement of the upper ones.
4. Cloudiness is increasing. Cirrostratus clouds appear on the western or southwestern side of the horizon and spread throughout the sky. They give way to altostratus and nimbostratus clouds.
5. It's stuffy in the morning. Cumulus clouds grow upward, turning into cumulonimbus - to a thunderstorm.
6. Morning and evening dawns are red.
7. By night the wind does not subside, but intensifies.
8. Light circles (halos) appear around the Sun and Moon in cirrostratus clouds. There are crowns in the middle-tier clouds.
9. There is no morning dew.
10. Swallows fly low. Ants hide in anthills.

Stationary waves

Stationary waves- This is a type of transformation of horizontal air movement into wave-like. A wave can occur when fast-moving air masses meet mountain ranges of considerable height. A necessary condition for the occurrence of a wave is the stability of the atmosphere extending to a considerable height.

To see the atmospheric wave pattern, you can walk up to a stream and watch the flow around a submerged rock. Water, flowing around the stone, rises in front of it, creating something like fiberboard. Behind the stone, ripples or a series of waves are formed. These waves can be quite large in a fast and deep stream. Something similar happens in the atmosphere.

When flowing over a mountain range, the speed of the flow increases, and the pressure in it drops. Therefore, the upper layers of air decrease somewhat. Having passed the top, the flow reduces its speed, the pressure in it increases, and some of the air rushes upward. Such an oscillatory pulse can cause a wave-like movement of the flow behind the ridge (Fig. 3).

Rice. 3. Scheme of formation of stationary waves:
1 - undisturbed flow; 2 - downward flow over an obstacle; 3 - lenticular cloud at the top of the wave; 4 - cap cloud; 5 - rotor cloud at the base of the wave

These stationary waves often travel to high altitudes. The evaporation of a glider in a wave flow to a height of more than 15,000 m has been recorded. The vertical wave speed can reach tens of meters per second. The distances between neighboring “bumps” or wavelength range from 2 to 30 km.

The air flow behind the mountain is divided in height into two layers that differ sharply from each other - a turbulent sub-wave layer, whose thickness ranges from several hundred meters to several kilometers, and a laminar wave layer located above it.

It is possible to use wave flows if there is a second sufficiently high ridge in the turbulent zone and at such a distance that the rotor zone from the first does not affect the second ridge. In this case, the pilot, starting from the second ridge, immediately enters the wave zone.

When there is sufficient air humidity, lenticular clouds appear at the tops of the waves. The lower edge of such clouds is located at an altitude of at least 3 km, and their vertical development reaches 2 - 5 km. It is also possible for a cap cloud to form directly above the mountain top and rotor clouds behind it.

Despite the strong wind (a wave can occur at a wind speed of at least 8 m/s), these clouds are motionless relative to the ground. When a certain “particle” of the air flow approaches the top of a mountain or wave, the moisture contained in it condenses and a cloud is formed.

Behind the mountain, the formed fog dissolves, and the stream “particle” becomes transparent again. Above the mountain and at the tops of the waves, the speed of the air flow increases.

At the same time, the air pressure decreases. From school course physics ( gas laws) it is known that with a decrease in pressure and in the absence of heat exchange with the environment, the air temperature decreases.

A decrease in air temperature leads to moisture condensation and the formation of clouds. Behind the mountain the flow slows down, the pressure in it increases, and the temperature rises. The cloud disappears.

Stationary waves can also appear over flat terrain. In this case, the cause of their formation may be a cold front or vortices (rotors) that arise at different speeds and directions of movement of two adjacent layers of air.

Weather in the mountains. Features of weather changes in the mountains

The mountains are closer to the sun and, accordingly, warm up faster and better. This leads to the formation of strong convection currents and the rapid formation of clouds, including thunderstorms.

In addition, mountains are a significantly rugged part of the earth's surface. The wind, passing over the mountains, is turbulized as a result of bending around many obstacles different sizes- from a meter (stones) to a couple of kilometers (the mountains themselves) - and as a result of mixing of passing air by convection currents.

So, mountainous areas are characterized by strong thermal conditions combined with strong turbulence and strong winds different directions, thunderstorm activity.

Analysis of incidents and preconditions related to meteorological conditions

The most classic incident associated with meteorological conditions is the blowing away or independent flying of the apparatus into the rotor zone in the leeward part of the mountain (on a smaller scale - the rotor from an obstacle). The prerequisite for this is that the flow goes beyond the ridge line at a low altitude or simple ignorance of the theory. Flying in a rotor is fraught with, at a minimum, an unpleasant bump, and at a maximum, a somersault and destruction of the apparatus.

The second striking incident is being pulled into a cloud. The prerequisite for this is the processing of TVP near the edge of the cloud, coupled with absent-mindedness, excessive courage or ignorance of the flight characteristics of one’s aircraft. Leading to loss of visibility and orientation in space, in the worst case – to somersault and being thrown to a height unsuitable for life.

Finally, the third classic accident is “twisting” and falling onto a slope or the ground while planting on a hot day. The prerequisite is to fly with the stick thrown, i.e. without reserve speed for maneuver.