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Cloud (natural and man-made)

Clouds are products of condensation of water vapor suspended in the atmosphere, visible in the sky from the earth's surface. They consist of tiny drops of water and / or ice crystals (called cloud elements).

  • droplet cloud elements are observed when the air temperature in the cloud is above -10 °C
  • mixed composition (drops and crystals) - from -10 to -15 °C 
  • crystal – when the temperature in the cloud is below -15 °C

When cloud elements become larger and their rate of fall increases, they fall out of the clouds as precipitation. As a rule, precipitation falls from clouds that at least in some layer have a mixed composition (cumulonimbus, layered-rain, high-layered). Light drizzling precipitation (in the form of drizzle, snow grains, or light fine snow) can fall from clouds of uniform composition (drop or crystal) – layered, layered-Cumulus.


Reduction Height
Silver   About 85 km
Polar stratospheric   20-30 km
Pearl   About 20-30 km
Lenticular (lenticular)   15-20 km
Pyrocumulus   Up to 12 km
  Upper-tier clouds  

Ci 6-12 km

Cc 8-11 km
Pinnately layered

Cs 8-11 km
  Mid-tier clouds  

Ac 3-6 km
Highly layered

As 3-5 km
  Lower-tier clouds  

Ns Up to 3 km

Sc 0.7-2 km
Videobritney Sc mam 0.7-2 km

St Up to 1 km

Cu From 0.3 to 1.5 km


The bottom is from 0.5 to 1.5 km.

The cloud can extend up to 12-13 km

Morning Gloria   100-200 m

Man-made clouds


Cirrus tractus

Ci trac 10 000 to 0 m



For each type of cloud, you can specify in which tier or tiers these clouds occur. Depending on the temperature conditions and the height of the tropopause, the boundaries of the tiers differ slightly in different latitudes. 

The base of the clouds:

  • the upper tier is located in polar latitudes at altitudes from 3 to 8 km, in temperate latitudes-from 6 to 13 and in tropical latitudes - from 6 to 18 km;
  • middle tier – from 2 to 4, from 2 to 7 and from 2 to 8 km, respectively;
  • lower tier at all latitudes-from the earth's surface to 2 km. 

Cirrus, Cirrus-Cumulus, and Cirrus-layered clouds occur in the upper tier

High-beam and high-layered - in the middle tier

Stratified-Cumulus, stratified and stratified-rain - in the lower

Highly layered clouds often penetrate the upper tier,while layered rain clouds usually penetrate the overlying tiers as well.

The bases of cumulonimbus and cumulonimbus clouds are almost always located in the lower tier, but their tops often penetrate into the middle, and in cumulonimbus clouds into the upper tier. Therefore, these clouds are called vertical development clouds, as well as convective clouds.

There are quite a lot of cloud forms, but in the modern version of the international classification, clouds are divided into ten main forms (genera) by appearance. In the main genera, a significant number of species,varieties, and additional features are distinguished, and intermediate forms are also distinguished.

We should also highlight this type of cloud as man-made or artificial clouds-Ci trac. (Cirrus tractus, cirrus-feathery, tractus —trace).

A condensation trail (misnamed: obsolete-inversion trail, slang-jet trail) is a visible trail of condensed water vapor that occurs in the atmosphere behind moving aircraft under certain atmospheric conditions. The phenomenon is observed most often in the upper layers of the troposphere, much less often in the tropopause and stratosphere. In some cases, it can be observed at low altitudes.

The trace gets its name from the condensation process that leads to its appearance. It occurs only under such conditions when the amount of water vapor exceeds the amount necessary for saturation. These conditions are determined by the dew point-the temperature at which water vapor contained in the air reaches saturation at a given specific humidity and constant pressure. The degree of saturation is characterized by relative humidity – the percentage of the amount of water vapor contained in the air to the amount required for saturation (at the same temperature).

In addition to these conditions, it is also necessary to have condensation centers. At temperatures up to -30... -40 °C, water vapor passes into the liquid phase during condensation, and at temperatures below -30... -40 °C, water vapor immediately turns into ice crystals, bypassing the liquid phase.

Evaporation also plays an important role in the formation of the trace, which leads to its disappearance.

There are two main reasons for the conditions for condensation and the appearance of a trace:

1. Increase in air humiditywhen water vapor contained in the exhaust gases of an aircraft engine is added to atmospheric water vapor as a result of fuel combustion. This increases the dew point in the limited volume of air (behind the engines). If the dew point becomes higher than the ambient temperature, the excess water vapor condenses as the exhaust gas cools. The amount of water vapor emitted by the engine depends on its power and operating mode, i.e. on fuel consumption.

2. Lowering the pressure and temperature of the air above the wing and inside the vorticesthat occur when various parts of the aircraft flow around. The most intense vortices are formed at the wing tips and flaps released, as well as at the ends of the propeller blades. If the temperature falls below the dew point, excess atmospheric water vapor condenses in the area above the wing and inside the vortices. The degree of pressure and temperature reduction depends on such parameters as the mass of the aircraft, the lift coefficient, the value of inductive resistance, etc. Often there are traces formed as a result of a combination of these two causes. Condensation trace formation is also facilitated by condensation centers in the form of particles of unburned or not completely burned (soot) fuel.

Along with condensation, the reverse process occurs - evaporation: particles of condensed water vapor evaporate, and the trace disappears over time. The evaporation rate is affected by the humidity of the surrounding air and the aggregate state of the trace particles. The drier the air, the faster evaporation occurs. On the contrary, evaporation does not occur when the water vapor is saturated. Condensed water vapor at an air temperature of−30... -40 °C partially, and at a temperature below -40 °C completely turns into crystals, the evaporation of ice crystals is much slower than water droplets.

Thus, the possibility of occurrence and lifetime of the condensation trace, as well as its type, depend on the humidity and temperature of the atmospheric air (other things being equal). At low humidity and relatively high temperature, there may be no trace at all, since under such conditions the water vapor does not reach a state of supersaturation. The higher the humidity and lower the temperature, the more water vapor condenses, the worse evaporation occurs, and therefore the trail is richer and longer. And at a relative humidity close to 100 % and a low temperature, the largest amount of water vapor condenses, high humidity prevents the evaporation of trace particles, which leads to the formation of condensation traces that can exist for a long time, often turning into Cirrus or Cirrus-Cumulus clouds. Since water vapor in the atmosphere is not evenly distributed, this is the reason for the same" uneven " trace.

Condensation traces are formed not only at high altitudes. At the ice airfield of the Polar Station "Scott Amundsen "(altitude 2830 m above sea level), under certain conditions (air temperature minus 50 degrees and below), this trail is formed already on takeoff or landing, and for turboprop aircraft (C-130" Hercules "from the" Snow Wing " of the US air force).

On the appearance of the so-called "jellyfish" from the launch vehicle occurs in the tropopause. This is affected by water vapor, which is subjected to increased condensation. Thus, these are also condensation traces, but of a slightly different type.

Causes of uneven condensation traces

The uneven distribution of water vapor in the atmosphere causes the same" uneven " trace. You can give several examples of the reasons for uneven tracks:

Wing tip vortex

A flying plane leaves behind a disturbed region of the atmosphere called a satellite trail. This trace is formed mainly by jet jets of engines and end vortices from the wing. Twisting is explained by the difference in pressure on the lower and upper surfaces of the wing. As a result of the flow of air from the area of high pressure on the lower surface of the wing to the area of low pressure on the upper surface, powerful vortices are formed through its end. The greater the pressure drop and, consequently, the lift force with which the flow acts on the wing, the greater the intensity of the end vortices. Circumferential speeds in a vortex track with a diameter of 8-15 m can reach 150 km/h.

The end vortex was visualized using a smoke trace tracer generator. Atmospheric disturbances caused by the influence of the vortex trace exist for a long time, gradually fading, reducing the circumferential speed of movement.

As a result of interaction between each other, the vortices gradually descend and diverge.

Observing the condensation trail of a passing plane, we find that about 30-40 seconds after the plane passes, it begins to change its appearance under the influence of the developing vortex trail. At the intersection of the condensation and vortex traces, very intricate shapes arise that have quite definite patterns.

Number of aircraft engines

Depending on the number of engines and their location on the aircraft, the condensation trail can be one-or two-lane. The condensation trail and its transformation record the aerodynamic processes that accompany the flight of the aircraft.

Torn-off vortex flows

When performing maneuvers at high angles of attack (20° or more), the nature of the flow around the aircraft surfaces changes dramatically. On the upper surface of the wing and fuselage, tear-off areas are formed, in which, due to a decrease in pressure, conditions for condensation of atmospheric moisture arise. Thanks to this, you can watch the flight of the aircraft without tracers.

A bright trace of the fast and the furious

The engines of modern fighter planes are equipped with supersonic adjustable nozzles. As a rule, when the engine is in afterburner mode, the pressure at the nozzle section exceeds the ambient air pressure. At a considerable distance from the nozzle section, the pressure in the jet and in the atmosphere should be equal. As you move away from the nozzle section, the pressure in the jet decreases, and the gas velocity increases. The cross-section of the jet increases, as shown schematically in the figure below.

The gas continues to expand by inertia, and in the widest section of the jet, the pressure becomes lower than atmospheric. After that, the jet begins to narrow, the pressure in it approaches atmospheric, and the speed decreases accordingly. Deceleration of the supersonic flow leads to a direct shock of compaction. As a result, in some parts of the jet, the speeds become subsonic, and the pressure is correspondingly higher than atmospheric. As you can see, the shape of the jet becomes barrel-shaped. Then the process is repeated.

The gas jet has a temperature of more than 2000 °C, so its glow makes visible the processes that occur when it expires. Areas of bright light are visible in those places of the jet where direct jumps of compaction are formed.

When the engine is running on the afterburner, a visible jet of incandescent gases appears behind the jet nozzle, which has a characteristic "striped" structure, the so-called Mach disks).

In case of incomplete combustion of kerosene (due to lack of oxygen), the jet will have a red color with yellow vertical rings. If Gorenje is well optimized, the flame color will be blue. Due to the imperfection of the fuel equipment of some engines, an interesting effect is sometimes observed — on the same aircraft, one engine has a blue exhaust on the afterburner, and the second engine has a red or yellow exhaust.


To fly over the city, there are restrictions on the minimum height, so as not to disturb the residents with engine noise, so the plane over the city increases the height, which can cause the formation of a trace on this section of the trajectory.

Gradually, the balance between the surrounding air and water in the trail will begin to recover, and the trail will melt. The duration of this process depends on many factors. For example, from the content of water and particles of burnt fuel in the exhaust jet, which help to form fog, trapping moisture on themselves. Therefore, traces of different aircraft can melt in different ways – due to differences in fuel composition, engine design and configuration, differences in power and operating modes.

At night, the tracks are thicker and last longer - because at night the atmosphere is more stable and the condensate cloud is not heated by the sun. Which keeps its temperature within the dew point. 

Bizarre forms of man-made clouds

Depending on the environmental conditions (for example, air flow) and the characteristics of the aircraft, they can take bizarre forms.

Sometimes you can use these footprints to create drawings or even write letters, symbols, words, and entire sentences. This type of email is called Skywriting. The first inscriptions in the sky were made in England in 1919, in America-in 1920. Now labels can be of various colors and sizes and are applied mainly for advertising purposes.

It is usually white, but it can also be dark in color. A dark trail behind an ordinary aircraft is formed from fuel that is not completely burned out. This usually occurs during transient modes, i.e. during acceleration or maneuvering.

Condensation trail in the form of a loop (circle, sharp u-turn) often leaves the plane, which makes visual monitoring of the weather. In this case, the aircraft rises to 10,000 m, stands in a circle to communicate with alternate airfields, and then descends in a short spiral.

Sometimes condensation (inversion) traces of aircraft can take bizarre shapes and outlines: they appear in various swirls, rings, rounded structures, turrets, threads. Such formations are caused by an action instability crow (Crow Instability) by the name of its discoverer. Most often, this phenomenon is observed for huge liners, when air vortices behind the wings interact with the inversion track and create sinusoidal vibrations, distorting its original structure.


The movement of clouds in different directions can be observed in cases when they are not continuous, they are located at different levels, and the wind at different heights has a different direction.

Clouds in the air move along the air flow, and it changes with height sometimes not very noticeably, and sometimes - by a very significant angle, easily fixed visually, without any devices. The reasons for the change of direction, and wind speed with the height of several: thus in the lower layer is to reduce friction of air flow on the earth's surface (wind with height by weakening friction increases and gradually turns to the right by several tens of degrees, usually not more than 30-40°); at higher levels it is influenced by the horizontal temperature distribution experiences a left or right rotation, increases or decreases, may even change in the opposite direction. Meteorologists know that with altitude, when transferring heat, the wind gradually turns to the right, when transferring cold-to the left. In General, it always obeys a simple law: it blows along lines of equal pressure-the Isobar, leaving a low-pressure area on the left. The position of the isobars with height changes in accordance with the horizontal distribution of air temperature.

Due to friction with the earth's surface, the wind speed at the ground is less than at altitudes. The layer of air in which the speed deceleration occurs is called the deceleration layer. On flat terrain, the height of the braking layer is 1-2 km. The higher the speed, the stronger the effect of the Coriolis force, therefore, as the height increases in the braking layer, a right turn occurs in the Northern hemisphere and a left turn in the southern hemisphere.

In the braking layer, the wind speed increases with increasing altitude, and its direction in the Northern hemisphere turns to the right.

The wind is calm only at low speeds (up to 4 m/s) — air particles move along parallel trajectories. At a speed of more than 4 m / s, the air flow becomes swirling (turbulent) in nature, in which the paths of individual air jets intersect and become very complex.

There is a stable pattern of decreasing wind speed with altitude and changing the wind direction to the opposite in the stratosphere during the warm season. This wind reversal occurs at an altitude of about 20 km. In fact, the transition of the wind from the West to the East, that is, the opposite direction, occurs in a layer several hundred meters thick. This layer is called the velopause. The change in wind direction is associated with the formation of a high-altitude anticyclone in the stratosphere in summer, which replaces the winter cold circumpolar cyclone during the polar day. As soon as at altitudes the direction in which the pressure decreases changes along the horizon to the opposite, the wind direction changes in the same way.

Meteorological wind data specified in the weather forecast on thematic sites or in the media is determined by averaging over a 10-minute period of time the anemometer readings located at a 10-meter height. These measurements can be repeated every hour.


Thus, the clouds themselves, due to the variety of shapes, can be mistaken for UFOs, but they can also serve as assistants for calculating the approximate height of the UFO flight. To do this, you need to know the classification of clouds and the processes occurring in the troposphere.

Using this data, you can not only calculate (or simply estimate) the height of an object flying in the sky and its speed, but also distinguish between objects moving due to the wind and independently of it.

First of all, when you notice an object flying in the sky, you need to pay attention to the presence of clouds. By their appearance, you can determine the type. This will allow you to estimate the approximate altitude of the cloud. After finding out whether the object is hidden behind a cloud, or is located below it, you can mark the approximate height of the object's flight.

In addition, the above data allows you to approximate the speed of the object.

The object can move in the direction of cloud movement, against, and have an independent flight path. You can estimate the type of movement of an object by comparing the trajectory and speed of the object and the clouds at the height of the object's movement (since the wind speed and direction may differ at different heights).

You can calculate the relative speed of an object by measuring the time of movement of a cloud or part of it relative to stationary objects (for example, between two branches of a tree) and the time it takes for the observed object to travel the same distance.

If you can determine that the object is flying at a low altitude (less than 1 km), you should pay attention to the smoke if there are pipes in the visibility zone (for example, factory pipes). The height at which the smoke stops rising indicates a temperature inversion and possible wind shear. Horizontal smoke from the pipe indicates a wind speed exceeding 6...8 m/s. The angle of deviation of the smoke from the vertical indicates its strength – the greater the angle, the greater the wind force.

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