Clouds Form If Air Is

CLOUDS - HOW Practise THEY FORM?

Wind is the horizontal movement of air, transporting energy transferred from the world's surface as sensible and latent heat. Sensible heat is transferred by the processes of conduction and convection. Conduction transfers free energy inside a substance, and convection transfers energy through the vertical movement of the heated substance. Latent heat is the transfer of free energy by transforming the substance itself. As you recall, h2o has the ability to exist every bit liquid, gas or solid. The transformation from liquid to gas is called evaporation; the reverse process, from gas to liquid, is called condensation; from liquid to solid is known as solidification (freezing); and from solid to liquid, fusion (melting). Water tin can also be transformed directly from solid to gas (sublimation), or the reverse, through a procedure chosen degradation. We will encounter these various processes in the formation of clouds.

Clouds are formed when air contains every bit much water vapor (gas) equally it can concord. This is called the saturation bespeak, and it tin exist reached in 2 ways. First, moisture accumulates until it reaches the maximum amount the volume of air tin hold. The other method reduces the temperature of the wet filled air, which in turn lowers the corporeality of wet it can contain. Saturation, therefore, is reached through evaporation and condensation, respectively. When saturation occurs, moisture becomes visible water aerosol in the form of fog and clouds.

It should exist noted that condensation by itself does non cause precipitation (pelting, snow, sleet, hail). The moisture in clouds must become heavy plenty to succumb to gravity and return to earth'southward surface. This occurs through two processes. In cold clouds ice crystals and water droplets exist adjacent. Due to an imbalance of water vapor force per unit area, the h2o droplets transfer to the ice crystals. The crystals eventually grow heavy enough to fall to earth. In the second procedure, water droplets in warm clouds collide and alter their electric accuse. Droplets of different charge attract ane some other and merge, thereby growing until they have sufficient weight to fall.

In that location is no difference between fog and clouds other than altitude. Fog is defined equally a visible moisture that begins at a tiptop lower than 50 feet. If the visible moisture begins at or to a higher place 50 anxiety, it is chosen a cloud. Two common types of fog are chosen radiation fog and advection fog. Radiation fog forms during the night equally the world'due south surface cools and the air immediately above it cools in turn past conduction. If the air is moist plenty, the cooling causes it to reach saturation and visible water droplets form. We frequently call this type of fog ground fog because information technology lies so close to the surface. Advection fog forms when warm moist air moves over a colder surface (advection means to move horizontally). A perfect example is on the west coast of continents. Prevailing westerly winds move moist air from over a warm bounding main area to over the colder waters off the coast. Fog forms and is carried by the westerly over the land.

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Although the germination of clouds and precipitation can be quite complex in full item, we can simplify the process into a elementary recipe, expert for the vast bulk of situations.

Showtime, nosotros demand two basic ingredients: water and dust.

On Planet Earth, naturally occurring clouds are equanimous primarily of water in its liquid or solid state. (On other planets, clouds may form from other compounds such equally the sulphuric acid clouds on Venus.) Thus, nosotros begin our recipe by collecting a sufficient quantity of water in the vapor country that we will soon transform into the liquid or solid states. The h2o vapor content of the atmosphere varies from most zero to about 4 per centum, depending on the moisture on the surface beneath and the air temperature.

Adjacent, we demand some dust. Not a large amount nor large particles and not all dusts will do. Without "muddied air" there would probable be no clouds at all or simply high altitude ice clouds. Even the "cleanest" air institute on Earth contains about 1000 dust particles per cubic meter of air. Dust is needed for condensation nuclei, sites on which water vapor may condense or deposit every bit a liquid or solid. Certain types and shapes of dust and salt particles, such every bit sea salts and dirt, brand the best condensation nuclei.

With proper quantities of h2o vapor and grit in an air parcel, the next step is for the air parcel mass to be cooled to a temperature at which cloud droplets or ice crystals can form. And, voila, nosotros have clouds.

This unproblematic recipe is a lot similar cooking craven -- you have a chicken and some spices, apply heat and subsequently a fourth dimension y'all have a cooked chicken. But only equally there are many ways to cook craven, in that location are many different ways to class clouds.

THE Precipitation LADDER
eleven. Precipitation
ten. DROPLET GROWTH
9. BUOYANCY/CLOUDINESS
8. CONDENSATION
7. SATURATION
6. HUMIDIFICATION
5. COOLING
4. EXPANSION
3. Rise
2. DIRTY AIR
one. Water VAPOR

Let us now expand our recipe and add precipitation. Professor John Day, the Cloud Man, has taken the unproblematic cloud recipe, added a few more details and continued it until it also makes precipitation. He calls this The Atmospheric precipitation Ladder. As with our elementary recipe, he begins the procedure with the bones ingredients of dirty air and water vapor. In Rungs 3 through 8, he takes the ingredients through several processes to form a cloud.

Rise and Expansion are two of the primary processes that result in the cooling of an air parcel in which clouds will form. Nosotros mostly think of moving air as current of air flowing horizontally across the surface. Just air moving vertically is extremely important in weather processes, especially with respect to clouds and precipitation. Ascending air currents take us upwards the Precipitation Ladder. (Where descending currents are present, we come downwardly the Ladder with processes reversing until we are finally left with h2o vapor and dust in an air mass.)

There are four main processes occurring at or nearly the earth's surface which give tin can rising to ascending air: convergence, convection, frontal lifting and physical lifting.

Convergence occurs when several surface air currents in the horizontal menstruation motility toward each other to run into in a common infinite. When they converge, there is only i mode to go: Up. A surface low pressure prison cell is an example of an expanse of convergence and air at its eye must rise equally a upshot.

Convection occurs when air is heated from below by sunlight or by contact with a warmer state or water surface until information technology becomes less dumbo than the air in a higher place it. The heated parcel of air will rise until it has again cooled to the temperature of the surrounding air.

Frontal lifting occurs when a warmer air mass meets a colder one. Since warm air is less dense than cold, a warm air mass budgeted a cold one volition ascend over the common cold air. This forms a warm front. When a cold air mass approaches a warm one, it wedges under the warmer air, lifting it in a higher place the ground. This forms a cold front. In either example, there is ascending air at the frontal purlieus.

Physical lifting, also known every bit orographic lifting, occurs when horizontal winds are forced to ascent in order to cross topographical barriers such as hills and mountains.

Whatever the process causing an air bundle to ascend, the consequence is that the rise air package must change its pressure to exist in equilibrium with the surrounding air. Since atmospheric force per unit area decreases with distance, and then too must the pressure of the ascending air parcel. As air ascends, it expands. And equally it expands, it cools. And the higher the parcel rises, the cooler information technology becomes.

At present that we have begun cooling the air parcel, we are well-nigh gear up to form a cloud. We must continue to cool the bundle until condensation is reached. The next several rungs of the Precipitation Ladder draw the processes through to the condensation of liquid water.

As the air cools, its relative humidity will increment - a process 24-hour interval terms humidification (Rung 6). Although nothing has yet happened to change the h2o vapor content of the air, the saturation threshold of the air parcel has decreased as the air cooled. By decreasing the saturation threshold, the relative humidity increases. Cooling is the most of import method for increasing the relative humidity but it is non the only one. Some other is to add more water vapor through evaporation or mixing with a more humid air mass.

If we are to course a cloud, humidification may somewhen bring the air within the parcel to saturation. At saturation the relative humidity is 100 percent. Ordinarily a little more humidification is required which brings the relative humidity to over 100 per centum, a land known as supersaturation, earlier a cloud will form. When air becomes supersaturated, its water vapor looks for ways to condense out. If the quantity and limerick of the grit content is ideal, condensation may begin at a relative humidity below 100 percent. If the air is very clean, it may accept loftier levels of supersaturation to produce cloud droplets. Only typically condensation begins at relative humidity a few tenths of a percent above saturation.

Condensation of water onto condensation nuclei (or deposition of h2o vapor as water ice on freezing nuclei) begins at a particular altitude known as the cloud base of operations or lifting condensation level. Water molecules adhere to the particles and form cloud droplets which have a radius of about 20 micrometers (0.02 mm) or less. The droplet book is more often than not a million times greater than the typical condensation nuclei.

Clouds are composed of large numbers of cloud droplets, or ice crystals, or both. Considering of their small size and relatively high air resistance, they tin can remain suspended in the air for a long time, particularly if they remain in ascending air currents. The boilerplate cloud droplet has a terminal fall velocity of one.3 cm per second in still air. To put this into perspective, the average cloud droplet falling from a typical low deject base of 500 meters/1,650 feet would take more than 10 hours to reach the footing.

We now know that cirrus clouds in their various forms are composed of ice crystals, and the upper levels of tall cumulus may likewise have ice in them fifty-fifty in the summer.

While clouds in their varied forms and appearances (Run across Cloud Atlas) are a source of much interest, we will get out them at present and go along upward the Precipitation Ladder toward the top rung: Atmospheric precipitation. Forming Precipitation Light Pelting

We know that not all clouds produce rain that strikes the basis. Some may produce rain or snowfall that evaporates before reaching the footing, and nearly clouds produce no precipitation at all. When rain falls, we know from measurements that the drops are larger than ane millimeter. A raindrop of diameter 2 mm contains the water equivalent of a million cloud droplets (0.02 mm bore). So if we are to get some precipitation from a deject, in that location must be boosted procedure within the cloud to form raindrops from cloud aerosol.

The next rung of the Precipitation Ladder is Buoyancy or Cloudiness which signifies that we must increase the cloud water content before we tin can wait any precipitation.

This requires a continuation of the lifting process. It is assisted past the property of water of giving off heat when changing from vapor to liquid and solid states, the latent heats of condensation and of deposition, respectively. (If the vapor first changes to a liquid before freezing, then we also have the latent heat of condensation released and followed by the release of the latent oestrus of freezing.) This additional heat release warms the air parcel. In doing so, the buoyancy of the parcel relative to the surrounding air increases, and this contributes to the parcel's further ascent. We tin encounter the continued ascent of these parcels in cumulus clouds that reach corking vertical growth.

Now in the cloud, there must be Growth of deject droplets to sizes that can fall to the ground equally rain (we will expect at snow in a infinitesimal) without evaporating. Cloud droplets can grow to a larger size in three ways.

The first is by the continued condensation of water vapor into cloud droplets and thus increasing their volume/ size until they get droplets. While the first condensation of water onto condensation nuclei to form cloud droplets occurs rather apace, connected growth of cloud droplets in this style will proceed very slowly.

Second, growth by standoff and coalescence of cloud droplets (and and then the standoff of pelting drops with cloud droplets and other drops) is a much quicker process. Turbulent currents in the clouds provide the first collisions between droplets. The combination forms a larger drop which can further collide with other droplets, thus growing speedily in size.

Equally the drops abound, their fall velocity also increases, and thus they can collide with slower falling droplets. A 0.5 mm-radius drop falling at a rate of 4 g/s can quickly overtake a 0.05 mm (l micrometer) drib falling at 0.27 one thousand/s. When drops are too big, yet, their collection efficiency for the smallest drops and droplets is non as corking as when the drops are nearer in size. Small aerosol may bounce off or flow around much larger drops and therefore do not coagulate. A drop about 60% smaller in bore is almost likely to be nerveless past a large driblet.

Clouds with strong updraft areas have the best drop growth considering the drops and droplets stay in the deject longer and thus take many more collision opportunities.

Finally, it may seem odd, but the best conditions for drop growth occur when ice crystals are nowadays in a cloud. When in small droplet form, liquid water must exist cooled well below 0 ° C (32 °F) before freezing. In fact, under optimal atmospheric condition, a pure droplet may reach -xl °C before freezing. Therefore, there are areas within a cloud were ice crystals and h2o droplets co-be.

When ice crystals and supercooled droplets are most each other, at that place is a movement of water molecules from the droplet to the crystal. This increases the size of the water ice crystal at the expense of the droplet. When the crystals grow at temperatures around -ten °C (14 °F), they begin to develop artillery and branches, the stereotypical snowfall crystal. Such crystals not only are efficient at growing at the expense of water droplets, they likewise easily stick to one another forming big aggregates we call snowflakes.

Finally, the drops have grown to a size that they can fall in a reasonable time to the surface without evaporating, and we accept reached the top rung Precipitation. (For more than on raindrops, click here.)The following table gives some typical drop diameters for various pelting types, using cloud droplets as a reference size. Most rain falls in the range of 0.2 to 5 mm (0.008 to 0.20 inch).

Of course, not all precipitation falls as rain. A fair amount of the world's atmospheric precipitation falls as snow or some other solid water grade. Actually, exterior the tropical regions, it is likely that the much of the atmospheric precipitation begins in the solid form and but becomes liquid rain when information technology melts while falling through air with temperatures higher up freezing.

Most people telephone call nigh any frozen grade of precipitation, other than hail or ice pellets, a snowflake. Simply meteorologists are a scrap more fussy. Technically the term snowflake refers to an assemblage of individual snowfall crystals that have bumped together and remain joined during their fall. Snowflakes typically fall when air temperatures near the earth'southward surface are not far from the freezing mark. Snow crystals adhere to each other improve at these temperatures. At very cold temperatures, snowflakes are uncommon and we run across generally snowfall crystals during a snow fall.

Snow crystals are typically 0.five to five millimeters ( 0.02 to 0.twenty inches) in size whereas snowflakes are about x mm in size (0.four inches) and may be as large as 200 to 400 mm (0.79 to 1.57 inches).

Other common forms of solid precipitation are: hail, sleet or water ice pellets, graupel or soft hail or snow grains, and a special course: freezing rain, also known equally glaze or rime. The latter falls as a liquid just freezes on contact with an object. When clear ice forms, freezing rain is called glaze. When the water ice is milky, it is called rime.

Hail is a miracle of severe thunderstorms, requiring strong updrafts to form hailstones by passing the hailstone seed many times through air laden with drops and ice crystals.

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OUTLINE - CAUSES OF CLOUDINESS

A) Cooling of air to dew betoken

one) Lifting

a) Convection

one) Heating from below

A) Advection over warmer surface

B) Insolation

C) Advection of warm air in the lowest layers

2) Cooling from above

A) Radiation from top of cloud deck

B) Advection of common cold air aloft

b) Mechanical lifting along a surface

1) Orographic

ii) Overrunning forth a potential temperature surface

three) Upglide along a frontal surface

c) Convergence

ane) Low pressure center of trough

two) Wind shear (speed and/or directional convergence)

3) Latitudinal modify (northward moving current)

4) Vorticity increment (southward moving current)

two) Radiation (fog)

three) Conduction from libation surface (fog)

4) Mixing with cooler air mass

B) Increment in moisture (warming dew signal to temperature)

1) Mixing

a) Caused past convection

b) Caused by strong winds

2) Contact with moist surface

3) Evaporation from falling precipitation

A) Formation in other area covered above

B) Changes during advection as indicated above for the various operating processes

Peak

What causes clouds?
What influences the color of clouds?
Why do clouds end growing upward?
Why are at that place no clouds on some days?
Types of clouds
Low clouds
Medium clouds
High clouds
Measuring clouds
The formation of atmospheric precipitation

What causes clouds?

A cloud is defined every bit 'a visible aggregate of infinitesimal droplets of water or particles of ice or a mixture of both floating in the complimentary air'. Each droplet has a diameter of about a hundredth of a millimeter and each cubic meter of air will contain 100 million droplets. Because the droplets are so small, they can remain in liquid course in temperatures of -thirty °C. If so, they are called supercooled droplets.

Clouds at higher and extremely cold levels in the temper are composed of ice crystals - these tin can be about a tenth of a millimeter long.

Clouds form when the invisible water vapor in the air condenses into visible h2o droplets or water ice crystals. For this to happen, the parcel of air must be saturated, i.due east. unable to hold all the h2o it contains in vapor form, so it starts to condense into a liquid or solid form. In that location are 2 ways past which saturation is reached.

(a) Past increasing the water content in the air, e.1000. through evaporation, to a betoken where the air can hold no more.

(b) By cooling the air and then that it reaches its dew bespeak - this is the temperature at which condensation occurs, and is unable to 'concur' any more water. Figure i shows how in that location is a maximum amount of water vapor the air, at a given temperature, can concur. In general, the warmer the air, the more water vapor it tin hold. Therefore, reducing its temperature decreases its ability to hold h2o vapor and then that condensation occurs.

Method (b) is the usual style that clouds are produced, and information technology is associated with air rising in the lower part of the atmosphere. Equally the air rises information technology expands due to lower atmospheric pressure, and the energy used in expansion causes the air to absurd. By and large speaking, for each 100 meters/330 feet which the air rises, it will cool past ane °C, as shown in Figure 2 . The rate of cooling will vary depending on the water content, or humidity, of the air. Moist parcels of air may cool more than slowly, at a rate of 0.5 ° C per 100 meters/330 feet.

Therefore, the vertical rise of air will reduce its power to agree h2o vapor, and then that condensation occurs. The height at which dew point is reached and clouds form is called the condensation level.

There are v factors which can lead to air rise and cooling:

1. Surface heating. The ground is heated by the sunday which heats the air in contact with information technology causing it to ascension. The ascent columns are oft called thermals.
ii. Topography. Air forced to rise over a bulwark of mountains or hills. This is known every bit orographic uplift.
3. Frontal. A mass of warm air rising upward over a mass of cold, dense air. The boundary is called a 'front'.
4. Convergence. Streams of air flowing from different directions are forced to rising where they run across.
five. Turbulence. A sudden change in wind speed with height creating turbulent eddies in the air.

Another important gene to consider is that water vapor needs something to condense onto. Floating in the air are millions of minute salt, dust and fume particles known as condensation nuclei which enable condensation to take place when the air is just saturated.

What influences the color of clouds?

Low-cal from both the heaven and from clouds is sunlight which has been scattered. In the case of the sky, the molecules of air (nitrogen and oxygen) undertake the scattering, but the molecules are so small that the blue office of the spectrum is scattered more strongly than other colors.

The water aerosol in the cloud are much larger, and these larger particles scatter all of the colors of the spectrum by about the same amount, and so white light from the sun emerges from the clouds even so white.

Sometimes, clouds have a yellowish or brownish tinge - this is a sign of air pollution.

Why do clouds stop growing upward?

Condensation involves the release of latent oestrus. This is the 'invisible' rut which a water droplet 'stores' when it changes from a liquid into a vapor. Its subsequent change of grade again releases enough latent rut to make the damp parcel of air warmer than the air surrounding information technology. This allows the parcel of air to rise until all of the 'surplus' water vapor has condensed and all the latent heat has been released.

Therefore, the primary reason which stops clouds growing upwards is the cease of the release of latent heat through the condensation process. There are two other factors which as well play a office. Faster upper atmospheric winds can plane off the tops of tall clouds, whilst in very high clouds, the cloud might cross the tropopause, and enter the stratosphere where temperatures rise, rather than decrease, with altitude. This thermal change will preclude further condensation.

Why are in that location no clouds on some days?

Even when information technology is very warm and sunny, there might non be any clouds and the heaven is a articulate bluish. The usual reason for the absence of clouds volition be the type of pressure level, with the expanse existence under the influence of a high pressure or anticyclone. Air would exist sinking slowly, rather than ascent and cooling. As the air sinks into the lower part of the atmosphere, the force per unit area rises, it becomes compressed and warms upward, so that no condensation takes place. In simple terms, there are no mechanisms for clouds to class nether these force per unit area conditions.

Types of clouds

In 1803 a retail pharmacist and amateur meteorologist called Luke Howard proposed a system which has afterwards go the basis of the nowadays international classification. Howard also become known by some people as "the father of British meteorology", and his pioneering piece of work stemmed from his marvel into the vivid sunsets in the tardily 18th century post-obit a series of violent volcanic eruptions. They had ejected dust high up into the atmosphere, thereby increasing the amount of condensation nuclei, and producing spectacular deject formations and sunsets.

Howard recognised four types of cloud and gave them the following Latin names:

Cumulus - heaped or in a pile
Stratus - in a sheet or layer
Cirrus - thread-similar, hairy or curled
Nimbus - a rain bearer

If we include another Latin word altum pregnant peak, the names of the ten main cloud types are all derived from these five words and based upon their advent from footing level and visual characteristics.

The cloud types are carve up into iii groups according to the tiptop of their base higher up mean sea level. Note that 'medium' level clouds are prefixed past the discussion alto and 'high' clouds by the word cirro (see Table 1). All heights given are judge to a higher place ocean level in mid-latitudes. If observing from a hill top or mountain site, the range of bases will accordingly be lower.

Low clouds Surface - 7,000 ft
Medium clouds 7,000 - 17,000 ft
Loftier clouds 17,000 - 35,000 ft

LOW CLOUDS

Cumulus (Cu)
Height of base: 1,200-6,000 ft
Colour: White on its sunlit parts but with darker undersides.
Shape: This cloud appears in the form of detached heaps. Shallow cumulus may announced quite ragged, especially in stiff winds, but well formed clouds have flattened bases and sharp outlines. Big cumulus clouds take a distinctive "cauliflower" shape.
Other features: Well adult cumulus may produce showers.

Cumulonimbus (Cb)
Elevation of base: 1,000-v,000 ft
Color: White upper parts with dark, threatening undersides.
Shape: A cumulus-type deject of considerable vertical extent. When the top of a cumulus reaches great heights, the water aerosol are transformed into ice crystals and information technology loses its clear, sharp outline. At this phase the cloud has become a cumulonimbus. Often, the gristly cloud height spreads out into a distinctive wedge or anvil shape.
Other features: Accompanied by heavy showers, perhaps with hail and thunder. By convention Cb is usually reported if hail or thunder occur, even if the observer does not immediately recognise the cloud as Cb; (it may be embedded within layers of other cloud types).

Stratus (St)
Height of base of operations: surface-1,500 ft
Color: Normally grey.
Shape: May announced every bit a layer with a fairly uniform base or in ragged patches, especially during precipitation falling from a cloud layer above. Fog will oftentimes lift into a layer of stratus due to an increase in wind or rising in temperature. Every bit the sun heats the ground the base of stratus cloud may rise and break becoming shallow cumulus cloud every bit its edges take on a more distinctive grade.
Other features: If thin, the disc of the sunday or moon will exist visible (providing there are no other cloud layers in a higher place). If thick, it may produce drizzle or snow grains.

Stratocumulus (Sc)
Height of base of operations: 1,200-7,000 ft
Colour: Grey or white, by and large with shading.
Shape: Either patches or a sail of rounded elements merely may as well appear as an undulating layer. When viewed from the basis, the size of individual elements volition have an apparent width of more than 5degree when at an elevation greater than 30degree (the width of three fingers at arm's length).
Other features: May produce low-cal rain or snow. Sometimes the cloud may consequence from the spreading out of cumulus, giving a light shower.

MEDIUM CLOUDS

Altocumulus (Ac)
Height of base: 7,000-17,000 ft
Colour: Grey or white, generally with some shading.
Shape: Several unlike types, the most common being either patches or a sheet of rounded elements only may also announced as a layer without much form. When viewed from the ground, the size of individual elements will have an credible width of one to 5degree when at an elevation greater than 30degree (the width of 1 to three fingers at arm'south length). Even if the elements appear smaller than this the deject is withal classified altocumulus if it shows shading.
Other features: Occasionally some slight pelting or snow, perhaps in the grade of a shower may accomplish the ground. On rare occasions, a thunderstorm may occur from one type of Ac known equally altocumulus castellanus — so chosen because in outline, the cloud tops look similar a series of turrets and towers forth a castle wall.

Altostratus (As)
Height of base: 8,000-17,000 ft
Color: Greyish or bluish.
Shape: A canvass of compatible appearance totally or partly covering the sky.
Other features: Sometimes sparse enough to reveal the lord's day or moon vaguely, as through ground drinking glass. Objects on the basis do not cast shadows. May requite by and large light rain or snow, occasionally ice pellets, if the cloud base is no college than about ten,000 ft.

Nimbostratus (Ns)
Peak of base of operations: 1,500-10,000 ft
Color: Dark grey.
Shape: A thick, lengthened layer covering all or most of the heaven. Other features: Sun or moon e'er blotted out. Accompanied by moderate or heavy rain or snow, occasionally water ice pellets. Although classed as a medium cloud, its base frequently descends to low cloud levels. May be partly or even totally obscured by stratus forming underneath in precipitation.

Loftier CLOUDS

Cirrus (Ci)
Height of base of operations: 17,000-35,000 ft
Colour: Composed of water ice crystals, therefore white.
Shape: Fragile pilus-like filaments, sometimes hooked at the terminate; or in denser, entangled patches; or occasionally in parallel bands which announced to converge towards the horizon. Other features: The remains of the upper portion of a cumulonimbus is besides classified as cirrus.

Cirrocumulus (Cc) Pinnacle of base of operations: 17,000-35,000 ft
Color: Composed of ice crystals, therefore white.
Shape: Patches or sheet of very small elements in the class of grains or ripples or a honeycomb. When viewed from the ground, the size of individual elements will take an apparent width of less than 1degree when at an elevation greater than 30degree (no greater than the width of a piddling finger at arm'southward length).
Other features: Sometimes its appearance in a regular pattern of 'waves' and small gaps may resemble the scales of a fish, thus giving rising to the pop name 'mackerel sky'. (this name may also be attributed to high altocumulus clouds).

Cirrostratus (Cs) Peak of base: 17,000-35,000 ft
Color: Equanimous of ice crystals, therefore white.
Shape: A transparent veil of gristly or polish appearance totally or partly covering the heaven.
Other features: Thin enough to allow the sun to bandage shadows on the ground unless it is depression in the sky. Produces halo phenomena, the near frequent being the small (22degree ) halo around the sun or moon — a little more than the distance between the top of the pollex and the pinkie spread broad apart at arm's length.

Condensation trails (contrails)
These are thin trails of condensation, formed by the h2o vapor rushing out from the engines of jet aircraft flying at high altitudes. They are not true clouds, only tin can remain in the sky for a long time, and abound into cirrus clouds.

Measuring clouds

The cloud amount is defined as 'the proportion of the celestial dome which is covered by deject. The scale used is eighths, or oktas, with observers standing in an open infinite or on a rooftop to get a good view or panorama of the sky.

Complete deject cover is reported as 8 oktas, half cover equally 4 oktas, and a completely clear sky as zero oktas. If there is low-lying mist or fog, the observer will study sky obscured.

The reporter will also report the amount of each cloud level — 2 oktas of cumulus and iii oktas of cirrus, etc.

The frequent passage of depressions across the U.k. means that the most commonly reported cloud amount is, not surprisingly, viii oktas. A clear blue sky, i.e. zero oktas, is less mutual, equally often on hot, sunny days, in that location are small wispy layers of cirrostratus or fine tufts of sparse cirrus at loftier altitudes.

The formation of precipitation

Cooling, condensation and cloud formation is the start of the procedure which results in atmospheric precipitation. Only non all clouds volition produce raindrops or snowflakes — many are then brusque-lived and minor that there are no opportunities for precipitation mechanisms to commencement.

There are ii theories that explain how minute cloud aerosol develop into precipitation.

1. The Bergeron-Findeisen water ice-crystal mechanism

If parcels of air are uplifted to a sufficient top in the troposphere, the dew betoken temperature will be very low, and minute ice crystals volition kickoff to form. The supercooled water droplets will also freeze on contact with these water ice nuclei.

The water ice crystals subsequently combine to form larger flakes which attract more supercooled droplets. This process continues until the flakes fall dorsum towards the ground. As they fall through the warmer layers of air, the ice particles melt to class raindrops. However, some water ice pellets or snowflakes might exist carried down to ground level past cold downdraughts.

2. Longmuir's collision and coalescence theory

This applies to 'warm' clouds i.e. those without large numbers of water ice crystals. Instead they incorporate water aerosol of many differing sizes, which are swept upwards at unlike velocities and then that they collide and combine with other droplets.

It is idea that when the droplets have a radius of 3 mm, their movement causes them to splinter and disintegrate, forming a fresh supply of h2o droplets.

Human being-made rain

In recent years, experiments have taken place, chiefly in the The states and the former USSR, adding particles into clouds that act as condensation or freezing nuclei. This cloud seeding involves the addition into the atmosphere from shipping of dry water ice, silver iodide or other hygroscopic substances. These experiments have largely taken place on the margins of farming areas where rainfall is needed for crop growth.

Tiptop

Clouds can form anywhere in the troposphere, and although condensed liquid, they are calorie-free enough to bladder in the air and move from place to place by the wind. Clouds are classified according to appearance and height. Based on appearance, there are two major types: Clouds of vertical development, formed by the condensation of rising air; and clouds that are layered, formed by condensation of air without vertical movement. When clouds are classified by height, there are four classes: loftier, center, low, and vertical evolution.

Cloud names, of which there are twelve, combine appearance and superlative. A cursory description of the root proper noun will point this combination of features.

Stratus, strato....Layered or sheetlike
Cumulus, cumulo....Puffy, heaped (vertical)
Nimbus, nimbo......Dark and rainy
Cirrus, cirro......Curly, featherlike (loftier cloud)
Alto...............High (just used to describe a middle deject)
Fracto.............Broken

Let's describe a few familiar cloud formations. The contrary of fog, in terms of altitude, are cirrus clouds. These clouds develop at an average peak of twenty,000 feet. Cirrus clouds look like a person'due south hair, or feathers blowing in the air current. At this altitude, the air is and then common cold that the cloud is composed of ice crystals rather than h2o droplets found at lower altitudes. The strong wind at this loftier altitude blow the clouds in long streamers across the sky.

Another cloud that is formed looks like sheets across the sky. These are stratus clouds. Stratus clouds form when condensation happens at the same level at which the air stops rising. Nosotros notice this on days when the stratus clouds are spread across the sky and it becomes overcast. The skies may have these stratus clouds for days and it also brings rain.

Cumulus clouds are the clouds that seem to make pictures in the heaven. One can make many shapes and designs by watching the clouds pass by overhead. These clouds have a flat bottom and a bouncing top. The base of the cloud forms at the altitude at which the rising air cools and condensation starts. However, rising air remains warmer than the surrounding air and continues to rise. As it rises, more than vapor condenses, forming the billowing columns.

The remaining clouds have been named past combining terms. For example, clouds that are sheet-similar yet accept vertical construction are chosen stratocumulus. The table beneath shows all 12 cloud names. While most rain clouds are in the low cloud range, because most wet is nearer to the earth's surface, special mention should be made of those clouds in the vertical development category. We mentioned before hurricanes and tornadoes earlier. These thunderstorms arise from cumulonimbus clouds, which tin can attain heights of 65,000 feet and builds through all the layers. When the cloud reaches the peak of the troposphere it is well-nigh lopped off by the lid which the stratosphere creates, and the cumulonimbus cloud resembles a behemothic anvil.