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The Short Answer: Clouds are created when water vapor, an invisible gas, turns into liquid water droplets. These water droplets form on tiny particles, like dust, that are floating in the air. A camera on NASA’s Terra satellite captured this image of clouds over the Southern Indian Ocean. Image credit: NASA/JPL-Caltech You hang up a wet towel and, when you come back, it’s dry. You set out a bowl of water for your dog and when you look again, the water level in the bowl has dropped even though Woofy has been nowhere near the bowl.

• Where did the missing water go? It evaporated.
• That means some of the liquid water in the towel or bowl changed into an invisible gas called water vapor and drifted away into the atmosphere.
• Notice that “evaporated” contains the word “vapor.”) The same thing is constantly happening with oceans, lakes, rivers, swamps, swimming pools – and everywhere water is in contact with air.

Liquid water changes into a gas when water molecules get extra energy from a heat source such as the Sun or from other water molecules running into them. These energetic molecules then escape from the liquid water in the form of gas. In the process of changing from liquid to gas, the molecules absorb heat, which they carry with them into the atmosphere. Heat causes some of the liquid water – from places like oceans, rivers and swimming pools – to change into an invisible gas called water vapor. This process is called evaporation and it’s the start of how clouds are formed. Image credit: NASA/JPL-Caltech/Alex Novati The air can only hold a certain amount of water vapor, depending on the temperature and weight of the air – or atmospheric pressure – in a given area.

1. The higher the temperature or atmospheric pressure, the more water vapor the air can hold.
2. When a certain volume of air is holding all the water vapor it can hold, it is said to be “saturated.” What happens if a saturated volume of air cools or the atmospheric pressure drops? The air is no longer able to hold all that water vapor.

The excess amount changes from a gas into a liquid or solid (ice). The process of water changing from a gas to a liquid is called “condensation,” and when gas changes directly into a solid, it is called “deposition.” These two processes are how clouds form. Dust and other particles floating in the air provide surfaces for water vapor to turn into water drops or ice crystals. The tiny drops of water condense on the particles to form cloud droplets. Clouds are made up of a bunch of cloud droplets bundled together with raindrops. Fog can be seen at the top of this image of the 525-foot tall Vehicle Assembly Building at NASA’s Kennedy Space Center in Florida. Image credit: NASA/Ben Smegelsky Although the basic idea of cloud formation is easy to understand, there is much more to learn. NASA has a fleet of spacecraft that orbit Earth, called satellites. Many of them study clouds, weather, climate and more. Image credit: NASA/JPL-Caltech/Alex Novati The better we can understand clouds and the atmosphere that creates them, the better we can find out what’s happening to our climate.

How are clouds formed in simple words?

Although the formation of clouds and precipitation can be quite complex in full detail, we can simplify the process into a simple recipe, good for the vast majority of situations. First, we need two basic ingredients: water and dust. On Planet Earth, naturally occurring clouds are composed primarily of water in its liquid or solid state. (On other planets, clouds may form from other compounds such as the sulphuric acid clouds on Venus.) Thus, we begin our recipe by collecting a sufficient quantity of water in the vapor state that we will soon transform into the liquid or solid states. The water vapor content of the atmosphere varies from near zero to about 4 percent, depending on the moisture on the surface beneath and the air temperature. Next, we need some dust. Not a large amount nor large particles and not all dusts will do. Without “dirty air” there would likely be no clouds at all or only high altitude ice clouds. Even the “cleanest” air found 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 as a liquid or solid. Certain types and shapes of dust and salt particles, such as sea salts and clay, make the best condensation nuclei. With proper quantities of water vapor and dust 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, we have clouds. This simple recipe is a lot like cooking chicken – you take a chicken and some spices, apply heat and after a time you have a cooked chicken. But just as there are many ways to cook chicken, there are many different ways to form clouds. THE PRECIPITATION LADDER 11. PRECIPITATION 10. DROPLET GROWTH 9. BUOYANCY/CLOUDINESS 8. CONDENSATION 7. SATURATION 6. HUMIDIFICATION 5. COOLING 4. EXPANSION 3. ASCENT 2. DIRTY AIR 1. WATER VAPOR Let us now expand our recipe and add precipitation. Professor John Day, the Cloud Man, has taken the simple cloud recipe, added a few more details and continued it until it also makes precipitation. He calls this The Precipitation Ladder. As with our simple recipe, he begins the process with the basic ingredients of dirty air and water vapor. In Rungs 3 through 8, he takes the ingredients through several processes to form a cloud. Ascent and Expansion are two of the main processes that result in the cooling of an air parcel in which clouds will form. We mostly think of moving air as wind flowing horizontally across the surface. But air moving vertically is extremely important in weather processes, particularly with respect to clouds and precipitation. Ascending air currents take us up the Precipitation Ladder. (Where descending currents are present, we come down the Ladder with processes reversing until we are finally left with water vapor and dust in an air mass.) There are four main processes occurring at or near the earth’s surface which give can rise to ascending air: convergence, convection, frontal lifting and physical lifting. Convergence occurs when several surface air currents in the horizontal flow move toward each other to meet in a common space. When they converge, there is only one way to go: Up. A surface low pressure cell is an example of an area of convergence and air at its center must rise as a result. Convection occurs when air is heated from below by sunlight or by contact with a warmer land or water surface until it becomes less dense than the air above 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 approaching a cold one will ascend over the cold air. This forms a warm front. When a cold air mass approaches a warm one, it wedges under the warmer air, lifting it above the ground. This forms a cold front. In either case, there is ascending air at the frontal boundary. Physical lifting, also known as orographic lifting, occurs when horizontal winds are forced to rise in order to cross topographical barriers such as hills and mountains. Whatever the process causing an air parcel to ascend, the result is that the rising air parcel must change its pressure to be in equilibrium with the surrounding air. Since atmospheric pressure decreases with altitude, so too must the pressure of the ascending air parcel. As air ascends, it expands. And as it expands, it cools. And the higher the parcel rises, the cooler it becomes. Now that we have begun cooling the air parcel, we are almost ready to form a cloud. We must continue to cool the parcel until condensation is reached. The next several rungs of the Precipitation Ladder describe the processes through to the condensation of liquid water. As the air cools, its relative humidity will increase – a process Day terms humidification (Rung 6). Although nothing has yet happened to change the water 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 important method for increasing the relative humidity but it is not the only one. Another is to add more water vapor through evaporation or mixing with a more humid air mass. If we are to form a cloud, humidification may eventually bring the air within the parcel to saturation. At saturation the relative humidity is 100 percent. Usually a little more humidification is required which brings the relative humidity to over 100 percent, a state known as supersaturation, before a cloud will form. When air becomes supersaturated, its water vapor looks for ways to condense out. If the quantity and composition of the dust content is ideal, condensation may begin at a relative humidity below 100 percent. If the air is very clean, it may take high levels of supersaturation to produce cloud droplets. But typically condensation begins at relative humidity a few tenths of a percent above saturation. Condensation of water onto condensation nuclei (or deposition of water vapor as ice on freezing nuclei) begins at a particular altitude known as the cloud base or lifting condensation level. Water molecules attach to the particles and form cloud droplets which have a radius of about 20 micrometers (0.02 mm) or less. The droplet volume is generally a million times greater than the typical condensation nuclei. Clouds are composed of large numbers of cloud droplets, or ice crystals, or both. Because of their small size and relatively high air resistance, they can remain suspended in the air for a long time, particularly if they remain in ascending air currents. The average cloud droplet has a terminal fall velocity of 1.3 cm per second in still air. To put this into perspective, the average cloud droplet falling from a typical low cloud base of 500 meters/1,650 feet would take more than 10 hours to reach the ground. We now know that cirrus clouds in their various forms are composed of ice crystals, and the upper levels of tall cumulus may also have ice in them even in the summer. While clouds in their varied forms and appearances (See Cloud Atlas) are a source of much interest, we will leave them now and continue up the Precipitation Ladder toward the top rung: Precipitation. Forming Precipitation Light Rain We know that not all clouds produce rain that strikes the ground. Some may produce rain or snow that evaporates before reaching the ground, and most clouds produce no precipitation at all. When rain falls, we know from measurements that the drops are larger than one millimeter. A raindrop of diameter 2 mm contains the water equivalent of a million cloud droplets (0.02 mm diameter). So if we are to get some precipitation from a cloud, there must be additional process within the cloud to form raindrops from cloud droplets. The next rung of the Precipitation Ladder is Buoyancy or Cloudiness which signifies that we must increase the cloud water content before we can expect any precipitation. This requires a continuation of the lifting process. It is assisted by 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 heat 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 rise. We can see the continued ascent of these parcels in cumulus clouds that reach great vertical growth. Now in the cloud, there must be Growth of cloud droplets to sizes that can fall to the ground as rain (we will look at snow in a minute) 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 become droplets. While the first condensation of water onto condensation nuclei to form cloud droplets occurs rather quickly, continued growth of cloud droplets in this manner will proceed very slowly. Second, growth by collision and coalescence of cloud droplets (and then the collision of rain 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 rapidly in size. As the drops grow, 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 m/s can quickly overtake a 0.05 mm (50 micrometer) drop falling at 0.27 m/s. When drops are too large, however, their collection efficiency for the smallest drops and droplets is not as great as when the drops are nearer in size. Small droplets may bounce off or flow around much larger drops and therefore do not coalesce. A drop about 60% smaller in diameter is most likely to be collected by a large drop. Clouds with strong updraft areas have the best drop growth because the drops and droplets stay in the cloud longer and thus have many more collision opportunities. Finally, it may seem odd, but the best conditions for drop growth occur when ice crystals are present in a cloud. When in small droplet form, liquid water must be cooled well below 0 ° C (32 °F) before freezing. In fact, under optimal conditions, a pure droplet may reach -40 °C before freezing. Therefore, there are areas within a cloud were ice crystals and water droplets co-exist. When ice crystals and supercooled droplets are near each other, there is a movement of water molecules from the droplet to the crystal. This increases the size of the ice crystal at the expense of the droplet. When the crystals grow at temperatures around -10 °C (14 °F), they begin to develop arms and branches, the stereotypical snow crystal. Such crystals not only are efficient at growing at the expense of water droplets, they also easily stick to one another forming large 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 have reached the top rung Precipitation. (For more on raindrops, click here.)The following table gives some typical drop diameters for various rain 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 precipitation falls as snow or some other solid water form. Actually, outside the tropical regions, it is likely that the much of the precipitation begins in the solid form and only becomes liquid rain when it melts while falling through air with temperatures above freezing. Most people call almost any frozen form of precipitation, other than hail or ice pellets, a snowflake. But meteorologists are a bit more fussy. Technically the term snowflake refers to an assemblage of individual snow crystals that have bumped together and remain joined during their fall. Snowflakes typically fall when air temperatures near the earth’s surface are not far from the freezing mark. Snow crystals adhere to each other better at these temperatures. At very cold temperatures, snowflakes are uncommon and we see mostly snow crystals during a snow fall. Snow crystals are typically 0.5 to 5 millimeters ( 0.02 to 0.20 inches) in size whereas snowflakes are about 10 mm in size (0.4 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 ice pellets, graupel or soft hail or snow grains, and a special form: freezing rain, also known as glaze or rime. The latter falls as a liquid but freezes on contact with an object. When clear ice forms, freezing rain is called glaze. When the ice is milky, it is called rime. Hail is a phenomenon of severe thunderstorms, requiring strong updrafts to form hailstones by passing the hailstone seed many times through air laden with drops and ice crystals. TOP What causes clouds? What influences the color of clouds? Why do clouds stop growing upwards? Why are there no clouds on some days? Types of clouds Low clouds Medium clouds High clouds Measuring clouds The formation of precipitation What causes clouds? A cloud is defined as ‘a visible aggregate of minute droplets of water or particles of ice or a mixture of both floating in the free 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 form in temperatures of -30 °C. If so, they are called supercooled droplets. Clouds at higher and extremely cold levels in the atmosphere are composed of ice crystals – these can be about a tenth of a millimeter long. Clouds form when the invisible water vapor in the air condenses into visible water droplets or ice crystals. For this to happen, the parcel of air must be saturated, i.e. unable to hold all the water it contains in vapor form, so it starts to condense into a liquid or solid form. There are two ways by which saturation is reached. (a) By increasing the water content in the air, e.g. through evaporation, to a point where the air can hold no more. (b) By cooling the air so that it reaches its dew point – this is the temperature at which condensation occurs, and is unable to ‘hold’ any more water. Figure 1 shows how there is a maximum amount of water vapor the air, at a given temperature, can hold. In general, the warmer the air, the more water vapor it can hold. Therefore, reducing its temperature decreases its ability to hold water vapor so that condensation occurs. Method (b) is the usual way that clouds are produced, and it is associated with air rising in the lower part of the atmosphere. As the air rises it expands due to lower atmospheric pressure, and the energy used in expansion causes the air to cool. Generally speaking, for each 100 meters/330 feet which the air rises, it will cool by 1 °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 slowly, at a rate of 0.5 ° C per 100 meters/330 feet. Therefore, the vertical ascent of air will reduce its ability to hold water vapor, so that condensation occurs. The height at which dew point is reached and clouds form is called the condensation level. There are five factors which can lead to air rising and cooling: 1. Surface heating, The ground is heated by the sun which heats the air in contact with it causing it to rise. The rising columns are often called thermals.2. Topography, Air forced to rise over a barrier of mountains or hills. This is known as orographic uplift.3. Frontal, A mass of warm air rising up 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 rise where they meet.5. Turbulence, A sudden change in wind speed with height creating turbulent eddies in the air. Another important factor to consider is that water vapor needs something to condense onto. Floating in the air are millions of minute salt, dust and smoke particles known as condensation nuclei which enable condensation to take place when the air is just saturated. What influences the color of clouds? Light from both the sky 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 part of the spectrum is scattered more strongly than other colors. The water droplets in the cloud are much larger, and these larger particles scatter all of the colors of the spectrum by about the same amount, so white light from the sun emerges from the clouds still white. Sometimes, clouds have a yellowish or brownish tinge – this is a sign of air pollution. Why do clouds stop growing upwards? Condensation involves the release of latent heat. This is the ‘invisible’ heat which a water droplet ‘stores’ when it changes from a liquid into a vapor. Its subsequent change of form again releases enough latent heat to make the damp parcel of air warmer than the air surrounding it. 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 main reason which stops clouds growing upwards is the end of the release of latent heat through the condensation process. There are two other factors which also play a role. 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 prevent further condensation. Why are there no clouds on some days? Even when it is very warm and sunny, there might not be any clouds and the sky is a clear blue. The usual reason for the absence of clouds will be the type of pressure, with the area being under the influence of a high pressure or anticyclone. Air would be sinking slowly, rather than rising and cooling. As the air sinks into the lower part of the atmosphere, the pressure rises, it becomes compressed and warms up, so that no condensation takes place. In simple terms, there are no mechanisms for clouds to form under these pressure conditions. Types of clouds In 1803 a retail chemist and amateur meteorologist called Luke Howard proposed a system which has subsequently become the basis of the present international classification. Howard also become known by some people as “the father of British meteorology”, and his pioneering work stemmed from his curiosity into the vivid sunsets in the late 18th century following 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 cloud 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-like, hairy or curled Nimbus – a rain bearer If we include another Latin word altum meaning height, the names of the ten main cloud types are all derived from these five words and based upon their appearance from ground level and visual characteristics. The cloud types are split into three groups according to the height of their base above mean sea level. Note that ‘medium’ level clouds are prefixed by the word alto and ‘high’ clouds by the word cirro (see Table 1). All heights given are approximate above sea 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 High clouds 17,000 – 35,000 ft LOW CLOUDS Cumulus (Cu) Height of base: 1,200-6,000 ft Color: White on its sunlit parts but with darker undersides. Shape: This cloud appears in the form of detached heaps. Shallow cumulus may appear quite ragged, especially in strong winds, but well formed clouds have flattened bases and sharp outlines. Large cumulus clouds have a distinctive “cauliflower” shape. Other features: Well developed cumulus may produce showers. Cumulonimbus (Cb) Height of base: 1,000-5,000 ft Color: White upper parts with dark, threatening undersides. Shape: A cumulus-type cloud of considerable vertical extent. When the top of a cumulus reaches great heights, the water droplets are transformed into ice crystals and it loses its clear, sharp outline. At this stage the cloud has become a cumulonimbus. Often, the fibrous cloud top 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: surface-1,500 ft Color: Usually grey. Shape: May appear as a layer with a fairly uniform base or in ragged patches, especially during precipitation falling from a cloud layer above. Fog will often lift into a layer of stratus due to an increase in wind or rise in temperature. As the sun heats the ground the base of stratus cloud may rise and break becoming shallow cumulus cloud as its edges take on a more distinctive form. Other features: If thin, the disc of the sun or moon will be visible (providing there are no other cloud layers above). If thick, it may produce drizzle or snow grains. Stratocumulus (Sc) Height of base: 1,200-7,000 ft Color: Grey or white, generally with shading. Shape: Either patches or a sheet of rounded elements but may also appear as an undulating layer. When viewed from the ground, the size of individual elements will have an apparent width of more than 5degree when at an elevation greater than 30degree (the width of 3 fingers at arm’s length). Other features: May produce light rain or snow. Sometimes the cloud may result from the spreading out of cumulus, giving a light shower. MEDIUM CL OUDS Altocumulus (Ac) Height of base: 7,000-17,000 ft Color: Grey or white, generally with some shading. Shape: Several different types, the most common being either patches or a sheet of rounded elements but may also appear as a layer without much form. When viewed from the ground, the size of individual elements will have an apparent width of 1 to 5degree when at an elevation greater than 30degree (the width of 1 to 3 fingers at arm’s length). Even if the elements appear smaller than this the cloud is still classified altocumulus if it shows shading. Other features: Occasionally some slight rain or snow, perhaps in the form of a shower may reach the ground. On rare occasions, a thunderstorm may occur from one type of Ac known as altocumulus castellanus — so called because in outline, the cloud tops look like a series of turrets and towers along a castle wall. Altostratus (As) Height of base: 8,000-17,000 ft Color: Greyish or bluish. Shape: A sheet of uniform appearance totally or partly covering the sky. Other features: Sometimes thin enough to reveal the sun or moon vaguely, as through ground glass. Objects on the ground do not cast shadows. May give generally light rain or snow, occasionally ice pellets, if the cloud base is no higher than about 10,000 ft. Nimbostratus (Ns) Height of base: 1,500-10,000 ft Color: Dark grey. Shape: A thick, diffuse layer covering all or most of the sky. Other features: Sun or moon always blotted out. Accompanied by moderate or heavy rain or snow, occasionally 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. HIGH CLOUDS Cirrus (Ci) Height of base: 17,000-35,000 ft Color: Composed of ice crystals, therefore white. Shape: Delicate hair-like filaments, sometimes hooked at the end; or in denser, entangled patches; or occasionally in parallel bands which appear to converge towards the horizon. Other features: The remains of the upper portion of a cumulonimbus is also classified as cirrus. Cirrocumulus (Cc) Height of base: 17,000-35,000 ft Color: Composed of ice crystals, therefore white. Shape: Patches or sheet of very small elements in the form of grains or ripples or a honeycomb. When viewed from the ground, the size of individual elements will have an apparent width of less than 1degree when at an elevation greater than 30degree (no greater than the width of a little finger at arm’s length). Other features: Sometimes its appearance in a regular pattern of ‘waves’ and small gaps may resemble the scales of a fish, thus giving rise to the popular name ‘mackerel sky’. (this name may also be attributed to high altocumulus clouds). Cirrostratus (Cs) Height of base: 17,000-35,000 ft Color: Composed of ice crystals, therefore white. Shape: A transparent veil of fibrous or smooth appearance totally or partly covering the sky. Other features: Thin enough to allow the sun to cast shadows on the ground unless it is low in the sky. Produces halo phenomena, the most frequent being the small (22degree ) halo around the sun or moon — a little more than the distance between the top of the thumb and the little finger spread wide apart at arm’s length. Condensation trails (contrails) These are thin trails of condensation, formed by the water vapor rushing out from the engines of jet aircraft flying at high altitudes. They are not true clouds, but can remain in the sky for a long time, and grow into cirrus clouds. Measuring clouds The cloud amount is defined as ‘the proportion of the celestial dome which is covered by cloud. The scale used is eighths, or oktas, with observers standing in an open space or on a rooftop to get a good view or panorama of the sky. Complete cloud cover is reported as 8 oktas, half cover as 4 oktas, and a completely clear sky as zero oktas. If there is low-lying mist or fog, the observer will report sky obscured. The reporter will also report the amount of each cloud level — 2 oktas of cumulus and 3 oktas of cirrus, etc. The frequent passage of depressions across the United Kingdom means that the most commonly reported cloud amount is, not surprisingly, 8 oktas. A clear blue sky, i.e. zero oktas, is less common, as often on hot, sunny days, there are small wispy layers of cirrostratus or fine tufts of thin cirrus at high altitudes. The formation of precipitation Cooling, condensation and cloud formation is the start of the process which results in precipitation. But not all clouds will produce raindrops or snowflakes — many are so short-lived and small that there are no opportunities for precipitation mechanisms to start. There are two theories that explain how minute cloud droplets develop into precipitation.1. The Bergeron-Findeisen ice-crystal mechanism If parcels of air are uplifted to a sufficient height in the troposphere, the dew point temperature will be very low, and minute ice crystals will start to form. The supercooled water droplets will also freeze on contact with these ice nuclei. The ice crystals subsequently combine to form larger flakes which attract more supercooled droplets. This process continues until the flakes fall back towards the ground. As they fall through the warmer layers of air, the ice particles melt to form raindrops. However, some ice pellets or snowflakes might be carried down to ground level by cold downdraughts.2. Longmuir’s collision and coalescence theory This applies to ‘warm’ clouds i.e. those without large numbers of ice crystals. Instead they contain water droplets of many differing sizes, which are swept upwards at different velocities so that they collide and combine with other droplets. It is thought that when the droplets have a radius of 3 mm, their movement causes them to splinter and disintegrate, forming a fresh supply of water droplets. Man-made rain In recent years, experiments have taken place, chiefly in the USA 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 aircraft of dry 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. TOP Clouds can form anywhere in the troposphere, and although condensed liquid, they are light enough to float 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: high, middle, low, and vertical development. Cloud names, of which there are twelve, combine appearance and height. A brief description of the root name will indicate this combination of features. Stratus, strato.Layered or sheetlike Cumulus, cumulo.Puffy, heaped (vertical) Nimbus, nimbo.Dark and rainy Cirrus, cirro.Curly, featherlike (high cloud) Alto.High (but used to describe a middle cloud) Fracto.Broken Let’s describe a few familiar cloud formations. The opposite of fog, in terms of altitude, are cirrus clouds. These clouds develop at an average height of 20,000 feet. Cirrus clouds look like a person’s hair, or feathers blowing in the wind. At this altitude, the air is so cold that the cloud is composed of ice crystals rather than water droplets found at lower altitudes.

1. The strong wind at this high altitude blow the clouds in long streamers across the sky.
2. Another cloud that is formed looks like sheets across the sky.
3. These are stratus clouds.
4. Stratus clouds form when condensation happens at the same level at which the air stops rising.
5. We 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 sky. One can make many shapes and designs by watching the clouds pass by overhead. These clouds have a flat bottom and a billowy 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 vapor condenses, forming the billowing columns.
• The remaining clouds have been named by combining terms.

For example, clouds that are sheet-like yet have vertical structure are called stratocumulus. The table below shows all 12 cloud names. While most rain clouds are in the low cloud range, because most moisture is nearer to the earth’s surface, special mention should be made of those clouds in the vertical development category. TOP

How clouds are formed step by step?

Water Vapor Evaporates Into the Air – The water and ice that make up clouds travels into the sky within air as water vapor, the gas form of water. Water vapor gets into air mainly by evaporation – some of the liquid water from the ocean, lakes, and rivers turns into water vapor and travels in the air.

What are four different ways how clouds are formed?

How are clouds formed and what factors affect their formation? Clouds form when air that is warm and moist cools and expands. Clouds are just tiny droplets of water in, As you can see from the image below, the air cools as it rises, but cool air is able to hold less water than warm air.

1. Thus, this excess water in the cool air condenses, and when enough of it does so, a cloud is formed.
2. [https://useruploads.socratic.org /vVgWLotETfO1GISQyp5N_how_clouds_form.jpg) : 1) surface heating, 2) mountains and terrains, 3) air masses that are forced to rise and cool, and 4) cold or warm weather fronts.1) The first process is perhaps the simplest: heats the earth and thus the air, this warm air rises, expands, and cools, forming clouds like in the image above.2) Clouds are also formed when air encounters mountains or other topography.

The air rises and cools and, again, the air cannot hold all of the water it held when warm so clouds form.3) The air is also forced to rise when wind in a low pressure system forces the air to rise up. Related to number 2, if air is forced to rise because of topography that slopes upwards, clouds may also form.4) Finally, cause cloud formation.

• Specifically, warm fronts create clouds because the warm air rises above the cold air and cold fronts create clouds because the cold air displaces or moves the warm air up.
• To conclude, many factors affect cloud formation, including topography, air temperature, and humidity.
• A very comprehensive link on cloud formation if you’re looking for more.

Additionally, clouds can form in areas where precipitation has been ongoing or particularly heavy. The falling precipitation brings moisture lower down in the atmosphere, and we get a ragged layer (either stratus or stratus fractus) form, usually within 1,500 ft of the ground or lower.

What keeps clouds in the sky?

This is an article from Curious Kids, a series for children of all ages. The Conversation is asking young people to send in questions they’d like an expert to answer. All questions are welcome. Skip to the bottom to see how to enter. How do the clouds stay up in the sky? – Samson, age four, London, UK.

Thanks for the question, Samson. Believe it or not, I once weighed a cloud and not many people can say they have done that! My scientist friends and I flew up into the sky in a giant airship, and went all the way through a fluffy, white cloud. Actually, it was very wet up there, because clouds are made up of billions of tiny water droplets.

As we flew through the cloud, we used lasers and other special scientific devices to measure how big the cloud was, and count how many tiny droplets of water were in it. Then, we did some maths and found that this cloud – which was actually pretty small, for a cloud – weighed four tonnes.

1. That’s the same as two elephants! So, you’re right to wonder how such a heavy thing can stay up in the sky.
2. There are three pieces to this puzzle, and the first one is gravity.
3. Like everything on this planet, the tiny droplets that make up a cloud are drawn towards the Earth by gravity.
4. But these droplets are so small that it’s hard for them to push past all the air beneath them.

This means that they don’t fall very fast at all – in fact, only about one centimetre per second, And any wind blowing upwards can carry the droplets back up. To fit the second piece of the puzzle, we’ll need to learn some proper chemistry; not too much, though, just enough for our story.

Let me introduce the periodic table: a map of all the elements that we humans know about. Elements are the building blocks of all things – just like the smallest pieces of Lego, which you use to build bigger and more complex objects. The periodic table is organised so that the lightest element of each row is always on the left.

Hydrogen is the lightest of all elements, so you’ll find it at the top left. As you move along each row from left to right, the elements get heavier and heavier. The periodic table of the elements (you might need to zoom in to see clearly).G.P. Moss/QMUL Click here for a larger, interactive version. Dry air is mostly made up of two gases, nitrogen and oxygen, plus a little bit of argon and tiny amounts of other gases.

For now, we can just focus on nitrogen and oxygen. As you can see on the periodic table, the weight of a single nitrogen atom is 14, while oxygen weighs almost 16. But neither nitrogen nor oxygen atoms like to be alone, so they almost always go in pairs – two atoms in a molecule, like two peas in a pod.

Because of this, a nitrogen molecule usually weighs 28, and an oxygen molecule weighs 32. As soon as we add water (H₂O) to the air, things get interesting. A water molecule is made up of two hydrogen atoms and one oxygen atom. Remember how hydrogen is the lightest element? Well, a single water molecule weighs just 18. Clouds often form at the top of mountains, where warm moist air blows upwards and then cools very quickly. Shutterstock. As warm, moist air rises, it gets cooler and cooler. And as it cools, more tiny water droplets form. You might expect the water droplets just to fall down as rain, but instead, something fun happens.

1. You know how sweat cools our skin when it dries and changes from liquid into gas? Well, when gas turns into liquid, the exact opposite happens: it actually gives off heat.
2. This means that the cloud droplets are now surrounded by a tiny blanket of warm air.
3. And what does warm air do? It rises! Not very far, though, because the air will cool again as it goes up.

Now our puzzle is complete: clouds are made up of tiny droplets of water, which are hardly affected by gravity, embedded in moist air, which is lighter than dry air. And they’re surrounded by tiny warm blankets of air, which lift them up towards the sky. CC BY-ND Please tell us your name, age and which town or city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question, but we will do our best. This article has been updated to reflect the effects of air resistance and gravity on cloud droplets more accurately.

Why are clouds white?

Why are clouds white? – Clouds are white because light from the Sun is white. As light passes through a cloud, it interacts with the water droplets, which are much bigger than the atmospheric particles that exist in the sky. When sunlight reaches an atmospheric particle in the sky, blue light is scattered away more strongly than other colours, giving the impression that the sky is blue.

Why do clouds grow?

How Clouds Form The presence of water-attracting nuclei alone is not enough for a cloud to form; the air temperature must also be below the dew point, the point of saturation where evaporation equals condensation. Air can reach the point of saturation in a number of ways.

The most common way is through air rising from the surface up into the atmosphere and cooling. As a block of air (a “parcel”) rises, it expands due to the lower pressure higher in the atmosphere. This expansion results in cooling. When the temperature changes due to expansion or contraction of the parcel rather than from heat transfer between the parcel and surrounding atmosphere, this is called the adiabatic process.

For each 1000-foot increase in elevation that the parcel rises, its air temperature will decrease by 5.5°F. (9.8°C per kilometer) until it reaches saturation. This is called the “dry lapse rate”. Once the parcel reaches saturation temperature (100% relative humidity), water vapor will condense onto the cloud condensation nuclei, resulting in the formation of a cloud droplet.

However, the atmosphere is in constant motion. As air rises, drier air is entrained, or mixed into the rising parcel, and both condensation and evaporation are continually occurring. As a result, cloud droplets are constantly forming and dissipating. When more water condenses on nuclei than evaporates from them, clouds form and grow.

Conversely, if there is more evaporation than condensation, clouds dissipate. This is why clouds appear and disappear as well as constantly change shape. Learning Lesson: : How Clouds Form

What is a cloud definition for kids?

Clouds What are clouds? A cloud is a large collection of very tiny droplets of water or ice crystals. The droplets are so small and light that they can float in the air. How are clouds formed? All air contains water, but near the ground it is usually in the form of an invisible gas called water vapor. When warm air rises, it expands and cools. Cool air can’t hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud. Why are clouds white? Since light travels as waves of different lengths, each color has its very own unique wavelength. Clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light. Why do clouds turn gray? Clouds are made up of tiny water droplets or ice crystals, usually a mixture of both. The water and ice scatter all light, making clouds appear white. If the clouds get thick enough or high enough all the light above does not make it through, hence the gray or dark look. Also, if there are lots of other clouds around, their shadow can add to the gray or multicolored gray appearance. Why do clouds float? A cloud is made up of liquid water droplets. A cloud forms when air is heated by the sun. As it rises, it slowly cools it reaches the saturation point and water condenses, forming a cloud. As long as the cloud and the air that its made of is warmer than the outside air around it, it floats! How do clouds move? Clouds move with the wind. Why do clouds form at different heights in the atmosphere? The characteristics of clouds are dictated by the elements available, including the amount of water vapor, the temperatures at that height, the wind, and the interplay of other air masses. How is fog formed? There are many different types of fog, but fog is mostly formed when southerly winds bring warm, moist air into a region, possibly ending a cold outbreak.

As the warm, moist air flows over much colder soil or snow, dense fog often forms. Warm, moist air is cooled from below as it flows over a colder surface. If the air is near saturation, moisture will condense out of the cooled air and form fog. With light winds, the fog near the ground can become thick and reduce visibilities to zero.

What are clouds? ☁☁ How are they formed? | Educational Vídeo for Kids

(Graphic Credit: USA TODAY.) Cloud Chart

Cloud Group	Cloud Height	Cloud Types
High Clouds = Cirrus	Above 18,000 feet	Cirrus Cirrostratus Cirrocumulus
Middle Clouds = Alto	6,500 feet to 18,000 feet	Altostratus Altocumulus
Low Clouds = Stratus	Up to 6,500 feet	Stratus Stratocumulus Nimbostratus

table>

Clouds with Vertical Growth Cumulus Cumulonimbus Special Clouds Mammatus Lenticular Fog Contrails

Cirrus Clouds Cirrus clouds are the most common of the high clouds. They are composed of ice and are thin, wispy clouds blown in high winds into long streamers. Cirrus clouds are usually white and predict fair to pleasant weather. By watching the movement of cirrus clouds you can tell from which direction weather is approaching. Cirrostratus clouds are thin, sheetlike high clouds that often cover the entire sky. They are so thin that the sun and moon can be seen through them. Cirrostratus clouds usually come 12-24 hours before a rain or snow storm. Cirrocumulus clouds appear as small, rounded white puffs that appear in long rows. The small ripples in the cirrocumulus clouds sometime resemble the scales of a fish. Cirrocumulus clouds are usually seen in the winter and indicate fair, but cold weather. In tropical regions, they may indicate an approaching hurricane. “Alto” Clouds Altostratus clouds are gray or blue-gray mid level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky. In the thinner areas of the clouds, the sun may be dimly visible as a round disk. Altostratus clouds often form ahead of storms with continuous rain or snow. Altocumulus clouds are mid level clouds that are made of water droplets and appear as gray puffy masses. They usually form in groups. If you see altocumulus clouds on a warm, sticky morning, be prepared to see thunderstorms late in the afternoon. Stratus Clouds Stratus clouds are uniform grayish clouds that often cover the entire sky. They resemble fog that doesn’t reach the ground. Light mist or drizzle sometimes falls out of these clouds. Stratocumulus clouds are low, puffy and gray. Most form in rows with blue sky visible in between them. Rain rarely occurs with stratocumulus clouds, however, they can turn into nimbostratus clouds. Nimbostratus clouds form a dark gray, wet looking cloudy layer associated with continuously falling rain or snow. They often produce precipitation that is usually light to moderate. Cumulus Clouds Cumulus clouds are white, puffy clouds that look like pieces of floating cotton. Cumulus clouds are often called “fair-weather clouds”. The base of each cloud is flat and the top of each cloud has rounded towers. When the top of the cumulus clouds resemble the head of a cauliflower, it is called cumulus congestus or towering cumulus. Cumulonimbus clouds are thunderstorm clouds. High winds can flatten the top of the cloud into an anvil-like shape. Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning and even tornadoes. The anvil usually points in the direction the storm is moving. Special Clouds Mammatus clouds are low hanging bulges that droop from cumulonimbus clouds. Mammatus clouds are usually associated with severe weather. Lenticular clouds are caused by a wave wind pattern created by the mountains. They look like discs or flying saucers that form near mountains. Fog is a cloud on the ground. It is composed of billions of tiny water droplets floating in the air. Fog exists if the atmospheric visibility near the Earth’s surface is reduced to 1 kilometer or less. Contrails are condensation trails left behind jet aircrafts. Contrails form when hot humid air from jet exhaust mixes with environmental air of low vapor pressure and low temperature. The mixing is a result of turbulence generated by the engine exhaust. Fractus clouds are small, ragged cloud fragments that are usually found under an ambient cloud base. They form or have broken off from a larger cloud, and are generally sheared by strong winds, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn pieces of cotton candy. Green Clouds are often associated with severe weather. The green color is not completely understood, but it is thought to have something to do with having a high amount of liquid water drops and hail inside the clouds. In the Great Plains region of the U.S. green clouds are associated with storms likely to produce hail and tornadoes. Cloud Activities Lesson Plan: Here is a great lesson plan on clouds. In this activity, kids see clouds form when they breath on spoons. When warm, moist breath hits the cool spoon, water vapor condenses and turns into a cloud-or water you can see. Note: This is a PDF file, so you need to have Adobe Acrobat Reader, Lesson Plan: Here is a great lesson plan on identifying clouds. In this activity, kids build a cloud finder and identify what clouds they see outside. Note: This is a PDF file, so you need to have Adobe Acrobat Reader, Lesson Plan: Here is a great lesson plan focusing on different types of clouds, how they are formed, and what they indicate about the weather. This activity is for grades 3-6. Note: This is a PDF file, so you need to have Adobe Acrobat Reader, Cloud Experiment: Here is a great experiment that allows the kids to make a cloud in a bottle. Fog Experiment: Here is a great experiment that allows the kids to make fog. Pressure Experiment: Here is an experiment that shows how pressure is created in our atmosphere by sucking an egg in a bottle. This is a very cool experiment! Make A Barometer Experiment: Here is an experiment that allows the kids to make a barometer. Evaporation Experiment: Here is an experiment that shows kids how evaporation takes place. Science Fair Project Ideas: Here is a complete list of science fair project ideas. Discover the science behind the weather that impacts us every day.

How do clouds stay together?

What holds clouds up, and why are some fluffy on top but flat on the bottom? Cumulus clouds often appear flat on the bottom revealing the lifted condensation level (LCL) the height in the atmosphere where rising air changes phase from water vapor to tiny liquid water droplets. (Photo credit: Steven A. Ackerman)

One of our readers awoke to some beautiful clouds in the summer sky recently, and those two excellent questions popped into her mind.Clouds are composed of tiny liquid water droplets (whose diameters are about the width of a human hair) and tiny shards of ice in a variety of shapes.Whether a cloud is mostly liquid water droplets or ice particles depends, as you might guess, on the temperature of the air in the cloud.Tiny cloud liquid water droplets can remain in the liquid state to temperatures as low as about -10 degrees Celsius (14 degrees Fahrenheit), and when they do they are known as supercooled liquid water droplets.

These droplets feel the downward force of gravity just like a baseball or a watermelon would. But because the droplets are so small, and therefore have small masses, the gravitational force can easily be balanced by an upward friction force resulting from the interaction of the droplets with the air molecules around them.

The droplets remain suspended, and that’s what holds clouds up in the air. When these droplets grow, they gain mass and eventually the gravitational force overwhelms the friction force and the now-larger droplets fall to the surface. The fluffy appearance of the tops of some clouds are evidence of convection, when buoyant air parcels within the cloud literally bubble to the top.

As the air rises, it encounters environments with lower and lower pressure and cools by expansion. This cooling increases the relative humidity of the air. Once that relative humidity gets to 100%, condensation of the invisible water vapor begins to produce liquid water droplets.

• The bottom of clouds often appears flat because the first level at which rising air parcels begin to condense is usually rather uniform over a given region.
• This level is known as the lifted condensation level — that is, the level at which lifted air parcels first begin to experience condensation.
• Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m.

the last Monday of each month. Send them your questions at or, : What holds clouds up, and why are some fluffy on top but flat on the bottom?

What is cloud made up of?

A cloud is made of water drops or ice crystals floating in the sky. There are many kinds of clouds. Clouds are an important part of Earth’s weather.

What three things are needed for cloud formation?

Learning Goals – This activity is designed for students to: 1. Create a cloud in a bottle.2. Observe, describe, discuss the cloud formation.3. Use the guided inquiry method to answer, “Why does the cloud form?” and “What does this have to do with weather?” The skills of critical thinking, synthesis of ideas, observation, questioning, and writing are developed.

What is cloud to snow called?

Thick, dense stratus or stratocumulus clouds producing steady rain or snow often are referred to as nimbostratus clouds.

Are clouds liquid or gas?

What is a cloud? – Many people believe that clouds are just made of water vapour (a gas). However, this is not strictly true. Water vapour is invisible, and it is around us all the time in the air. Sometimes there is more water vapour in the air and it feels humid or muggy.

Why are clouds important?

The Short Answer: Clouds play an important role in both warming and cooling our planet. Clouds give us a cooler climate on Earth than we would enjoy without clouds. However, as Earth’s climate warms, we won’t always be able to count on this cooling effect. A cloud-covered part of Earth, photographed by an Expedition 40 crew member on the International Space Station. Credit: NASA Clouds affect climate in two major ways. First, they are an essential part of the water cycle, Clouds provide an important link between the rain and snow, oceans and lakes, and plants and animals. Clouds are an important part of the water cycle here on Earth. Credit: NASA/JPL-Caltech Secondly, clouds also have an important effect on Earth’s temperature. But it’s a bit complicated: Clouds can both cool down and warm up the temperatures on Earth. Clouds can block light and heat from the Sun, making Earth’s temperature cooler. During the day, clouds can make the temperature on Earth cooler by blocking heat from the Sun. At night, clouds can make Earth’s temperature warmer by trapping heat that came from the Sun. Credit: NASA/JPL-Caltech So clouds can have both a cooling effect and a warming effect.

• When it comes to Earth’s climate, do clouds warm more than they cool, or is it the other way around? Well, that depends on where the clouds are in Earth’s atmosphere.
• Clouds within a mile or so of Earth’s surface tend to cool more than they warm.
• These low, thicker clouds mostly reflect the Sun’s heat.

This cools Earth’s surface. Clouds high up in the atmosphere have the opposite effect: They tend to warm Earth more than they cool. High, thin clouds trap some of the Sun’s heat. This warms Earth’s surface. Wispy clouds high up in the atmosphere generally make an area warmer. Lower-altitude clouds tend to help an area cool off. Credit: NASA/JPL-Caltech What about when you look at the effect of all clouds together? Cooling wins. Right now, Earth’s surface is cooler with clouds than it would be without the clouds. Clouds affect the climate and changes in the climate affect clouds. This relationship is called cloud-climate feedback. Credit: NASA/JPL-Caltech Climate scientists predict that as Earth’s climate warms, there will also be fewer clouds to cool it down. So, unfortunately, we can’t count on clouds alone to slow down the warming.

To understand clouds and their effect on climate, we also have to better understand the whole atmosphere. Scientists who try to predict changes in the climate are trying to understand the complex role of clouds in our atmosphere as they figure out how Earth is changing. Several NASA satellites are collecting information about clouds.

One, called CloudSat, is trying to figure out how much clouds contribute to changes in Earth’s climate. An artist’s illustration of NASA’s CloudSat spacecraft. CloudSat helps us understand how clouds affect Earth’s weather and climate. Credit: NASA/JPL

Can it rain without clouds?

Serein (/sɪˈriːn/; French: ) refers to rain falling from a cloudless sky. This sort of rain is said to take the form of a fine, light drizzle, typically after dusk.

Why do clouds go away at night?

METEOROLOGIST JEFF HABY Clouds are composed of liquid suspended water droplets in about a 100% RH environment. The three primary ways that clouds dissipate is by (1) the temperature increasing, (2) the cloud mixing with drier air, or (3) the air sinking within the cloud. When the temperature increases, the air has a higher capacity to evaporate liquid water. When a cloud’s temperature increases, evaporation occurs and reduces the liquid moisture content of the cloud. A cloud can be warmed by solar radiation and longwave emission from the earth’s surface. Daytime heating increases the capacity of the air to evaporate liquid water. Low clouds such as fog and low stratus are often dissipated due to daytime heating, especially if a cap exists aloft. Daytime heating’s power to erode clouds depends on the sun angle (depends on season), the cloud thickness and the overall stability and lift present in the troposphere. A cloud does not remain perfectly adiabatic (see tutorial below on adiabatic process), Some environmental air does mix into the cloud mass. If a cloud is no longer developing and not adding additional condensational moisture, the drier environmental air will gradually erode the cloud. Instead of having a sharp very defined appearance, after mixing with environmental air the cloud will look wispy with edges that are not well defined. This process is called entrainment. During entrainment, drier air incorporates itself into the cloud and induces evaporation. When air sinks, it warms adiabatically. Again, warming will induce evaporation and erosion of the cloud. This can occur when dynamic sinking mechanisms instigate or increase over a cloud or cloud field. Dynamic sinking mechanisms include low level CAA, NVA, low level divergence, and downslope flow. HOW DO CLOUDS DISSIPATE? Often, more than one of these processes mentioned above occurs simultaneously to erode a cloud or cloud deck.

Why do clouds turn black before rain?

Cloud Clouds are visible accumulations of tiny water droplets or ice crystals in the Earth’s atmosphere. Earth Science, Meteorology, Geography, Physical Geography Clouds are visible accumulations of tiny water droplets or ice crystals in the Earth’s atmosphere, Clouds differ greatly in size, shape, and color. They can appear thin and wispy, or bulky and lumpy. Clouds usually appear white because the tiny water droplets inside them are tightly packed, reflecting most of the sunlight that hits them.

White is how our eyes perceive all wavelengths of sunlight mixed together. When it’s about to rain, clouds darken because the water vapor is clumping together into raindrops, leaving larger spaces between drops of water. Less light is reflected. The rain cloud appears black or gray. Clouds form when air becomes saturated, or filled, with water vapor.

Warm air can hold more water vapor than cold air, so lowering the temperature of an air mass is like squeezing a sponge. Clouds are the visible result of that squeeze of cooler, moist air. Moist air becomes cloudy with only slight cooling. With further cooling, the water or ice particles that make up the cloud can grow into bigger particles that fall to Earth as precipitation,

Types of Clouds Because certain types of clouds are associated with certain types of weather, it is possible to forecast the weather by observing and understanding these different types of clouds.Clouds are classified into three main groups: cirrus, stratus, and cumulus,

Cirrus clouds are wispy, curly, or stringy. They are found high in the atmosphere—typically higher than 6,000 meters (20,000 feet)—and are usually made of ice crystals. Cirrus clouds usually signal clear, fair weather. Their shape often indicates the direction the wind is blowing high in the atmosphere.

Stratus clouds are horizontal and stratified, or layered. Stratus clouds can blanket the entire sky in a single pattern. They usually occur close to the Earth. Stratus clouds often form at the boundary of a warm front, where warm, moist air is forced up over cold air. This movement produces clouds as the moist air is cooled across the entire front.

The presence of stratus clouds usually means a chilly, overcast day. If precipitation falls from stratus clouds, it is usually in the form of drizzle or light snow, Cumulus clouds are large and lumpy. Their name comes from the Latin word meaning “heap” or “pile.” They can stretch vertically into the atmosphere up to 12,000 meters (39,000 feet) high.

Cumulus clouds are created by strong updrafts of warm, moist air. Most forms of heavy precipitation fall from cumulus clouds. The weather they bring depends on their height and size. The higher the base of a cloud is, the drier the atmosphere and the fairer the weather will be. Clouds located close to the ground mean heavy snow or rain.

Variations Clouds are also classified according to how high they are in the atmosphere and what kind of weather they produce.The prefix “cirro-” refers to clouds that lie more than 6,000 meters (20,000 feet) above the Earth. Cirrocumulus and cirrostratus clouds are two examples of these “high-level” clouds.The prefix “alto-” indicates clouds whose bases are between 2,000 and 6,000 meters (6,500-20,000 feet) above the Earth, such as altocumulus and altostratus clouds.

1. They are considered “mid-level” clouds and are mostly made of liquid water droplets, but can have some ice crystals in cold enough temperatures.
2. The prefix “nimbo-” or the suffix “-nimbus” are low-level clouds that have their bases below 2,000 meters (6,500 feet) above the Earth.
3. Clouds that produce rain and snow fall into this category.

(“Nimbus” comes from the Latin word for “rain.”) Two examples are the nimbostratus or cumulonimbus clouds. Nimbostratus clouds bring continuous precipitation that can last for many hours. These low-level clouds are full of moisture. Cumulonimbus clouds are also called thunderheads,

Thunderheads produce rain, thunder, and lightning, Many cumulonimbus clouds occur along cold fronts, where cool air is forced under warm air. They usually shrink as evening approaches, and moisture in the air evaporates, Cumulonimbus clouds gradually become stratocumulus clouds, which rarely produce rain.

Clouds and Weather Certain types of clouds produce precipitation. Clouds also produce the bolt of electricity called lightning and the sound of thunder that accompanies it. Lightning is formed in a cloud when positively charged particles and negatively charged particles are separated, forming an electrical field,

When the electrical field is strong enough, it discharges a superheated bolt of lightning to the Earth. Most of what we consider to be single lightning strikes are in fact three or four separate strokes of lightning. The sound of thunder is actually the sonic shock wave that comes when the air, heated by the lightning bolt, expands very rapidly.

Thunder sometimes sounds like it comes in waves because of the time it takes the sound to travel. Because the speed of light is faster than the speed of sound, lightning will always appear before its thunder is heard. Meteorologists measure cloud cover, or the amount of the visible sky covered by clouds, in units called oktas,

1. An okta estimates how many eighths of the sky (octo-) is covered in clouds.
2. A clear sky is 0 oktas, while a totally overcast or gray sky is 8 oktas.
3. Scientists have experimented with a process called cloud seeding for many years.
4. Cloud seeding aims to influence weather patterns.
5. Seeds, or microscopic particles, are placed in clouds.

These seeds are artificial cloud condensation nuclei (CCN), which are tiny particles of dust, salt, or pollution that collect in all clouds. Every raindrop and snowflake contains a CCN. Water or ice droplets accumulate around CCN. Scientists hope that cloud seeding will allow people to control precipitation.

1. Extraterrestrial Clouds Clouds exist in outer space.
2. Clouds on Jupiter, for instance, are divided into three bands in the planet ‘s atmosphere.
3. The highest band, at 50 kilometers above the surface of the planet, is mostly clear.
4. Jupiter’s middle layer of clouds is constantly moving.
5. These storm clouds appear as bands and swirls of yellow, brown, and red.

Most of these clouds are made of droplets of ammonia and ammonia crystals, mixed with phosphorus and sulfur, (These ammonia storms would be toxic on Earth.) Beneath Jupiter’s thick layer of ammonia clouds lies what some astrophysicists believe is a thin layer of water clouds.

Scientists think there may be water clouds because bursts of lightning have been spotted in Jupiter’s atmosphere. Interstellar clouds, which exist in the space between planets and stars, are not really clouds at all. Interstellar clouds are areas where gases and plasma are dense and, sometimes, visible.

Astronomers determine what elements are present in interstellar clouds by analyzing the light, or radiation, that comes from them. Most interstellar clouds are made of hydrogen, helium, and oxygen, The dusty “milk” of the Milky Way is an interstellar cloud between the stars of our galaxy,

Fast Fact Airavata Ancient Hindus believed the white elephant Airavata used his trunk to reach into the underworld and withdraw water. Airavata then sprayed this water into the sky, creating clouds and making precipitation possible. Fast Fact Contrails Contrails (short for condensation trails) are the linear clouds left behind a jet as it flies through the high atmosphere.

These manufactured clouds result when the hot air expelled from the jets engine cools and condenses in the surrounding air. Fast Fact Internet Cloud “Cloud” is sometimes used as a metaphor for the Internet. The “cloud condensation nuclei” in the Internet cloud are websites around which users gather and contribute.

Why do clouds turn grey before rain?

Why are some clouds grey and some white? › Friedrich-Alexander-Universität Erlangen-Nürnberg White clouds, grey clouds: Prof. Mölg explains why they come in different colours. (Image: Colourbox.de) Colours in the sky are the result of the scattering and refraction of sunlight as it travels to the earth’s surface.

Certain everyday phenomena in atmospheric optics – such as the sky’s blue colour – are familiar to us, while others are more spectacular and occur only under special conditions – such as a rainbow or a Fata Morgana. There are two factors that determine the colour of clouds. One is the size of the liquid and solid water particles in the cloud, which are known as hydrometeors.

The other is the number of these hydrometeors. If the cloud consists mainly of small droplets and ice crystals, sunlight can enter it relatively easily and is scattered diffusely. These kinds of clouds appear bright white. As the size and concentration of the hydrometeors increases, less and less sunlight penetrates the cloud, resulting in multiple scattering.

Why do clouds look red at night?

Why does a red sky appear at sunrise and sunset? – The saying is most reliable when weather systems predominantly come from the west as they do in the UK. “Red sky at night, shepherds delight” can often be proven true, since red sky at night means fair weather is generally headed towards you.

A red sky appears when dust and small particles are trapped in the atmosphere by high pressure. This scatters blue light leaving only red light to give the sky its notable appearance. A red sky at sunset means high pressure is moving in from the west, so therefore the next day will usually be dry and pleasant.

“Red sky in the morning, shepherds warning” means a red sky appears due to the high-pressure weather system having already moved east meaning the good weather has passed, most likely making way for a wet and windy low-pressure system.

What is cloud made up of?

A cloud is made of water drops or ice crystals floating in the sky. There are many kinds of clouds. Clouds are an important part of Earth’s weather.

How are clouds formed in biology?

When the temperature of a place becomes high, more water starts to evaporate. As a result, more water vapours are formed. Then, on reaching a certain height, water vapour present in the air condenses to form tiny droplets of water. These water droplets collect to form clouds that float in the air.

Is cloud solid liquid or gas?

Clouds form from water in the sky. The water may evaporate from the ground or move from other areas. Water vapor is always in the sky in some amount but is invisible. Clouds form when an area of air becomes cooler until the water vapor there condenses to liquid form.

Why do clouds stick together?

Hot WeekendAnd Why Do Clouds Stick Together? (Pt 3) It looks like the first week of June will be solidly in the “summery” column. A ridge of high pressure will give us a sunny Friday with valley highs in the upper 80s. The 80s will stay through the weekend, although Sunday will bring a slight cool down with breezy conditions. So why do clouds “stick together?” Perhaps the easiest way to answer is to talk about why those kinds of clouds form in the first place. First, the cloud doesn’t really “stick together”; because if you look carefully at time-lapse imagery you will see parts of the clouds evaporate, while other parts seem to form out of clear air. Cumulus form because small columns air rise and the water vapor condenses as the air cools. It is where this lifting occurs that the clouds seem to be sticking together, whereas in reality, it is a dynamic process of formation and dissipation. This happens with all cloud types. More on that tomorrow. : Hot WeekendAnd Why Do Clouds Stick Together? (Pt 3)