2 What is a cloud?Scientists define clouds as visible masses of droplets, frozen water floating in the Earth’s atmosphere that you can see from the ground. Another way to think of this is 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.
3 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.
4 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!
5 Types of Clouds Clouds are classified into three basic categories, depending largely on theheight of their bases above the ground.
6 High AltitudeClouds: Cirrus Cirrus means “curl of hair.”Cirrus clouds appear feathery or wispy.
7 Cirrus Clouds Cirrus clouds form in very cold air at high altitudes. Made of ice crystals, they have wispy or feathery appearance.Strong winds often blow streamers or “tails” off cirrus clouds.Theses features show the direction of the wind.You will usually see cirrus clouds in fair weather. However, they can be a sign that a storm is approaching.
8 Middle Altitude Clouds: Cumulus Cumulus means “heap” or “pile.”Cumulus-type clouds can grow to be very tall.
9 Cumulus CloudsCumulus clouds are puffy white clouds with darker bases.They look like cotton balls floating in the sky.There are several varieties of cumulus clouds.Usually they appear in the daytime in fair weather, when warm air rises and its water vapor condenses.Cooler air sinks along the sides of the clouds, keeping cumulus clouds separate from one another.
10 Cumulonimbus CloudsThe tallest clouds are cumulonimbus clouds, or thunderheads.These clouds produce thunderstorms that drop heavy rainfall.A cumulonimbus cloud can tower 18 kilometers above Earth’s surface.By comparison, jet planes usually fly at about 10 kilometers.Strong high-altitude winds often cause the top of the cloud to jut out sharply.If cumulus clouds keep growing taller, they can produce showers.The precipitation usually lasts less than half an hour because there are spaces between the clouds.
11 Low Altitude Clouds: Stratus Stratus means “spread out.”Stratus-type clouds form in flat layers
12 Stratus cloudsStratus clouds form in layers when air cools over a large area without rising or when the air is gently lifted.Stratus clouds are smooth because they form without strong air movement.Stratus clouds that form at high altitudes are much thinner than low stratus clouds.The ice crystals in high stratus clouds can make it seem as if there’s a circle of colored light around the Sun or Moon.Have you ever noticed on some days that the whole sky looks gray? You were looking at stratus clouds.Some low stratus clouds are so dark that they completely block out the Sun. These clouds produce steady, light precipitation—unlike the brief showers that come from cumulus clouds.
13 Fog Fog is a cloud that rests on the ground. Like stratus clouds, fog has a smooth appearance.It usually forms when a surface is colder than the air above it.Water vapor in the air condenses as it cools, forming a thick mist.Fog on land tends to be heaviest at dawn, after the ground has cooled overnight.It clears as the ground is heated up by sunlight.For can look beautiful rolling over hills or partly covering structures such as bridges.However, it often makes transportation dangerous by limiting visibility.In the United States close to 700 people die each year in automobile accidents that occur in dense fog
14 Clouds with vertical development: Cumulus Clouds Cumulus clouds are puffy clouds that sometimes look like pieces of floating cotton. The base of each cloud is often flat and may be only 1000 m (330 ft) above the ground. The top of the cloud has rounded towers. When the top of the cumulus resembles the head of a cauliflower, it is called cumulus congestus or towering cumulus. These clouds grow upward, and they can develop into a giant cumulonimbus, which is a thunderstorm cloud.Cumulonimbus clouds are thunderstorm clouds that form if cumulus congestus clouds continue to grow vertically. Their dark bases may be no more than 300 m (1000 ft) above the Earth's surface. Their tops may extend upward to over 12,000 m (39,000 ft). Tremendous amounts of energy are released by the condensation of water vapor within a cumulonimbus. Lightning, thunder, and even violent tornadoes are associated with the cumulonimbus.