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A cloud is a mass of water droplets or ice crystals suspended in the atmosphere. They are formed when water vapor in the air condenses into water droplets or ice crystals. This occurs when air is unable to hold all the water it contains in vapor form. They do not fall, but stay in the air, because there is warm air all round the heavier water droplets. They are light enough to float in the air and move from place to place by the wind. They can form anywhere in the troposphere and are an important part of Earth’s weather.
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How are Clouds Formed?
Clouds are formed due to the presence of water vapor, i.e. the gaseous form of ice or water, in the air. Water vapor gets into air mainly by evaporation. Some of the water from oceans, seas and lakes get evaporated due to the heat of the sun giving rise to water vapor which travels in air. As this air rises into the atmosphere, it gets cooler and becomes difficult for it to hold all the water vapor. This is because as the air becomes cooler, it’s pressure drops. The water vapor thus released condenses upon contact with particles like dust or pollen. It then turns into small water droplets or ice crystals and a cloud is formed.
Even though that’s the simplest way to explain how clouds are formed, there are different ways in which they form. Let’s have a look at these:
- Sunlight heats the air just above the ground. The air rises because it becomes warmer, lighter and less denser than the air around it. As it rises, the temperature and pressure drops, causing water vapor to condense and forms clouds. Cumulus, cumulonimbus, mammatus, and stratocumulus clouds are formed this way.
- When air blows in the sides of mountains, it is forced to rise up into the atmosphere. The air cools as it rises, condenses and eventually forms clouds. Lenticular and stratus clouds are formed this way.
- Winds meet at the center of the low pressure area and is forced upwards as they have nowhere to go. This air cools, condenses and forms clouds. Altocumulus, altostratus, cirrocumulus clouds are formed through this process.
- A weather ‘front’ is where warm air meets cold air. The warm air rises up and produces clouds like nimbostratus amongst others.
- A sudden change in wind speed can create circulations in the air which can bring the air at the surface high up into the sky resulting in the formation of clouds.
Types of Clouds
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Clouds are divided into three groups based on their height above sea level.
Low clouds: 7000 ft above sea level
Medium clouds: 7000 to 17000 ft above sea level
High clouds: 17000 to 35000 ft above sea level
The ‘medium’ level clouds are prefixed by the word alto and ‘high’ level clouds by the word cirro.
Cumulus
Cumulus clouds develop on clear, sunny days. They appear in the late morning, grow, and then disappear toward evening. These are formed when the sun heats the ground directly below. The top part of these clouds are rounded and puffy, and are white when sunlit, while their bottoms are flat and relatively dark.
Stratus
These clouds resemble fog and are seen on overcast days. They hang low in the sky as a flat, featureless, grey clouds.
Stratocumulus
They are somewhat like stratus clouds that occur in patches with the sky visible in between. They too are low, puffy, grayish or whitish but when viewed from underneath, stratocumulus have a dark, honeycomb appearance. They are formed on cloudy days when there’s weak convection in the atmosphere.
Altostratus
These cloud partially or totally cover the sky. They appear as gray or bluish-gray sheets of cloud.
Nimbostratus
They are thick clouds and cover the sky in a dark grey layer. They are formed during rainfall or snowfall. They can extend from the low and middle layers of the atmosphere.
Altocumulus
They are formed on warm and humid mornings and are found high up in the sky. They can signal thunderstorm or onset of cooler temperatures.
Cirrus
They are usually formed during fair weather. They are thin and white and are made of ice crystals rather than water droplets.
Cirrocumulus
These clouds are found in winter and are relatively short lived. They are small and white and are found at high altitudes.
Cirrostratus
These clouds indicate warmer weather. They occur when there is a large amount of moisture in the upper atmosphere. They are transparent and whitish cloud formed by the refraction of the light on the ice crystals in the clouds.
Cumulonimbus
These are clouds that predict the onset of severe weather like rainfall, hail or even tornadoes. They span the low, middle, and high layers of the atmosphere. Their tops are always flattened and their bottoms are hazy and dark.
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Color of Clouds
Clouds get it’s color from the scattering of sunlight. The large water droplets in the cloud scatter all of the colors of the spectrum by about the same amount causing the cloud to appear white in color.
At times clouds appear grey. This happens when light scattered in a cloud is sent back upwards, or out to the sides of the cloud, making the tops and sides of the cloud whiter than the base which receives less light. This is found in rain clouds where the cloud droplets are bigger, thus scattering more light.
At sunrise or sunset, clouds appear red or orange in color. During this time, the Sun is very low in the sky and light has to travel through more of the atmosphere. This causes the blue light to get scattered and deflected away allowing more red and yellow light to reach the Earth.
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