Clouds formation & Types of clouds – Geography UPSC Notes

Clouds formation & Types of clouds – Geography UPSC Notes

Clouds are an important part of the earth’s weather and climate. Clouds form when water condenses in the sky. Clouds are visible accumulations of tiny water droplets or ice crystals in the Earth’s atmosphere.

Clouds formation

• Clouds form when the invisible water vapor in the air condenses into visible water droplets or ice crystals.
• There is water around us all the time in the form of tiny gas particles, also known as water vapour.
• There are also tiny particles floating around in the air – such as salt and dust – these are called aerosols.
• The water vapour and the aerosols are constantly bumping into each other.
• When the air is cooled, some of the water vapour sticks to the aerosols when they collide – this is condensation.
• Eventually, bigger water droplets form around the aerosol particles, and these water droplets start sticking together with other droplets, forming clouds.
• Clouds form when the air is saturated and cannot hold any more water vapour, this can happen in two ways:
• The amount of water in the air has increased – for example through evaporation – to the point that the air cannot hold any more water.
• The air is cooled to its dew point – the point where condensation occurs – and the air is unable to hold any more water.
• The warmer the air is, the more water vapour it can hold.
• Clouds are usually produced through condensation – as the air rises, it will cool, and reducing the temperature of the air decreases its ability to hold water vapour so that condensation occurs.
• The height at which the dew point is reached and clouds form is called the condensation level.

How do Clouds form?

Clouds form from water in the sky. The water may evaporate from the ground or move from other areas. Water vapour may be invisible but it is always in the sky in some amount. Clouds form when an area of air becomes cooler until the water vapour there condenses to liquid form. The water will condense around dust, ice, or sea salt.

There are five factors that can lead to air rising and cooling and clouds forming.

1. Surface heating
2. Orographic barrier
3. Fronts
4. Convergence
5. Turbulence

1. Surface heating – This happens when 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. Surface heating tends to produce cumulus clouds.

2. Topography or orographic forcing – The topography – or shape and features of the area – can cause clouds to be formed. When air is forced to rise over a barrier of mountains or hills it cools as it rises. Layered clouds are often produced this way.

3. Frontal – Clouds are formed when a mass of warm air rises up over a mass of cold, dense air over large areas along fronts. A ‘front’ is the boundary between warm, moist air and cooler, drier air.

4. Convergence – Streams of air flowing from different directions are forced to rise where they flow together or converge. This can cause cumulus clouds and showery conditions.

5. Turbulence – A sudden change in wind speed with height creating turbulent eddies in the air.

The range of ways in which clouds can be formed and the variable nature of the atmosphere result in an enormous variety of shapes, sizes, and textures of clouds.

Types Of Clouds

There are four basic cloud categories observed in our atmosphere –

1. Cirrus
2. Cumulus
3. Stratus
4. Nimbus

The names for clouds are usually combinations of the following prefixes or suffixes:

• Stratus/strato = flat/layered and smooth
• Cumulus/cumulo = heaped up/puffy, like cauliflower
• Cirrus/cirro = High up/wispy
• Alto = Medium level
• Nimbus/Nimbo = Rain-bearing cloud

A combination of these four basic types can give rise to the following types of clouds:

High Altitude clouds:

• High-level clouds occur above about 20,000 feet and are given the prefix “cirro.”.
• Dueto cold tropospheric temperatures at these levels, the clouds primarily are composed
  of ice crystals, and often appear thin, streaky, and white (although a low sun angle,
  e.g., near sunset, can create an array of color on the clouds).
• Cirrus, Cirrostratus, and Cirrocumulus are the cloud types found here.

Middle Altitude Clouds:

• The bases of clouds in the middle level of the troposphere, given the prefix “alto,” appear between 6,500 and 20,000 feet.
• Depending on the altitude, time of year, and vertical temperature structure of the troposphere, these clouds may be composed of liquid water droplets, ice crystals, or a combination of the two, including supercooled droplets (i.e., liquid droplets whose temperatures are below freezing).
• The two main type of mid-level clouds are altostratus and altocumulus.

Low Altitude Clouds:

• Low-level clouds are not given a prefix, although their names are derived from “strato” or “cumulo,” depending on their characteristics. Low clouds occur below 6500 feet, and normally consist of liquid water droplets or even supercooled droplets, except during cold winter storms when ice crystals (and snow) comprise much of the clouds.
• The two main types of low clouds include stratus, which develop horizontally, and cumulus, which develop vertically.

Vertical Clouds:

• These are clouds that extend from the lower to the higher altitudes of the atmosphere.
• They form by thermal convection or frontal lifting, sustained by the powerful convectional current that holds and pushes the moisture in the clouds further upward.
• An example of a vertical cloud is the Cumulonimbus cloud.

Foggy Clouds:

• A layer of stratus clouds on or near the ground. These form close to the ground.
• Sometimes they make visibility very poor such that you can hardly see more than 60 away.

Shelf Clouds?

Shelf clouds - also known as Arcus clouds - are often associated with powerful storm systems, and many times they are reported as wall clouds, funnel clouds, or rotation.

• • These clouds are sometimes seen beneath cumulonimbus clouds, the dense, towering vertical cloud that causes intense rain.
  • They often appear ahead of powerful Thunderstorms with heavy rain, strong winds, and occasionally hail or tornadoes.

Formation:

When a cold downdraft from a cumulonimbus cloud reaches the ground, the cold air may spread rapidly along the ground, pushing existing warm moist air upwards. As the cold air descends, it pushes warm air upward, causing condensation and cloud formation. This process creates the distinct horizontal shape and appearance of a shelf cloud.

Do You Know?

Halo (optical phenomenon) – In the form of rings, arcs, pillars, or bright spots, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere (cirriform clouds, diamond dust, etc.)

Cloud Seeding

Cloud seeding is an artificial way to induce moisture in the clouds so as to cause rainfall. It is done by spreading either dry ice or more commonly, silver iodide aerosols, into the upper part of clouds.

There are three cloud seeding methods-

• Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them.
• Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense.
• Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain.

Applications of Cloud Seeding

• Agriculture: It creates rain, providing relief to drought-stricken areas. E.g.: ‘Project Varshadhari’ in Karnataka in 2017.
• Power Generation: Cloud seeding experiments have been shown to augment the production of hydroelectricity during the last 40 years in Tasmania, Australia.
• Water Pollution Control: Cloud seeding can help to maintain the minimum summer flow of the rivers and dilute the impact of treated wastewater discharges from municipalities and industries.
• Fog Dispersal, Hail Suppression, and Cyclone Modification: “Project Sky Water” of U.S.A. in 1962 for weather modification through cloud seeding aimed at fog dispersal, hail suppression, and cyclone modification. During the winter the cloud seeding program is used to increase the mountain snowpack so that additional runoff is received during the spring melt season. The seeding of cumulus clouds is to provide increased annual rainfall directly on the land.
• Tackle Air Pollution: Cloud seeding can potentially be used to settle down toxic air pollutants through the rain. E.g.: recently, Central Pollution Control Board along with other researchers was mulling the use of cloud seeding to tackle Delhi’s air pollution.
• Tourism: Cloud seeding can transform typically dry areas much more hospitable to enhance tourism.

Challenges

• Potential Side-effects: The chemicals used in cloud seeding might be potentially harmful. It does have the potential to harm plants, animals, and people, or the environment as a whole.
• Abnormal Weather Patterns: It might ultimately change climatic patterns on the planet. Places that normally receive moisture might start experiencing drought due to the artificial process of adding chemicals to the atmosphere to simulate rain.
• Expensive: It involves processes such as delivering chemicals to the sky and releasing them into the air by flare shots or airplanes, which involves huge costs and logistic preparation.
• Pollution: As artificial rainfalls, seeding agents like silver iodide, dry ice, or salt will also fall. Residual silver discovered in places near cloud-seeding projects is considered toxic. As for dry ice, it can also be a source of greenhouse gas that contributes to global warming, as it is basically carbon dioxide.

Why are Clouds Important?

1. They are needed for rain or snow.
2. During the night, clouds reflect heat to the earth and keep the temperature warm.
3. During the day, clouds help in keeping the temperature cooler by shielding the sunlight.
4. Researching and studying clouds helps in understanding weather and climate.