Clouds
Clouds are a visible collection of small water droplets and ice crystals suspended in the atmosphere. They play a crucial role in weather and climate by regulating temperature, storing and redistributing water, and producing rainfall.
How Clouds are Formed
Clouds form when moist air rises, cools, and condenses around tiny particles in the atmosphere. There are three main processes of cloud formation:
- Convection Lifting
- The Sun heats the Earth’s surface, increasing surface temperature.
- Evaporation occurs, and the water vapour rises.
- As it cools at higher altitudes, it condenses into clouds.
- Orographic Lifting
- Moist air is forced to rise over mountains.
- The rising air cools and condenses, forming clouds along the slopes and peaks.
- Frontal Uplifting (Convergence of Air Masses)
- Warm air masses meet cold air masses.
- Warm air is forced to rise above the cold air, where it cools and condenses into clouds.
Necessary Conditions for Cloud Formation:
- Availability of water vapour in the air.
- Presence of condensation nuclei (dust, smoke, or salt particles) that provide surfaces for condensation.
- A low enough temperature (dew point) for condensation to occur.
Measurement of Cloud Cover
- Weather satellites orbit the Earth and measure cloud cover in oktas (eighths) through remote sensing.
- Weather maps and TV forecasts use conventional symbols to represent cloudiness.
- Ground observations also estimate the sky covered by clouds in terms of oktas or percentages.
Classification of Clouds
Clouds are classified according to shape, height, and associated weather.
1. Types Based on Shape
- Stratus Clouds: Layered, flat, and feathery.
- Cumulus Clouds: Globular, heaped, and dome-shaped with dark bases.
- Cirrostratus Clouds: Thin sheets covering the sky, creating a milky appearance. They often form halos around the sun or moon.
2. Types Based on Associated Weather
- Nimbus Clouds: The prefix “nimbo” means rainfall.
- Cumulonimbus: Associated with heavy rainfall and thunderstorms.
- Nimbostratus: Associated with continuous rainfall.
3. Types Based on Height
- High Clouds (above 6,000 m):
- Cirrus: White, wispy, and fibrous with a feathery appearance.
- Cirrocumulus: Thin, patchy clouds made of ice crystals.
- Middle Clouds (2,000–6,000 m):
- Altocumulus: White or gray, bumpy, and arranged in lines or waves.
- Altostratus: Gray-blue sheets that partly or fully cover the sky.
- Low Clouds (below 2,000 m):
- Stratus: Lowest clouds, resembling fog; bring light showers and dull weather.
- Nimbostratus: Dark, dense, shapeless clouds that bring continuous rain.
- Cumulus: Detached, dome-shaped, and associated with convectional rainfall.
- Stratocumulus: Combination of stratus and cumulus; globular but bring little or no rain.
- Clouds of Great Vertical Extent:
- Cumulonimbus: Towering clouds with flat, dark bases and rounded or anvil-shaped tops; linked with thunderstorms.
Importance of Clouds
- Rainfall Supply: Essential for water resources on Earth.
- Energy Balance: Absorb and redistribute the Sun’s heat, regulating climate.
- Weather Indicator: Help determine atmospheric processes for the day.
- Sun Protection: Reduce the impact of direct solar radiation, lowering excessive evaporation and protecting skin.
Clouds and Rainfall
- Some clouds do not produce rainfall because droplets are too small and evaporate before reaching the ground.
- Other clouds contain large enough water droplets that fall as precipitation.