Page 89 - Journeys Through Society-7

Saturation point: Air can hold only a certain amount of become too heavy to remain suspended in the air and
water vapour at a given temperature. When the air fall to the surface. When warm moist air cools, it
reaches its full capacity of holding water vapour, it is condenses to form thick clouds which bring rainfall in
said to be saturated. As the temperature of the the form of large drops of water. When the drops are
saturated air falls, the water vapour in it condenses to small, it is called drizzle. Rainfall is measured by an
form droplets of water which float in the air. Millions instrument called the rain gauge.
of such droplets together form clouds, which are kept In regions where hot air expands to rise up to high
from falling by air currents. Clouds are grouped altitudes, it forms thick clouds that cause a sudden
according to their shape and height. Some examples torrential rainfall called convectional rainfall. When
of different types of clouds are stratus, cirrus and high mountains come in the way of moist winds and
cumulus. Altitude affects the shape of clouds. As air force them to rise up their slopes and shed rainfall, it is
rises, it cools and clouds are formed but when the air known as relief or orographic rainfall. When warm and
descends from a great height, it gets warmer and the cold air meet, the lighter warm air ascends over the
clouds disappear. heavier cold air, condensing above it and resulting in
Precipitation cyclonic rainfall.

Precipitation is any form of water, in solid or liquid Snow is made up of flakes of tiny ice crystals that form
state, that falls on the Earth's surface. Precipitation a snow cloud.
can take several forms. Hail is made up of rounded lumps of ice and occurs

Rainfall occurs when droplets present in the clouds only in cumulonimbus clouds.

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AI tools can make forecasts more accurate by interacting
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Hail

Revision Notes

• The blanket of air that surrounds the Earth is called the atmosphere.
• The different layers of the atmosphere are: the troposphere, stratosphere, mesosphere,
thermosphere and exosphere.
• Weather may change after short durations but climatic conditions remain the same for a long period
of time.
• The different types of winds are permanent winds, seasonal winds, local winds and cyclonic winds.

• The temperature at which the air gets saturated is called the saturation point.
• Precipitation is any form of water, in solid or liquid state, that falls on the Earth's surface.
• The different forms of precipitation are: rainfall, snow and hail.

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