Page 119 - SST Class 07

lower than the pressure over the land. So the air
solid, liquid or gaseous state. The humidity level
blows from the land towards the sea and is called varies from place to place and time to time
as land breeze . depending upon the temperature conditions. If
temperature is high, the rate of evaporation will
be high and humidity too will be high. Similarly,
Return
Return Flow Flow
low temperature will result in low humidity.
The air in the equatorial regions has more
cool
warm sea b cool moisture than in other areas of the world. It has
warm
sea breezereeze
more moisture in summer season in comparison
of winter season. The amount of moisture
Sea breeze
decreases at higher places. But we do not find
moisture in the cold air of the
Return Flow Flow polar region.
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When the air is full of water
vapour, it is called a humid
cool lan warm day . We can measure humidity
warm
land breezed breeze
cool
with an instrument called
Hygrometer
hygrometer .
Land breeze
Local Winds Precipitation
These winds blow only during a particular period Precipitation is the process by which condensed
of the day or year in a small area. Loo, chinook, water falls down to the earth’s surface. Rainfall,
foehn and harmattan are some local winds. snowfall, hail or sleet are together known as
precipitation. Rainfall is the most important form
Loo : This hot and dry wind blows over the of precipitation . When tiny water droplets join
Northern Plains of India in the summer months of
together, they grow in size until they are unable to
May and June.
float in the air. Then they fall as rainfall or
Chinook : This warm and dry wind blows along snowfall. Huge masses of water droplets are called
the eastern side of the Rocky mountains in North clouds . When they fall on the earth in a liquid
America. It melts the snow, so only it is called form, it is called rain .
chinook or the snow-eater.
Types of Rainfall
Foehn : This warm and dry wind blows across the Rainfall is broadly categorised into three
Alps in winter and helps in ripening grapes in
types—convectional rainfall, relief rainfall and
France.
cyclonic rainfall.
Harmattan : This cool and dry wind blows over Convectional Rainfall : Convectional rainfall is
North-West Africa and brings succour from heat.
quite common in equatorial and tropical areas. As
F ind Outind Out these regions are hot, the air coming into contact
with the earth’s hot
Sun heats the Warm air rises, Rain can
Find out that how wind plays an important role in surface heats up and land and air cools and condenses then occur
forming clouds
above
our lives. rises vertically
Humidity producing a vertical
air current. The air
Water vapour is an important part of the cools down at the
atmosphere. Its presence in the air determines the
higher altitude and
moisture content and is called humidity or rapid condensation Sea Land
moisture . Moisture is found in the atmosphere in
occurs. The clouds Convectional rainfall
The Atmosphere
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