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RAAM TUITION MATERIAL
ICSE 8 STD GEOGRAPHY MATERIAL
LESSON 4: ATMOSPHERIC PRESSURE AND WINDS
2 MARKS:
1) What is atmospheric pressure?
The weight of the atmosphere pushing down on a unit area on the earth’s surface is called atmospheric
pressure
2) Define equatorial low pressure belt
In the equatorial low pressure region, especially between 50N and 50S latitudes, the temperature is high
throughout the year. So, the atmospheric pressure in this area is very low. This low pressure zone is called
the equatorial low pressure
3) Define polar high pressure belts
The polar regions are extremely cold throughout the year. In these regions, the atmospheric pressure is
always high. These regions are called polar high pressure belts
4) What is called horse latitudes?
The hot air rising over the equatorial belt moves towards the poles. By the time the air streams reach the
latitudes around 30ON and 30OS, they become cool and heavy and begin to sink. This creates belts of high
pressure in these two regions. These two high pressure regions are known as horse latitudes or subtropical
high pressure belts
5) What is called wind?
The horizontal movement of air is called wind
6) What are the types of winds?
There are two types of winds. They are
∑ Permanent winds
∑ Local winds
7) Define permanent winds
The winds that blow from the permanent high pressure belts towards the permanent low pressure belts
maintain their directions of flow throughout the year. It is called permanent or prevailing or planetary
winds
8) What is called Coriolis effect?
The apparent deflection of winds due to the earth’s rotation is called Coriolis effect
9) What are the three types of permanent winds?
There are three types of permanent winds. They are
∑ Trade winds
∑ Westerlies
∑ Polar winds
10) Define trade winds
The trade winds blow from the subtropical high pressure belts to the equatorial low pressure belt
11) Define westerlies
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The winds blowing from the subtropical high pressure belts to the subpolar low pressure belts are known
as the westerlies
12) Define antitrade winds
Antitrade winds is blow in directions opposite to those of the trade winds.
13) Define roaring forties
The latitudes 40OS and 60Os they blow with such force that sailors called these latitudes called roaring
forties
14) Define Polar easterlies
The polar winds blow from the polar high pressure belts to the subpolar low pressure belts. They are also
known as the polar easterlies because they blow from a somewhat easterly direction
15) What is called local winds?
Winds that arise due to local or regional changes in temperature or pressure are known as local winds]
16) Define land breeze
The air over the sea is, thus warmer and lighter. The warm air above the sea rises. So, the pressure over
the sea is lower than the pressure over the land. Air from the land, therefore blows out towards the sea.
This is known as land breeze
17) Define monsoon
The monsoon is a seasonal wind. It blows in a fixed direction during a particular season but reverses its
direction when the season changes
18) What is called valley breeze?
A valley breeze is an anabatic wind. In mountainous regions, the slopes usually receive more direct
sunlight than the valleys, which are relatively sheltered. Thus, the slopes warm up quickly during the day.
The air above them warms up, too and rises. This cooler air from the valleys to move upslope
19) What is called mountain breeze?
A mountain breeze is a katabatic wind. At night, the slopes cool down by radiating heat. The air above
them also cools down and this cold, heavy air rolls downslope under gravity.
20) Define loo
The dry, hot and dusty wind blowing in the plains of northern India during the summer months is also an
example of a local wind. It is known as loo and it causes a rise in temperature
21) Define cyclones
Cyclonic winds are irregular winds of short duration. They are caused by pressure systems known as
cyclones and anticyclones
22) What is called hurricanes?
During summer, violent cyclonic storms often develop over the tropical oceans between the 5O and 30O
latitudes in the Northern and Southern hemispheres. These storms have very strong winds rotating round
a calm centre with very low pressure. These storms are called hurricanes
23) How do the seasons affect the positions of the permanent pressure belts?
The permanent pressure belts do not remain at the same positions throughout the year. They shift slightly
northward when the Northern hemisphere tilts towards the sun, and a little southward when the southern
hemisphere tilts towards the sun
24) How does the rotation of the earth affect the permanent winds?
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Due to the rotation of the earth, these winds appear to be deflected to the right of their paths in the
Northern hemisphere and to the left of their paths in the southern hemisphere
25) Give four examples of local winds blowing in different parts of the world
∑ Loo
∑ Mistral
∑ Bora
∑ Foehn
5 Marks:
1) Draw a diagram showing the pressure belts of the world. Describe the high pressure belts
Diagram Fig No:4.1 Pg.No:24
Polar high pressure belts:
The Polar regions are extremely cold throughout the year. In these regions, the atmospheric pressure is
always high. These regions are called polar high pressure belts
Subtropical high pressure belts:
The hot air rising over the equatorial belt moves towards the poles. By the time the air streams reach the
latitudes around 30ON and 30OS, they become cool and heavy and begin to sink. This creates belts of high
pressure in these two regions. These two high pressure regions are known as horse latitudes or subtropical
high pressure belts. They are also called the belts of calm because the weather conditions in these regions
are stable.
2) Briefly describe the trade winds and the westerlies. Draw a diagram showing all the permanent winds
Trade Winds:
The trade winds blow from the subtropical high pressure belts to the equatorial low pressure belt. Winds
are named after the direction from which they blow. In the Northern hemisphere, the trade winds blow
from the north-east and are known as the north-east trade winds. In the southern Hemisphere, they blow
from the south-east and are known as south-east trade winds. The trade winds blow with great regularity.
They are so called because in the days of sailing ships these winds greatly helped overseas traders sailing
westwards in the tropics to cross the oceans
Westerlies:
The winds blowing from the subtropical high pressure belts to the subpolar low pressure belts are known
as the westerlies, as they blow from a somewhat westerly direction in both the hemispheres. The
westerlies blow from the south-west in the Northern Hemisphere and from the north- West in the southern
Hemisphere. They are called antitrade winds is blow in directions opposite to those of the trade winds.
The Westerlies blow in the temperate zones of the world.
The Westerlies are not as regular as the trade winds. However, in the Southern hemisphere, where there
are few large land masses to obstruct them, the westerlies blow with great force over the vast stretches of
Ocean. Between the latitudes 40OS and 60Os they blow with such force that sailors called these latitudes
called roaring forties Diagram:Fig:4.2 Pg.No:25
3) What causes monsoon winds to blow over India in summer and winter? How do these winds bring rain
to India?
Monsoon:
The monsoon is a seasonal wind. It blows in a fixed direction during a particular season but reverses its
direction when the season changes
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RAAM TUITION 393, INDIAN BANK COMPLEX,ANNA NAGAR, MADURAI-20 CELL:8940001375
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Summer:
During Summer, the interior of the continent of Asia gets extremely heated, and a low pressure zone
develops in this region. Moist winds from the high pressure zones over the Indian Ocean blow towards
this zone and causes heavy rainfall in summer. We call them the south west monsoon because they first
enter the Indian subcontinent from the south-west
Winter:
In winter, the temperature falls sharply and a high pressure zone develops over the Interior of Asia. The
sea remains warmer than the land, so the pressure over it is much lower. As a result, cool dry winds from
the interior of the continent blow towards the sea. The winter monsoon is also called north east monsoon
because it blows from the north-east.
In India, it brings rain over the south-eastern coast after crossing the Bay of Bengal
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RAAM TUITION 393, INDIAN BANK COMPLEX,ANNA NAGAR, MADURAI-20 CELL:8940001375