Wind

Wind: Wind is the movement of air (usually in a horizontal direction) in the atmosphere. It is caused by a difference in temperatures between different regions on the Earth.

This temperature difference occurs mainly because of the uneven heating of different parts of the Earth’s surface by the sun.

Thus, the air absorbs different amounts of heat, making it warm in places and cool in others. As air gets warmer, its particles spread out. In other words, air expands on heating. This makes the air lighter, or less dense, so it rises. As air cools, it becomes heavier, or more dense, and sinks.

As warm air rises, air from cooler areas flows in to take the place of the rising air. This sets up a current of air and we call it wind.

a) Uneven heating between the equator and the poles:

The region of Earth receiving the Sun’s direct rays is the equator. Here, air is heated and rises, leaving low pressure areas behind.

Moving to about thirty degrees north and south of the equator, the warm air from the equator begins to cool and sink. Between thirty degrees latitude and the equator, most of the cooling sinking air moves back to the equator.

The rest of the air flows toward the poles. The air movements toward the equator are called trade winds - warm, steady breezes that blow almost continuously.

b) Uneven heating of land and water:

During summer, the land warms up faster near the equator and most of the time the temperature of the land is higher than that of water in the oceans. This results in the heating of air. The heated air rises. This causes the winds to blow from the oceans towards the land. These winds are called monsoon winds.

The word monsoon is derived from the Arabic word ‘mausam’, which means ‘season’. Monsoons blow from the land toward the sea in winter and from the sea toward land in the summer.

India’s winters are cold and dry. The monsoon winds blow from the northeast and carry little moisture.. Most of India lies between the Tropic of Cancer and the equator, so the sun’s rays shine directly on the land.

The summer monsoon comes from the southwest; the winds carry moisture from the Indian Ocean and bring heavy rain from June to September.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Monsoon winds flow because of uneven heating of land and ___________
A. Water	B. Sky	C. Snow	D. Atmosphere
Right Option : A
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Question : 2

On Earth the wind from the North and the South blow towards the equator. From this, we can understand that :
A. Earth is round or spherical in shape		B. It is hotter in and around the equator
C. It is hotter in and around the north and the south pole		D. Wind doesn't flow from the east or the west.
Right Option : B
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