5. Winds

(1) When the air expands, it ________.

• (a) becomes solid
• ✔ (b) becomes thinner
• (c) gets lost
• (d) becomes humid

(2) From high air pressure regions, winds ________.

• (a) blow to regions of still higher pressure.
• (b) blow towards regions of cooler air.
• ✔ (c) blow towards regions of low air pressure.
• (d) remain still.

(3) In the northern hemisphere, winds blowing towards the equator ________ due to the rotation of the earth.

• (a) turn to the south
• (b) turn to the east
• ✔ (c) turn to the west
• (d) turn to the north

Note: Winds moving from the mid-latitudinal high pressure belt towards the equator deflect to their right in the northern hemisphere, making them blow from the north-east to the south-west (turning westwards).

(4) The direction of seasonal winds blowing over the Indian subcontinent during winter is from the ________.

• (a) south-east to north-west.
• (b) south-west towards north-east.
• ✔ (c) north-east to south-west.
• (d) north-west to south-east.

(5) The Roaring Forties in the southern hemisphere ________.

• (a) blow towards the equator.
• ✔ (b) blow in the areas around 40° S parallel.
• (c) blow from the subpolar region of low pressure.
• (d) blow around 40° N parallel.

(1) These winds from the south-west bring rains to the Indian subcontinent. During June to September, India gets rains. After this period these winds retreat.
Seasonal winds (South-west monsoon winds)

(2) These winds blowing from the north pole region towards 60° N parallel cause cold wave conditions in extensive areas covering North America, Europe and Russia.
Polar winds

(3) Hilltops get heated quickly during the day. The air in this part becomes hot, light and starts ascending. Hence, a low pressure area forms in this region. At the same time the air at the foothills being cooler, and that area experiences high pressure. Air in that area blows towards low pressure.
Valley breeze

(1) A belt of calm exists near the equator.
The region up to 5° north and 5° south of the equator receives perpendicular sunrays, causing intense heating. The heated air becomes lighter and moves vertically upwards towards the sky. As a result, horizontal winds do not blow in this region, making it a belt of calm (also called the Equatorial calm zone or Doldrums).

(2) The winds coming from the north-west in the southern hemisphere have greater velocities than the winds coming from the south-west in the northern hemisphere.
The southern hemisphere is mostly occupied by oceans, meaning the obstacle caused by the relief of the land surface (mountains, rough terrain) is almost absent. With no significant friction or obstacles, winds blow with much greater velocities in the southern hemisphere compared to the land-dominated northern hemisphere.

(3) The monsoon winds in the summer come from the sea but the retreating monsoon winds in winter come from land.
Monsoon winds are generated due to the uneven heating of land and water in different seasons. During summer, the land gets hotter than the sea, creating a low-pressure area over the land. Thus, winds blow from the high-pressure sea to the land. In winter, the land cools down faster, creating high pressure over the land while the sea remains relatively warmer with lower pressure. Hence, retreating monsoon winds blow from the land to the sea.

(1) Why is the air pressure high in polar areas in both the hemispheres?
In both polar regions, the temperature remains below 0°C throughout the year. Because of this freezing temperature, the air is cold, heavy, and dense. This heavy, descending air creates high-pressure belts in the polar areas (between 80° and 90° parallels) in both hemispheres.

(2) What effect does the rotation of the earth have on the winds?
The rotation of the earth from west to east causes a change in the original direction of the winds. In the northern hemisphere, winds get deflected towards the right of their original direction. In the southern hemisphere, winds get deflected towards the left of their original direction.

(3) Why do the cyclonic winds blow in a circular manner?
Cyclonic conditions are created when a low-pressure area is surrounded by high-pressure areas. Winds start blowing from the surrounding high pressure towards the central low pressure. Due to the earth's rotation, these winds get deflected, moving in an anticlockwise direction in the northern hemisphere and clockwise in the southern hemisphere, which makes them blow in a circular manner.

(4) State the reasons that lead to the formation of cyclones and describe the effects of cyclones.
Reasons for formation: Cyclones are formed when a low-pressure area develops and is completely surrounded by high-pressure areas, causing winds to rush towards the center.
Effects: During a cyclone, the sky remains cloudy, and winds blow with very high, unpredictable velocities accompanied by heavy rainfall. Since these storms are powerful, they often prove to be highly destructive, causing massive loss of property and life.