Chapter 5 - Winds
Q.1. Rewrite the following statements after choosing the correct option.
(1) When the air expands, it ______.
(a) becomes solid
(b) becomes thinner
(c) gets lost
(d) becomes humid
Ans: Option (b) – becomes thinner
(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.
Ans: Option (c) – blow towards regions of low air pressure
(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
Ans: Option (b) – turn to the east
(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.
Ans: Option (c) – north-east to south-west
(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.
Ans: Option (b) – blow in the areas around 40° S parallel
Q.2. Identify the type of winds from the description given below.
(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.
Ans: 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.
Ans: 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.
Ans: Mountain breeze.
Q.3. Given below are the values of air pressure in millibars. Using the same, draw diagrams to show a cyclone and an anticyclone.
990, 994, 996, 1000
Ans:
1030, 1020, 1010, 1000
Ans:
Q.4. State one reason why.
(1) A belt of calm exists near the equator.
Ans: The region up to 5°north and 5° south of the equator remains calm for most of the year. Due to low pressure, winds blow in this region. Therefore, a belt of calm exists near the equator.
(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.
Ans:
(i) Winds in the southern hemisphere blow with great velocities.
(ii) The southern hemisphere is mostly occupied by oceans.
(iii) In this hemisphere, the obstacle caused by the relief of the land surface is almost absent.
(iv) As there is no obstacle, winds blow with great velocities in the southern hemisphere as compared to the northern hemisphere.
(3) The monsoon winds in the summer come from the sea but the retreating monsoon winds in winter come from land.
Ans:
(i) During summer, the land remains comparatively hot and the sea water remains comparatively cool.
(ii) As a result, during summer, the air pressure on the land remains low and that on the sea water remains high. Therefore, the monsoon winds in the summer come from the sea.
(iii) During winter, the land remains comparatively cool and the sea water comparatively hot.
(iv) As its effect during winter is that the air pressure on the land remains high and that on the sea water remains low, retreating monsoon winds in winter come from land.
Q.5. Complete the flowchart:
Ans:
Q.6. Answer in short:
(1) Why is the air pressure high in polar areas in both the hemispheres?
Ans: In both polar regions, the temperature is below 0°C throughout the year. Hence, here, the air is cold. Therefore, the air pressure is high in polar areas in both hemispheres.
(2) What effect does the rotation of the earth have on the winds?
Ans:
(i) When we consider the earth as a whole, we find the direction of the winds is influenced by the rotation of the earth.
(ii) In the Northern hemisphere, they get deflected towards their original direction, whereas in the southern hemisphere, they get deflected towards the left of the original direction.
(iii) The rotation from west to east causes this change in the original direction of the winds.
(3) Why do the cyclonic winds blow in a circular manner?
Ans:
(i) Cyclonic conditions are created when a low-pressure area is surrounded by high-pressure areas.
(ii) In these conditions, winds start blowing towards the low pressure area from surrounding high pressure areas.
(iii) Therefore, the cyclonic winds blow in a circular manner.
(4) State the reasons that lead to the formation of cyclones and describe the effects of cyclones.
Ans:
Reasons that lead to the formation of a cyclone:
(i) The air pressure in a particular area is low.
(ii) The air pressure in the surrounding area is high.
Effects of cyclones:
(i) During a cyclone, the sky is cloudy, winds blow with a very high velocity, and it rains heavily.
(ii) Cyclonic winds may prove destructive as they may cause loss of property and life near coastal regions.